fp_library/types/

try_lazy.rs

//! Memoized lazy evaluation for fallible computations.
//!
//! Computes a [`Result`] at most once and caches either the success value or error. All clones
//! share the same cache. Available in both single-threaded [`RcTryLazy`] and thread-safe
//! [`ArcTryLazy`] variants.
//!
//! # Implementation
//!
//! `TryLazy<'a, A, E, Config>` is a newtype over `Lazy<'a, Result<A, E>, Config>`. This
//! delegates shared behavior (caching, cloning, hashing, ordering) to the inner `Lazy` while
//! providing an error-aware combinator API (`map`, `map_err`, `and_then`, `or_else`).
//!
//! # `Foldable` and error discarding
//!
//! The [`Foldable`](crate::classes::Foldable) implementation for
//! [`TryLazyBrand<E, Config>`](crate::brands::TryLazyBrand) treats `TryLazy` as a container of
//! zero or one success values. If the computation produces an `Err`, the fold sees an empty
//! container and returns the initial accumulator unchanged. The error value is silently discarded.
//! Use [`evaluate`](TryLazy::evaluate) directly if you need to inspect or handle errors.
//!
//! # Choosing between `TryLazy`, `Lazy<Result<A, E>>`, and `Result<Lazy, E>`
//!
//! - **[`TryLazy<A, E>`](TryLazy)**: Use when the computation itself may fail, and you want
//!   memoization of the entire outcome (success or error). The result is computed at most once;
//!   subsequent accesses return the cached `Ok` or `Err`.
//! - **`Lazy<Result<A, E>>`**: Equivalent in caching behavior, but does not participate in the
//!   `TryLazy` combinator API (`map_err`, `and_then`, `or_else`). Prefer `TryLazy` for
//!   ergonomics when working with fallible computations.
//! - **`Result<Lazy<A>, E>`**: The error is known eagerly (before any lazy computation). Use
//!   this when failure is detected up front and only the success path involves deferred work.
//!
//! # `TryLazy::map` vs `Lazy::ref_map` naming
//!
//! [`Lazy::ref_map`](crate::types::Lazy::ref_map) is named `ref_map` because it receives a
//! `&A` reference (the memoized value is borrowed, not moved). [`TryLazy::map`](TryLazy::map)
//! follows the same convention internally (the closure receives `&A` from the cached result), but
//! uses the name `map` to mirror [`Result::map`] and the other fallible-type combinators
//! (`map_err`, `and_then`, `or_else`). The mapping closure must clone or derive a new `B` from
//! the reference.

#[fp_macros::document_module]
mod inner {
	use {
		crate::{
			Apply,
			brands::TryLazyBrand,
			classes::{
				Deferrable,
				LazyConfig,
				LiftFn,
				Monoid,
				RefFoldable,
				RefFoldableWithIndex,
				RefFunctor,
				Semigroup,
				SendDeferrable,
				SendRefFunctor,
				WithIndex,
			},
			impl_kind,
			kinds::*,
			types::{
				ArcLazyConfig,
				Lazy,
				RcLazyConfig,
				TrySendThunk,
				TryThunk,
				TryTrampoline,
			},
		},
		fp_macros::*,
		std::{
			fmt,
			hash::{
				Hash,
				Hasher,
			},
		},
	};

	/// A lazily-computed, memoized value that may fail.
	///
	/// The computation runs at most once. If it succeeds, the value is cached.
	/// If it fails, the error is cached. Subsequent accesses return the cached result.
	///
	/// ### When to Use
	///
	/// Use `TryLazy` for memoized fallible computation. The `Result` is cached on first
	/// evaluation, and subsequent accesses return the cached outcome without re-running
	/// the closure. For non-memoized fallible deferred computation, use
	/// [`TryThunk`](crate::types::TryThunk). For stack-safe fallible recursion, use
	/// [`TryTrampoline`](crate::types::TryTrampoline).
	///
	/// ### Cache Chain Behavior
	///
	/// Chaining [`map`](TryLazy::map) or [`map_err`](TryLazy::map_err) calls creates a
	/// linked list of `Rc`/`Arc`-referenced cells. Each mapped `TryLazy` holds a reference
	/// to its predecessor, keeping predecessor values alive in memory. This is the same
	/// behavior as [`Lazy::ref_map`](crate::types::Lazy::ref_map).
	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	///
	/// ### Higher-Kinded Type Representation
	///
	/// The higher-kinded representation of this type constructor is [`TryLazyBrand<E, Config>`](crate::brands::TryLazyBrand),
	/// which is parameterized by both the error type and the [`LazyConfig`], and is polymorphic over the success value type.
	pub struct TryLazy<'a, A, E, Config: LazyConfig = RcLazyConfig>(
		/// The internal lazy cell wrapping a `Result<A, E>`.
		pub(crate) Lazy<'a, Result<A, E>, Config>,
	)
	where
		A: 'a,
		E: 'a;

	// -- Clone --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The instance to clone.")]
	impl<'a, A, E, Config: LazyConfig> Clone for TryLazy<'a, A, E, Config>
	where
		A: 'a,
		E: 'a,
	{
		#[document_signature]
		#[document_returns(
			"A new `TryLazy` instance that shares the same underlying memoized result."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let memo = TryLazy::<_, _, RcLazyConfig>::new(|| Ok::<i32, ()>(42));
		/// let cloned = memo.clone();
		/// assert_eq!(cloned.evaluate(), Ok(&42));
		/// ```
		fn clone(&self) -> Self {
			Self(self.0.clone())
		}
	}

	// -- Generic evaluate --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The `TryLazy` instance.")]
	impl<'a, A, E, Config: LazyConfig> TryLazy<'a, A, E, Config>
	where
		A: 'a,
		E: 'a,
	{
		/// Gets the memoized result, computing on first access.
		///
		/// ### Panics
		///
		/// If the initializer closure panics, the underlying [`LazyCell`](std::cell::LazyCell)
		/// (for [`RcLazyConfig`]) or [`LazyLock`](std::sync::LazyLock) (for [`ArcLazyConfig`])
		/// is poisoned. Any subsequent call to `evaluate` on the same instance or any of its
		/// clones will panic again. For panic-safe memoization, wrap the closure body with
		/// [`std::panic::catch_unwind`] and store the result as an `Err` variant.
		#[document_signature]
		///
		#[document_returns("A result containing a reference to the value or error.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = TryLazy::<_, _, RcLazyConfig>::new(|| Ok::<i32, ()>(42));
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		#[inline]
		pub fn evaluate(&self) -> Result<&A, &E> {
			self.0.evaluate().as_ref()
		}
	}

	// -- RcLazyConfig methods --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	#[document_parameters("The try-lazy cell instance.")]
	impl<'a, A, E> TryLazy<'a, A, E, RcLazyConfig>
	where
		A: 'a,
		E: 'a,
	{
		/// Creates a new `TryLazy` that will run `f` on first access.
		#[document_signature]
		///
		#[document_parameters("The closure that produces the result.")]
		///
		#[document_returns("A new `TryLazy` instance.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = TryLazy::<_, _, RcLazyConfig>::new(|| Ok::<i32, ()>(42));
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		#[inline]
		pub fn new(f: impl FnOnce() -> Result<A, E> + 'a) -> Self {
			TryLazy(Lazy::<'a, Result<A, E>, RcLazyConfig>::new(f))
		}

		/// Creates a `TryLazy` containing an already-computed success value.
		#[document_signature]
		///
		#[document_parameters("The success value to wrap.")]
		///
		#[document_returns("A new `TryLazy` instance that evaluates to `Ok(&a)`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, ()>::ok(42);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		#[inline]
		pub fn ok(a: A) -> Self {
			Self::new(move || Ok(a))
		}

		/// Creates a `TryLazy` containing an already-computed error value.
		#[document_signature]
		///
		#[document_parameters("The error value to wrap.")]
		///
		#[document_returns("A new `TryLazy` instance that evaluates to `Err(&e)`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, String>::err("error".to_string());
		/// assert_eq!(memo.evaluate(), Err(&"error".to_string()));
		/// ```
		#[inline]
		pub fn err(e: E) -> Self {
			Self::new(move || Err(e))
		}

		/// Returns a clone of the memoized result, computing on first access.
		///
		/// This is a convenience wrapper around [`evaluate`](TryLazy::evaluate) for cases
		/// where an owned `Result` is needed rather than a `Result` of references.
		#[document_signature]
		///
		#[document_returns("An owned `Result` clone of the memoized value.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, String>::ok(42);
		/// let owned: Result<i32, String> = memo.evaluate_owned();
		/// assert_eq!(owned, Ok(42));
		/// ```
		#[inline]
		pub fn evaluate_owned(&self) -> Result<A, E>
		where
			A: Clone,
			E: Clone, {
			self.evaluate().cloned().map_err(|e| e.clone())
		}

		/// Transforms the success value by creating a new `TryLazy` cell.
		///
		/// The original cell is evaluated on first access of the new cell. The mapping
		/// function receives a reference to the cached success value.
		///
		/// ### Why `E: Clone`?
		///
		/// The inner cell holds `Result<A, E>`. Mapping the success side requires cloning
		/// the error out of the `&E` reference when the result is `Err`, because the new
		/// cell must own its own cached `Result<B, E>`.
		#[document_signature]
		///
		#[document_type_parameters("The type of the mapped success value.")]
		///
		#[document_parameters("The function to apply to the success value.")]
		///
		#[document_returns("A new `RcTryLazy` that applies `f` to the success value of this cell.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, String>::ok(10);
		/// let mapped = memo.map(|a| a * 2);
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		/// ```
		#[inline]
		pub fn map<B: 'a>(
			self,
			f: impl FnOnce(&A) -> B + 'a,
		) -> RcTryLazy<'a, B, E>
		where
			E: Clone + 'a, {
			RcTryLazy::new(move || match self.evaluate() {
				Ok(a) => Ok(f(a)),
				Err(e) => Err(e.clone()),
			})
		}

		/// Maps a function over the memoized success value by reference.
		///
		/// This is the inherent method form of [`RefFunctor::ref_map`](crate::classes::ref_functor::RefFunctor::ref_map)
		/// for `RcTryLazy`. Evaluates the lazy cell and, if `Ok`, applies `f` to the referenced
		/// success value. If `Err`, clones the error into the new cell.
		///
		/// This is functionally identical to [`map`](TryLazy::map) but exists so that
		/// the `RefFunctor` trait implementation can delegate to an inherent method,
		/// matching the pattern used by [`RcLazy::ref_map`](crate::types::lazy::Lazy::ref_map).
		///
		/// ### Why `E: Clone`?
		///
		/// The inner cell holds `Result<A, E>`. Mapping the success side requires cloning
		/// the error out of the `&E` reference when the result is `Err`, because the new
		/// cell must own its own cached `Result<B, E>`.
		#[document_signature]
		#[document_type_parameters("The type of the mapped success value.")]
		#[document_parameters("The function to apply to the success value.")]
		#[document_returns("A new `RcTryLazy` that applies `f` to the success value of this cell.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, String>::ok(10);
		/// let mapped = memo.ref_map(|x| *x * 2);
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		/// ```
		#[inline]
		pub fn ref_map<B: 'a>(
			&self,
			f: impl Fn(&A) -> B + 'a,
		) -> RcTryLazy<'a, B, E>
		where
			E: Clone + 'a, {
			let this = self.clone();
			RcTryLazy::new(move || match this.evaluate() {
				Ok(a) => Ok(f(a)),
				Err(e) => Err(e.clone()),
			})
		}

		/// Transforms the error value by creating a new `TryLazy` cell.
		///
		/// The original cell is evaluated on first access of the new cell. The mapping
		/// function receives a reference to the cached error value.
		///
		/// ### Why `A: Clone`?
		///
		/// The inner cell holds `Result<A, E>`. Mapping the error side requires cloning
		/// the success value out of the `&A` reference when the result is `Ok`, because the
		/// new cell must own its own cached `Result<A, E2>`.
		#[document_signature]
		///
		#[document_type_parameters("The type of the mapped error value.")]
		///
		#[document_parameters("The function to apply to the error value.")]
		///
		#[document_returns("A new `RcTryLazy` that applies `f` to the error value of this cell.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, String>::err("error".to_string());
		/// let mapped = memo.map_err(|e| format!("wrapped: {}", e));
		/// assert_eq!(mapped.evaluate(), Err(&"wrapped: error".to_string()));
		/// ```
		#[inline]
		pub fn map_err<E2: 'a>(
			self,
			f: impl FnOnce(&E) -> E2 + 'a,
		) -> RcTryLazy<'a, A, E2>
		where
			A: Clone + 'a, {
			RcTryLazy::new(move || match self.evaluate() {
				Ok(a) => Ok(a.clone()),
				Err(e) => Err(f(e)),
			})
		}

		/// Transforms both the success and error values by creating a new `TryLazy` cell.
		///
		/// The original cell is evaluated on first access of the new cell. The success
		/// mapping function `f` receives a reference to the cached success value, and the
		/// error mapping function `g` receives a reference to the cached error value.
		/// Unlike `map` (which requires `E: Clone`) or `map_err` (which requires `A: Clone`),
		/// `bimap` needs neither because each branch is fully transformed.
		#[document_signature]
		///
		#[document_type_parameters(
			"The type of the mapped success value.",
			"The type of the mapped error value."
		)]
		///
		#[document_parameters(
			"The function to apply to the success value.",
			"The function to apply to the error value."
		)]
		///
		#[document_returns(
			"A new `RcTryLazy` that applies `f` to the success value or `g` to the error value of this cell."
		)]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let ok_memo = RcTryLazy::<i32, String>::ok(10);
		/// let mapped = ok_memo.bimap(|a| a * 2, |e| e.len());
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		///
		/// let err_memo = RcTryLazy::<i32, String>::err("error".to_string());
		/// let mapped = err_memo.bimap(|a| a * 2, |e| e.len());
		/// assert_eq!(mapped.evaluate(), Err(&5));
		/// ```
		#[inline]
		pub fn bimap<B: 'a, F: 'a>(
			self,
			f: impl FnOnce(&A) -> B + 'a,
			g: impl FnOnce(&E) -> F + 'a,
		) -> RcTryLazy<'a, B, F> {
			RcTryLazy::new(move || match self.evaluate() {
				Ok(a) => Ok(f(a)),
				Err(e) => Err(g(e)),
			})
		}
	}

	// -- From conversions for RcTryLazy --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<TryThunk<'a, A, E>> for TryLazy<'a, A, E, RcLazyConfig> {
		#[document_signature]
		#[document_parameters("The fallible thunk to convert.")]
		#[document_returns(
			"A new `TryLazy` instance that will evaluate the thunk on first access."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let thunk = TryThunk::new(|| Ok::<i32, ()>(42));
		/// let memo: RcTryLazy<i32, ()> = TryLazy::from(thunk);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		fn from(eval: TryThunk<'a, A, E>) -> Self {
			Self::new(move || eval.evaluate())
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<TryTrampoline<A, E>> for TryLazy<'a, A, E, RcLazyConfig> {
		#[document_signature]
		#[document_parameters("The fallible trampoline to convert.")]
		#[document_returns(
			"A new `TryLazy` instance that will evaluate the trampoline on first access."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let task = TryTrampoline::<_, ()>::ok(42);
		/// let memo: RcTryLazy<i32, ()> = TryLazy::from(task);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		fn from(task: TryTrampoline<A, E>) -> Self {
			Self::new(move || task.evaluate())
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<Lazy<'a, A, RcLazyConfig>> for TryLazy<'a, A, E, RcLazyConfig>
	where
		A: Clone + 'a,
		E: 'a,
	{
		#[document_signature]
		#[document_parameters("The lazy value to convert.")]
		#[document_returns("A new `TryLazy` instance that wraps the lazy value.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let lazy = Lazy::<_, RcLazyConfig>::pure(42);
		/// let memo: TryLazy<_, (), _> = TryLazy::from(lazy);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		fn from(memo: Lazy<'a, A, RcLazyConfig>) -> Self {
			Self::new(move || Ok(memo.evaluate().clone()))
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A: 'a, E: 'a> From<Result<A, E>> for TryLazy<'a, A, E, RcLazyConfig> {
		#[document_signature]
		#[document_parameters("The result to convert.")]
		#[document_returns("A new `TryLazy` instance that produces the result.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let ok_memo: RcTryLazy<i32, String> = RcTryLazy::from(Ok(42));
		/// assert_eq!(ok_memo.evaluate(), Ok(&42));
		///
		/// let err_memo: RcTryLazy<i32, String> = RcTryLazy::from(Err("error".to_string()));
		/// assert_eq!(err_memo.evaluate(), Err(&"error".to_string()));
		/// ```
		fn from(result: Result<A, E>) -> Self {
			Self::new(move || result)
		}
	}

	// -- From conversions for ArcTryLazy --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<TryThunk<'a, A, E>> for TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Send + Sync + 'a,
		E: Send + Sync + 'a,
	{
		/// Converts a [`TryThunk`] into an [`ArcTryLazy`] by eagerly evaluating the thunk.
		///
		/// `TryThunk` is `!Send`, so the result must be computed immediately to cross
		/// into the thread-safe `ArcTryLazy` world.
		#[document_signature]
		#[document_parameters("The fallible thunk to convert.")]
		#[document_returns("A new `TryLazy` instance containing the eagerly evaluated result.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let thunk = TryThunk::new(|| Ok::<i32, ()>(42));
		/// let memo: ArcTryLazy<i32, ()> = ArcTryLazy::from(thunk);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		fn from(eval: TryThunk<'a, A, E>) -> Self {
			let result = eval.evaluate();
			Self::new(move || result)
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<TryTrampoline<A, E>> for TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Send + Sync + 'static,
		E: Send + Sync + 'static,
	{
		/// Converts a [`TryTrampoline`] into an [`ArcTryLazy`] by eagerly evaluating the trampoline.
		///
		/// `TryTrampoline` is `!Send`, so the result must be computed immediately to cross
		/// into the thread-safe `ArcTryLazy` world.
		#[document_signature]
		#[document_parameters("The fallible trampoline to convert.")]
		#[document_returns("A new `TryLazy` instance containing the eagerly evaluated result.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let task = TryTrampoline::<_, ()>::ok(42);
		/// let memo: ArcTryLazy<i32, ()> = ArcTryLazy::from(task);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		fn from(task: TryTrampoline<A, E>) -> Self {
			let result = task.evaluate();
			Self::new(move || result)
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<Lazy<'a, A, ArcLazyConfig>> for TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Clone + Send + Sync + 'a,
		E: Send + Sync + 'a,
	{
		#[document_signature]
		#[document_parameters("The thread-safe lazy value to convert.")]
		#[document_returns("A new `TryLazy` instance that wraps the lazy value.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let lazy = Lazy::<_, ArcLazyConfig>::pure(42);
		/// let memo: TryLazy<_, (), _> = TryLazy::from(lazy);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		fn from(memo: Lazy<'a, A, ArcLazyConfig>) -> Self {
			Self::new(move || Ok(memo.evaluate().clone()))
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<Result<A, E>> for TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Send + Sync + 'a,
		E: Send + Sync + 'a,
	{
		#[document_signature]
		#[document_parameters("The result to convert.")]
		#[document_returns("A new `TryLazy` instance that produces the result.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let ok_memo: ArcTryLazy<i32, String> = ArcTryLazy::from(Ok(42));
		/// assert_eq!(ok_memo.evaluate(), Ok(&42));
		///
		/// let err_memo: ArcTryLazy<i32, String> = ArcTryLazy::from(Err("error".to_string()));
		/// assert_eq!(err_memo.evaluate(), Err(&"error".to_string()));
		/// ```
		fn from(result: Result<A, E>) -> Self {
			Self::new(move || result)
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> From<TrySendThunk<'a, A, E>> for TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Send + Sync + 'a,
		E: Send + Sync + 'a,
	{
		/// Converts a [`TrySendThunk`] into an [`ArcTryLazy`] without eager evaluation.
		///
		/// Unlike conversions from `TryThunk` or `TryTrampoline`, this conversion does
		/// **not** evaluate the thunk eagerly. The inner `Send` closure is passed directly
		/// into `ArcTryLazy::new`, so evaluation is deferred until first access.
		#[document_signature]
		#[document_parameters("The fallible send thunk to convert.")]
		#[document_returns("A thread-safe `ArcTryLazy` that evaluates the thunk on first access.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let thunk: TrySendThunk<i32, ()> = TrySendThunk::ok(42);
		/// let lazy: ArcTryLazy<i32, ()> = ArcTryLazy::from(thunk);
		/// assert_eq!(lazy.evaluate(), Ok(&42));
		/// ```
		fn from(thunk: TrySendThunk<'a, A, E>) -> Self {
			thunk.into_arc_try_lazy()
		}
	}

	// -- Cross-config conversions --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A: Clone + Send + Sync + 'a, E: Clone + Send + Sync + 'a>
		From<TryLazy<'a, A, E, RcLazyConfig>> for TryLazy<'a, A, E, ArcLazyConfig>
	{
		/// Converts an [`RcTryLazy`] into an [`ArcTryLazy`] by eagerly evaluating and cloning the
		/// result.
		///
		/// `RcTryLazy` is `!Send`, so the result must be computed immediately and cloned
		/// into the thread-safe `ArcTryLazy` world.
		#[document_signature]
		#[document_parameters("The `RcTryLazy` instance to convert.")]
		#[document_returns(
			"A new `ArcTryLazy` instance containing a clone of the eagerly evaluated result."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let rc_lazy = RcTryLazy::<i32, String>::ok(42);
		/// let arc_lazy: ArcTryLazy<i32, String> = ArcTryLazy::from(rc_lazy);
		/// assert_eq!(arc_lazy.evaluate(), Ok(&42));
		///
		/// let rc_err = RcTryLazy::<i32, String>::err("oops".to_string());
		/// let arc_err: ArcTryLazy<i32, String> = ArcTryLazy::from(rc_err);
		/// assert_eq!(arc_err.evaluate(), Err(&"oops".to_string()));
		/// ```
		fn from(source: TryLazy<'a, A, E, RcLazyConfig>) -> Self {
			let result: Result<A, E> = source.evaluate().cloned().map_err(Clone::clone);
			Self::new(move || result)
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A: Clone + 'a, E: Clone + 'a> From<TryLazy<'a, A, E, ArcLazyConfig>>
		for TryLazy<'a, A, E, RcLazyConfig>
	{
		/// Converts an [`ArcTryLazy`] into an [`RcTryLazy`] by eagerly evaluating and cloning the
		/// result.
		///
		/// The result is computed immediately and cloned into a new single-threaded
		/// `RcTryLazy` instance.
		#[document_signature]
		#[document_parameters("The `ArcTryLazy` instance to convert.")]
		#[document_returns(
			"A new `RcTryLazy` instance containing a clone of the eagerly evaluated result."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let arc_lazy = ArcTryLazy::<i32, String>::ok(42);
		/// let rc_lazy: RcTryLazy<i32, String> = RcTryLazy::from(arc_lazy);
		/// assert_eq!(rc_lazy.evaluate(), Ok(&42));
		///
		/// let arc_err = ArcTryLazy::<i32, String>::err("oops".to_string());
		/// let rc_err: RcTryLazy<i32, String> = RcTryLazy::from(arc_err);
		/// assert_eq!(rc_err.evaluate(), Err(&"oops".to_string()));
		/// ```
		fn from(source: TryLazy<'a, A, E, ArcLazyConfig>) -> Self {
			let result: Result<A, E> = source.evaluate().cloned().map_err(Clone::clone);
			Self::new(move || result)
		}
	}

	// -- Rc catch_unwind --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error value."
	)]
	impl<'a, A: 'a, E: 'a> TryLazy<'a, A, E, RcLazyConfig> {
		/// Creates a `TryLazy` that catches unwinds (panics), converting the
		/// panic payload using a custom conversion function.
		///
		/// The closure `f` is executed when the lazy cell is first evaluated.
		/// If `f` panics, the panic payload is passed to `handler` to produce
		/// the error value. If `f` returns normally, the value is wrapped in `Ok`.
		#[document_signature]
		///
		#[document_parameters(
			"The closure that might panic.",
			"The function that converts a panic payload into the error type."
		)]
		///
		#[document_returns(
			"A new `TryLazy` instance where panics are converted to `Err(E)` via the handler."
		)]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::<i32, i32>::catch_unwind_with(
		/// 	|| {
		/// 		if true {
		/// 			panic!("oops")
		/// 		}
		/// 		42
		/// 	},
		/// 	|_payload| -1,
		/// );
		/// assert_eq!(memo.evaluate(), Err(&-1));
		/// ```
		pub fn catch_unwind_with(
			f: impl FnOnce() -> A + std::panic::UnwindSafe + 'a,
			handler: impl FnOnce(Box<dyn std::any::Any + Send>) -> E + 'a,
		) -> Self {
			Self::new(move || std::panic::catch_unwind(f).map_err(handler))
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value."
	)]
	impl<'a, A> TryLazy<'a, A, String, RcLazyConfig>
	where
		A: 'a,
	{
		/// Creates a `TryLazy` that catches unwinds (panics).
		///
		/// This is a convenience wrapper around [`catch_unwind_with`](TryLazy::catch_unwind_with)
		/// that uses the default panic payload to string conversion.
		#[document_signature]
		///
		#[document_parameters("The closure that might panic.")]
		///
		#[document_returns("A new `TryLazy` instance where panics are converted to `Err(String)`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = TryLazy::<_, String, RcLazyConfig>::catch_unwind(|| {
		/// 	if true {
		/// 		panic!("oops")
		/// 	}
		/// 	42
		/// });
		/// assert_eq!(memo.evaluate(), Err(&"oops".to_string()));
		/// ```
		pub fn catch_unwind(f: impl FnOnce() -> A + std::panic::UnwindSafe + 'a) -> Self {
			Self::catch_unwind_with(f, crate::utils::panic_payload_to_string)
		}
	}

	// -- Rc and_then / or_else --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	#[document_parameters("The `TryLazy` instance.")]
	impl<'a, A, E> TryLazy<'a, A, E, RcLazyConfig>
	where
		A: Clone + 'a,
		E: Clone + 'a,
	{
		/// Chains a fallible operation on the success value.
		///
		/// If this `TryLazy` succeeds, applies `f` to the cached `&A` and returns a new
		/// `TryLazy` that evaluates the result of `f`. If this `TryLazy` fails, the
		/// error is cloned into the new `TryLazy`.
		///
		/// Note: unlike the typical Rust `and_then` signature where the callback takes
		/// an owned `A`, this callback receives `&A` (a shared reference to the memoized
		/// value) because `TryLazy` caches its result behind a shared pointer.
		#[document_signature]
		///
		#[document_type_parameters("The type of the new success value.")]
		///
		#[document_parameters("The fallible function to apply to the success value.")]
		///
		#[document_returns("A new `TryLazy` containing the chained result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = RcTryLazy::new(|| Ok::<i32, String>(21));
		/// let chained = memo.and_then(|x| if *x > 0 { Ok(x * 2) } else { Err("negative".into()) });
		/// assert_eq!(chained.evaluate(), Ok(&42));
		/// ```
		pub fn and_then<B: 'a>(
			self,
			f: impl FnOnce(&A) -> Result<B, E> + 'a,
		) -> TryLazy<'a, B, E, RcLazyConfig> {
			let fa = self;
			TryLazy::<'a, B, E, RcLazyConfig>::new(move || match fa.evaluate() {
				Ok(a) => f(a),
				Err(e) => Err(e.clone()),
			})
		}

		/// Provides a fallback on the error value.
		///
		/// If this `TryLazy` fails, applies `f` to the cached `&E` and returns a new
		/// `TryLazy` that evaluates the result of `f`. If this `TryLazy` succeeds, the
		/// success value is cloned into the new `TryLazy`.
		#[document_signature]
		///
		#[document_parameters("The recovery function to apply to the error value.")]
		///
		#[document_returns("A new `TryLazy` containing the recovered result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Err("oops".into()));
		/// let recovered = memo.or_else(|_| Ok(42));
		/// assert_eq!(recovered.evaluate(), Ok(&42));
		/// ```
		pub fn or_else(
			self,
			f: impl FnOnce(&E) -> Result<A, E> + 'a,
		) -> TryLazy<'a, A, E, RcLazyConfig> {
			let fa = self;
			TryLazy::<'a, A, E, RcLazyConfig>::new(move || match fa.evaluate() {
				Ok(a) => Ok(a.clone()),
				Err(e) => f(e),
			})
		}
	}

	// -- ArcLazyConfig methods --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	#[document_parameters("The try-lazy cell instance.")]
	impl<'a, A, E> TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Send + Sync + 'a,
		E: Send + Sync + 'a,
	{
		/// Creates a new `TryLazy` that will run `f` on first access.
		#[document_signature]
		///
		#[document_parameters("The closure that produces the result.")]
		///
		#[document_returns("A new `TryLazy` instance.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = TryLazy::<_, _, ArcLazyConfig>::new(|| Ok::<i32, ()>(42));
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		#[inline]
		pub fn new(f: impl FnOnce() -> Result<A, E> + Send + 'a) -> Self {
			TryLazy(Lazy::<'a, Result<A, E>, ArcLazyConfig>::new(f))
		}

		/// Creates a thread-safe `TryLazy` containing an already-computed success value.
		#[document_signature]
		///
		#[document_parameters("The success value to wrap.")]
		///
		#[document_returns("A new `ArcTryLazy` instance that evaluates to `Ok(&a)`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, ()>::ok(42);
		/// assert_eq!(memo.evaluate(), Ok(&42));
		/// ```
		#[inline]
		pub fn ok(a: A) -> Self {
			Self::new(move || Ok(a))
		}

		/// Creates a thread-safe `TryLazy` containing an already-computed error value.
		#[document_signature]
		///
		#[document_parameters("The error value to wrap.")]
		///
		#[document_returns("A new `ArcTryLazy` instance that evaluates to `Err(&e)`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, String>::err("error".to_string());
		/// assert_eq!(memo.evaluate(), Err(&"error".to_string()));
		/// ```
		#[inline]
		pub fn err(e: E) -> Self {
			Self::new(move || Err(e))
		}

		/// Returns a clone of the memoized result, computing on first access.
		///
		/// This is a convenience wrapper around [`evaluate`](TryLazy::evaluate) for cases
		/// where an owned `Result` is needed rather than a `Result` of references.
		/// Requires `Send + Sync` since `ArcTryLazy` is thread-safe.
		#[document_signature]
		///
		#[document_returns("An owned `Result` clone of the memoized value.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, String>::ok(42);
		/// let owned: Result<i32, String> = memo.evaluate_owned();
		/// assert_eq!(owned, Ok(42));
		/// ```
		#[inline]
		pub fn evaluate_owned(&self) -> Result<A, E>
		where
			A: Clone,
			E: Clone, {
			self.evaluate().cloned().map_err(|e| e.clone())
		}

		/// Transforms the success value by creating a new thread-safe `TryLazy` cell.
		///
		/// The original cell is evaluated on first access of the new cell. The mapping
		/// function receives a reference to the cached success value. The error type must
		/// be `Clone` because the new cell owns its own cached result.
		#[document_signature]
		///
		#[document_type_parameters("The type of the mapped success value.")]
		///
		#[document_parameters("The function to apply to the success value.")]
		///
		#[document_returns(
			"A new `ArcTryLazy` that applies `f` to the success value of this cell."
		)]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, String>::ok(10);
		/// let mapped = memo.map(|a| a * 2);
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		/// ```
		#[inline]
		pub fn map<B: Send + Sync + 'a>(
			self,
			f: impl FnOnce(&A) -> B + Send + 'a,
		) -> ArcTryLazy<'a, B, E>
		where
			E: Clone, {
			ArcTryLazy::new(move || match self.evaluate() {
				Ok(a) => Ok(f(a)),
				Err(e) => Err(e.clone()),
			})
		}

		/// Maps a function over the memoized success value by reference.
		///
		/// This is the `ArcTryLazy` counterpart of [`RcTryLazy::ref_map`](TryLazy::ref_map).
		/// Evaluates the lazy cell and, if `Ok`, applies `f` to the referenced success value.
		/// If `Err`, clones the error into the new cell.
		///
		/// This is functionally identical to [`map`](TryLazy::map) but exists so that
		/// the `SendRefFunctor` trait implementation can delegate to an inherent method,
		/// matching the pattern used by [`ArcLazy::ref_map`](crate::types::lazy::Lazy::ref_map).
		///
		/// Note: A blanket `RefFunctor` trait impl is not provided for `TryLazyBrand<E, ArcLazyConfig>`
		/// because the `RefFunctor` trait does not require `Send` on the mapping function, but
		/// `ArcTryLazy::new` requires `Send`. This inherent method adds the necessary `Send` bounds
		/// explicitly.
		///
		/// ### Why `E: Clone`?
		///
		/// The inner cell holds `Result<A, E>`. Mapping the success side requires cloning
		/// the error out of the `&E` reference when the result is `Err`, because the new
		/// cell must own its own cached `Result<B, E>`.
		#[document_signature]
		#[document_type_parameters("The type of the mapped success value.")]
		#[document_parameters("The function to apply to the success value.")]
		#[document_returns(
			"A new `ArcTryLazy` that applies `f` to the success value of this cell."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, String>::ok(10);
		/// let mapped = memo.ref_map(|x| *x * 2);
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		/// ```
		#[inline]
		pub fn ref_map<B: Send + Sync + 'a>(
			&self,
			f: impl Fn(&A) -> B + Send + 'a,
		) -> ArcTryLazy<'a, B, E>
		where
			E: Clone, {
			let this = self.clone();
			ArcTryLazy::new(move || match this.evaluate() {
				Ok(a) => Ok(f(a)),
				Err(e) => Err(e.clone()),
			})
		}

		/// Transforms the error value by creating a new thread-safe `TryLazy` cell.
		///
		/// The original cell is evaluated on first access of the new cell. The mapping
		/// function receives a reference to the cached error value. The success type must
		/// be `Clone` because the new cell owns its own cached result.
		#[document_signature]
		///
		#[document_type_parameters("The type of the mapped error value.")]
		///
		#[document_parameters("The function to apply to the error value.")]
		///
		#[document_returns("A new `ArcTryLazy` that applies `f` to the error value of this cell.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, String>::err("error".to_string());
		/// let mapped = memo.map_err(|e| format!("wrapped: {}", e));
		/// assert_eq!(mapped.evaluate(), Err(&"wrapped: error".to_string()));
		/// ```
		#[inline]
		pub fn map_err<E2: Send + Sync + 'a>(
			self,
			f: impl FnOnce(&E) -> E2 + Send + 'a,
		) -> ArcTryLazy<'a, A, E2>
		where
			A: Clone, {
			ArcTryLazy::new(move || match self.evaluate() {
				Ok(a) => Ok(a.clone()),
				Err(e) => Err(f(e)),
			})
		}

		/// Transforms both the success and error values by creating a new thread-safe
		/// `TryLazy` cell.
		///
		/// The original cell is evaluated on first access of the new cell. The success
		/// mapping function `f` receives a reference to the cached success value, and the
		/// error mapping function `g` receives a reference to the cached error value.
		/// Unlike `map` (which requires `E: Clone`) or `map_err` (which requires `A: Clone`),
		/// `bimap` needs neither because each branch is fully transformed.
		#[document_signature]
		///
		#[document_type_parameters(
			"The type of the mapped success value.",
			"The type of the mapped error value."
		)]
		///
		#[document_parameters(
			"The function to apply to the success value.",
			"The function to apply to the error value."
		)]
		///
		#[document_returns(
			"A new `ArcTryLazy` that applies `f` to the success value or `g` to the error value of this cell."
		)]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let ok_memo = ArcTryLazy::<i32, String>::ok(10);
		/// let mapped = ok_memo.bimap(|a| a * 2, |e| e.len());
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		///
		/// let err_memo = ArcTryLazy::<i32, String>::err("error".to_string());
		/// let mapped = err_memo.bimap(|a| a * 2, |e| e.len());
		/// assert_eq!(mapped.evaluate(), Err(&5));
		/// ```
		#[inline]
		pub fn bimap<B: Send + Sync + 'a, F: Send + Sync + 'a>(
			self,
			f: impl FnOnce(&A) -> B + Send + 'a,
			g: impl FnOnce(&E) -> F + Send + 'a,
		) -> ArcTryLazy<'a, B, F> {
			ArcTryLazy::new(move || match self.evaluate() {
				Ok(a) => Ok(f(a)),
				Err(e) => Err(g(e)),
			})
		}
	}

	// -- Arc catch_unwind --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error value."
	)]
	impl<'a, A: Send + Sync + 'a, E: Send + Sync + 'a> TryLazy<'a, A, E, ArcLazyConfig> {
		/// Creates a thread-safe `TryLazy` that catches unwinds (panics),
		/// converting the panic payload using a custom conversion function.
		///
		/// The closure `f` is executed when the lazy cell is first evaluated.
		/// If `f` panics, the panic payload is passed to `handler` to produce
		/// the error value. If `f` returns normally, the value is wrapped in `Ok`.
		#[document_signature]
		///
		#[document_parameters(
			"The closure that might panic.",
			"The function that converts a panic payload into the error type."
		)]
		///
		#[document_returns(
			"A new `ArcTryLazy` instance where panics are converted to `Err(E)` via the handler."
		)]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::<i32, i32>::catch_unwind_with(
		/// 	|| {
		/// 		if true {
		/// 			panic!("oops")
		/// 		}
		/// 		42
		/// 	},
		/// 	|_payload| -1,
		/// );
		/// assert_eq!(memo.evaluate(), Err(&-1));
		/// ```
		pub fn catch_unwind_with(
			f: impl FnOnce() -> A + std::panic::UnwindSafe + Send + 'a,
			handler: impl FnOnce(Box<dyn std::any::Any + Send>) -> E + Send + 'a,
		) -> Self {
			Self::new(move || std::panic::catch_unwind(f).map_err(handler))
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value."
	)]
	impl<'a, A> TryLazy<'a, A, String, ArcLazyConfig>
	where
		A: Send + Sync + 'a,
	{
		/// Creates a thread-safe `TryLazy` that catches unwinds (panics).
		///
		/// The closure is executed when the lazy cell is first evaluated. If the
		/// closure panics, the panic payload is converted to a `String` error and
		/// cached. If the closure returns normally, the value is cached as `Ok`.
		///
		/// This is a convenience wrapper around [`catch_unwind_with`](TryLazy::catch_unwind_with)
		/// that uses the default panic payload to string conversion.
		#[document_signature]
		///
		#[document_parameters("The closure that might panic.")]
		///
		#[document_returns(
			"A new `ArcTryLazy` instance where panics are converted to `Err(String)`."
		)]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = TryLazy::<_, String, ArcLazyConfig>::catch_unwind(|| {
		/// 	if true {
		/// 		panic!("oops")
		/// 	}
		/// 	42
		/// });
		/// assert_eq!(memo.evaluate(), Err(&"oops".to_string()));
		/// ```
		pub fn catch_unwind(f: impl FnOnce() -> A + std::panic::UnwindSafe + Send + 'a) -> Self {
			Self::catch_unwind_with(f, crate::utils::panic_payload_to_string)
		}
	}

	// -- Arc and_then / or_else --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	#[document_parameters("The `TryLazy` instance.")]
	impl<'a, A, E> TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Clone + Send + Sync + 'a,
		E: Clone + Send + Sync + 'a,
	{
		/// Chains a fallible operation on the success value (thread-safe variant).
		///
		/// If this `ArcTryLazy` succeeds, applies `f` to the cached `&A` and returns a
		/// new `ArcTryLazy` that evaluates the result of `f`. If this `ArcTryLazy`
		/// fails, the error is cloned into the new `ArcTryLazy`.
		///
		/// Note: unlike the typical Rust `and_then` signature where the callback takes
		/// an owned `A`, this callback receives `&A` (a shared reference to the memoized
		/// value) because `ArcTryLazy` caches its result behind a shared pointer.
		#[document_signature]
		///
		#[document_type_parameters("The type of the new success value.")]
		///
		#[document_parameters("The fallible function to apply to the success value.")]
		///
		#[document_returns("A new `ArcTryLazy` containing the chained result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo = ArcTryLazy::new(|| Ok::<i32, String>(21));
		/// let chained = memo.and_then(|x| if *x > 0 { Ok(x * 2) } else { Err("negative".into()) });
		/// assert_eq!(chained.evaluate(), Ok(&42));
		/// ```
		pub fn and_then<B: Send + Sync + 'a>(
			self,
			f: impl FnOnce(&A) -> Result<B, E> + Send + 'a,
		) -> TryLazy<'a, B, E, ArcLazyConfig> {
			let fa = self;
			TryLazy::<'a, B, E, ArcLazyConfig>::new(move || match fa.evaluate() {
				Ok(a) => f(a),
				Err(e) => Err(e.clone()),
			})
		}

		/// Provides a fallback on the error value (thread-safe variant).
		///
		/// If this `ArcTryLazy` fails, applies `f` to the cached `&E` and returns a
		/// new `ArcTryLazy` that evaluates the result of `f`. If this `ArcTryLazy`
		/// succeeds, the success value is cloned into the new `ArcTryLazy`.
		#[document_signature]
		///
		#[document_parameters("The recovery function to apply to the error value.")]
		///
		#[document_returns("A new `ArcTryLazy` containing the recovered result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let memo: ArcTryLazy<i32, String> = ArcTryLazy::new(|| Err("oops".into()));
		/// let recovered = memo.or_else(|_| Ok(42));
		/// assert_eq!(recovered.evaluate(), Ok(&42));
		/// ```
		pub fn or_else(
			self,
			f: impl FnOnce(&E) -> Result<A, E> + Send + 'a,
		) -> TryLazy<'a, A, E, ArcLazyConfig> {
			let fa = self;
			TryLazy::<'a, A, E, ArcLazyConfig>::new(move || match fa.evaluate() {
				Ok(a) => Ok(a.clone()),
				Err(e) => f(e),
			})
		}
	}

	// -- Deferrable --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> Deferrable<'a> for TryLazy<'a, A, E, RcLazyConfig>
	where
		A: Clone + 'a,
		E: Clone + 'a,
	{
		/// Defers a computation that produces a `TryLazy` value.
		///
		/// This flattens the nested structure: instead of `TryLazy<TryLazy<A, E>, E>`, we get `TryLazy<A, E>`.
		/// The inner `TryLazy` is computed only when the outer `TryLazy` is evaluated.
		#[document_signature]
		///
		#[document_parameters("The thunk that produces the lazy value.")]
		///
		#[document_returns("A new `TryLazy` value.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	classes::*,
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let lazy = TryLazy::<_, (), RcLazyConfig>::defer(|| RcTryLazy::new(|| Ok(42)));
		/// assert_eq!(lazy.evaluate(), Ok(&42));
		/// ```
		fn defer(f: impl FnOnce() -> Self + 'a) -> Self
		where
			Self: Sized, {
			Self::new(move || match f().evaluate() {
				Ok(a) => Ok(a.clone()),
				Err(e) => Err(e.clone()),
			})
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A, E> SendDeferrable<'a> for TryLazy<'a, A, E, ArcLazyConfig>
	where
		A: Clone + Send + Sync + 'a,
		E: Clone + Send + Sync + 'a,
	{
		/// Defers a computation that produces a thread-safe `TryLazy` value using a thread-safe thunk.
		///
		/// This flattens the nested structure: instead of `ArcTryLazy<ArcTryLazy<A, E>, E>`, we get `ArcTryLazy<A, E>`.
		/// The inner `TryLazy` is computed only when the outer `TryLazy` is evaluated.
		#[document_signature]
		///
		#[document_parameters("The thunk that produces the lazy value.")]
		///
		#[document_returns("A new `ArcTryLazy` value.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	classes::*,
		/// 	types::*,
		/// };
		///
		/// let lazy: ArcTryLazy<i32, ()> = ArcTryLazy::send_defer(|| ArcTryLazy::new(|| Ok(42)));
		/// assert_eq!(lazy.evaluate(), Ok(&42));
		/// ```
		fn send_defer(f: impl FnOnce() -> Self + Send + 'a) -> Self
		where
			Self: Sized, {
			Self::new(move || match f().evaluate() {
				Ok(a) => Ok(a.clone()),
				Err(e) => Err(e.clone()),
			})
		}
	}

	// -- Type aliases --

	/// Single-threaded fallible memoization alias.
	pub type RcTryLazy<'a, A, E> = TryLazy<'a, A, E, RcLazyConfig>;

	/// Thread-safe fallible memoization alias.
	pub type ArcTryLazy<'a, A, E> = TryLazy<'a, A, E, ArcLazyConfig>;

	// -- HKT --

	impl_kind! {
		impl<E: 'static, Config: LazyConfig> for TryLazyBrand<E, Config> {
			#[document_default]
			type Of<'a, A: 'a>: 'a = TryLazy<'a, A, E, Config>;
		}
	}

	// -- Semigroup --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The success value type.",
		"The type of the error."
	)]
	impl<'a, A: Semigroup + Clone + 'a, E: Clone + 'a> Semigroup for TryLazy<'a, A, E, RcLazyConfig> {
		/// Combines two `RcTryLazy` values by combining their success values.
		///
		/// Evaluates `a` first. If `a` is `Err`, returns the error immediately without
		/// evaluating `b`. If both succeed, combines the values using `Semigroup::append`.
		#[document_signature]
		///
		#[document_parameters("The first `TryLazy`.", "The second `TryLazy`.")]
		///
		#[document_returns("A new `RcTryLazy` containing the combined result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	classes::*,
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let a: RcTryLazy<String, ()> = RcTryLazy::new(|| Ok("Hello".to_string()));
		/// let b: RcTryLazy<String, ()> = RcTryLazy::new(|| Ok(" World".to_string()));
		/// let c = append::<_>(a, b);
		/// assert_eq!(c.evaluate(), Ok(&"Hello World".to_string()));
		/// ```
		fn append(
			a: Self,
			b: Self,
		) -> Self {
			RcTryLazy::new(move || {
				let a_val = match a.evaluate() {
					Ok(v) => v.clone(),
					Err(e) => return Err(e.clone()),
				};
				let b_val = match b.evaluate() {
					Ok(v) => v.clone(),
					Err(e) => return Err(e.clone()),
				};
				Ok(Semigroup::append(a_val, b_val))
			})
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The success value type.",
		"The type of the error."
	)]
	impl<'a, A: Semigroup + Clone + Send + Sync + 'a, E: Clone + Send + Sync + 'a> Semigroup
		for TryLazy<'a, A, E, ArcLazyConfig>
	{
		/// Combines two `ArcTryLazy` values by combining their success values.
		///
		/// Evaluates `a` first. If `a` is `Err`, returns the error immediately without
		/// evaluating `b`. If both succeed, combines the values using `Semigroup::append`.
		#[document_signature]
		///
		#[document_parameters("The first `ArcTryLazy`.", "The second `ArcTryLazy`.")]
		///
		#[document_returns("A new `ArcTryLazy` containing the combined result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	classes::*,
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let a: ArcTryLazy<String, ()> = ArcTryLazy::new(|| Ok("Hello".to_string()));
		/// let b: ArcTryLazy<String, ()> = ArcTryLazy::new(|| Ok(" World".to_string()));
		/// let c = append::<_>(a, b);
		/// assert_eq!(c.evaluate(), Ok(&"Hello World".to_string()));
		/// ```
		fn append(
			a: Self,
			b: Self,
		) -> Self {
			ArcTryLazy::new(move || {
				let a_val = match a.evaluate() {
					Ok(v) => v.clone(),
					Err(e) => return Err(e.clone()),
				};
				let b_val = match b.evaluate() {
					Ok(v) => v.clone(),
					Err(e) => return Err(e.clone()),
				};
				Ok(Semigroup::append(a_val, b_val))
			})
		}
	}

	// -- Foldable --

	#[document_type_parameters("The error type.", "The memoization configuration.")]
	impl<E: 'static, Config: LazyConfig> RefFoldable for TryLazyBrand<E, Config> {
		/// Maps the success value to a monoid by reference.
		///
		/// Forces evaluation and, if the computation succeeded, maps the value by
		/// reference. If the computation failed, returns the monoid identity element.
		#[document_signature]
		#[document_type_parameters(
			"The lifetime of the computation.",
			"The brand of the cloneable function to use.",
			"The type of the elements.",
			"The monoid type."
		)]
		#[document_parameters("The mapping function.", "The TryLazy to fold.")]
		#[document_returns("The monoid value.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let memo: RcTryLazy<i32, ()> = RcTryLazy::new(|| Ok(10));
		/// let result = explicit::fold_map::<RcFnBrand, TryLazyBrand<(), RcLazyConfig>, _, _, _, _>(
		/// 	|a: &i32| a.to_string(),
		/// 	&memo,
		/// );
		/// assert_eq!(result, "10");
		/// ```
		fn ref_fold_map<'a, FnBrand, A: 'a + Clone, M>(
			func: impl Fn(&A) -> M + 'a,
			fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
		) -> M
		where
			FnBrand: LiftFn + 'a,
			M: Monoid + 'a, {
			match fa.evaluate() {
				Ok(a) => func(a),
				Err(_) => Monoid::empty(),
			}
		}

		/// Folds the `TryLazy` from the right by reference.
		#[document_signature]
		#[document_type_parameters(
			"The lifetime of the computation.",
			"The brand of the cloneable function to use.",
			"The type of the elements.",
			"The type of the accumulator."
		)]
		#[document_parameters(
			"The function to apply to each element reference and the accumulator.",
			"The initial value of the accumulator.",
			"The TryLazy to fold."
		)]
		#[document_returns("The final accumulator value.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let memo: RcTryLazy<i32, ()> = RcTryLazy::new(|| Ok(10));
		/// let result = explicit::fold_right::<RcFnBrand, TryLazyBrand<(), RcLazyConfig>, _, _, _, _>(
		/// 	|a: &i32, b| *a + b,
		/// 	5,
		/// 	&memo,
		/// );
		/// assert_eq!(result, 15);
		/// ```
		fn ref_fold_right<'a, FnBrand, A: 'a + Clone, B: 'a>(
			func: impl Fn(&A, B) -> B + 'a,
			initial: B,
			fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
		) -> B
		where
			FnBrand: LiftFn + 'a, {
			match fa.evaluate() {
				Ok(a) => func(a, initial),
				Err(_) => initial,
			}
		}

		/// Folds the `TryLazy` from the left by reference.
		#[document_signature]
		#[document_type_parameters(
			"The lifetime of the computation.",
			"The brand of the cloneable function to use.",
			"The type of the elements.",
			"The type of the accumulator."
		)]
		#[document_parameters(
			"The function to apply to the accumulator and each element reference.",
			"The initial value of the accumulator.",
			"The TryLazy to fold."
		)]
		#[document_returns("The final accumulator value.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let memo: RcTryLazy<i32, ()> = RcTryLazy::new(|| Ok(10));
		/// let result = explicit::fold_left::<RcFnBrand, TryLazyBrand<(), RcLazyConfig>, _, _, _, _>(
		/// 	|b, a: &i32| b + *a,
		/// 	5,
		/// 	&memo,
		/// );
		/// assert_eq!(result, 15);
		/// ```
		fn ref_fold_left<'a, FnBrand, A: 'a + Clone, B: 'a>(
			func: impl Fn(B, &A) -> B + 'a,
			initial: B,
			fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
		) -> B
		where
			FnBrand: LiftFn + 'a, {
			match fa.evaluate() {
				Ok(a) => func(initial, a),
				Err(_) => initial,
			}
		}
	}

	// -- WithIndex --

	#[document_type_parameters("The error type.", "The memoization configuration.")]
	impl<E: 'static, Config: LazyConfig> WithIndex for TryLazyBrand<E, Config> {
		type Index = ();
	}

	// -- RefFoldableWithIndex --

	#[document_type_parameters("The error type.", "The memoization configuration.")]
	impl<E: 'static, Config: LazyConfig> RefFoldableWithIndex for TryLazyBrand<E, Config> {
		/// Maps the success value to a monoid by reference with the unit index.
		#[document_signature]
		#[document_type_parameters(
			"The lifetime of the computation.",
			"The brand of the cloneable function to use.",
			"The type of the computed value.",
			"The monoid type."
		)]
		#[document_parameters(
			"The function to apply to the index and the value reference.",
			"The TryLazy to fold."
		)]
		#[document_returns("The monoid value.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	classes::ref_foldable_with_index::RefFoldableWithIndex,
		/// 	types::*,
		/// };
		///
		/// let lazy: RcTryLazy<i32, ()> = RcTryLazy::new(|| Ok(10));
		/// let result = <TryLazyBrand<(), RcLazyConfig> as RefFoldableWithIndex>::ref_fold_map_with_index::<
		/// 	RcFnBrand,
		/// 	_,
		/// 	_,
		/// >(|_, x: &i32| x.to_string(), &lazy);
		/// assert_eq!(result, "10");
		/// ```
		fn ref_fold_map_with_index<'a, FnBrand, A: 'a + Clone, R: Monoid + 'a>(
			f: impl Fn((), &A) -> R + 'a,
			fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
		) -> R
		where
			FnBrand: LiftFn + 'a, {
			match fa.evaluate() {
				Ok(a) => f((), a),
				Err(_) => Monoid::empty(),
			}
		}
	}

	// -- RefFunctor --

	#[document_type_parameters("The type of the error.")]
	impl<E: 'static + Clone> RefFunctor for TryLazyBrand<E, RcLazyConfig> {
		/// Maps a function over the success value of the memoized result, where the function takes a reference.
		///
		/// Evaluates the `TryLazy` and, if `Ok`, applies `f` to the referenced success value.
		/// If `Err`, clones the error into the new cell.
		#[document_signature]
		///
		#[document_type_parameters(
			"The lifetime of the values.",
			"The type of the success value.",
			"The type of the result."
		)]
		///
		#[document_parameters(
			"The function to apply to the success value.",
			"The memoized fallible value."
		)]
		///
		#[document_returns("A new memoized fallible value containing the mapped result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	classes::*,
		/// 	types::*,
		/// };
		///
		/// let memo = RcTryLazy::<i32, String>::ok(10);
		/// let mapped = TryLazyBrand::<String, RcLazyConfig>::ref_map(|x: &i32| *x * 2, &memo);
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		/// ```
		fn ref_map<'a, A: 'a, B: 'a>(
			f: impl Fn(&A) -> B + 'a,
			fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
		) -> Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, B>) {
			fa.ref_map(f)
		}
	}

	// -- SendRefFunctor --

	#[document_type_parameters("The type of the error.")]
	impl<E: 'static + Clone + Send + Sync> SendRefFunctor for TryLazyBrand<E, ArcLazyConfig> {
		/// Maps a thread-safe function over the success value of the memoized result, where the function takes a reference.
		///
		/// Evaluates the `TryLazy` and, if `Ok`, applies `f` to the referenced success value.
		/// If `Err`, clones the error into the new cell.
		#[document_signature]
		///
		#[document_type_parameters(
			"The lifetime of the values.",
			"The type of the success value.",
			"The type of the result."
		)]
		///
		#[document_parameters(
			"The function to apply to the success value.",
			"The memoized fallible value."
		)]
		///
		#[document_returns("A new memoized fallible value containing the mapped result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	brands::*,
		/// 	classes::*,
		/// 	types::*,
		/// };
		///
		/// let memo = ArcTryLazy::<i32, String>::ok(10);
		/// let mapped = TryLazyBrand::<String, ArcLazyConfig>::send_ref_map(|x: &i32| *x * 2, &memo);
		/// assert_eq!(mapped.evaluate(), Ok(&20));
		/// ```
		fn send_ref_map<'a, A: Send + Sync + 'a, B: Send + Sync + 'a>(
			f: impl Fn(&A) -> B + Send + 'a,
			fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
		) -> Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, B>) {
			fa.ref_map(f)
		}
	}

	// -- Monoid --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A: Monoid + Clone + 'a, E: Clone + 'a> Monoid for TryLazy<'a, A, E, RcLazyConfig> {
		/// Returns the identity `RcTryLazy`, which evaluates to `Ok(A::empty())`.
		#[document_signature]
		///
		#[document_returns("An `RcTryLazy` producing the identity value wrapped in `Ok`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let t: RcTryLazy<String, ()> = empty();
		/// assert_eq!(t.evaluate(), Ok(&String::new()));
		/// ```
		fn empty() -> Self {
			RcTryLazy::new(|| Ok(Monoid::empty()))
		}
	}

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	impl<'a, A: Monoid + Clone + Send + Sync + 'a, E: Clone + Send + Sync + 'a> Monoid
		for TryLazy<'a, A, E, ArcLazyConfig>
	{
		/// Returns the identity `ArcTryLazy`, which evaluates to `Ok(A::empty())`.
		#[document_signature]
		///
		#[document_returns("An `ArcTryLazy` producing the identity value wrapped in `Ok`.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::{
		/// 	functions::*,
		/// 	types::*,
		/// };
		///
		/// let t: ArcTryLazy<String, ()> = empty();
		/// assert_eq!(t.evaluate(), Ok(&String::new()));
		/// ```
		fn empty() -> Self {
			ArcTryLazy::new(|| Ok(Monoid::empty()))
		}
	}

	// -- Hash --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The try-lazy value to hash.")]
	impl<'a, A: Hash + 'a, E: Hash + 'a, Config: LazyConfig> Hash for TryLazy<'a, A, E, Config> {
		/// Forces evaluation and hashes the result.
		#[document_signature]
		#[document_type_parameters("The type of the hasher.")]
		///
		#[document_parameters("The hasher state.")]
		///
		#[document_examples]
		///
		/// ```
		/// use {
		/// 	fp_library::types::*,
		/// 	std::{
		/// 		collections::hash_map::DefaultHasher,
		/// 		hash::{
		/// 			Hash,
		/// 			Hasher,
		/// 		},
		/// 	},
		/// };
		///
		/// let lazy = RcTryLazy::<i32, ()>::new(|| Ok(42));
		/// let mut hasher = DefaultHasher::new();
		/// lazy.hash(&mut hasher);
		/// let h1 = hasher.finish();
		///
		/// let mut hasher = DefaultHasher::new();
		/// Ok::<i32, ()>(42).hash(&mut hasher);
		/// let h2 = hasher.finish();
		///
		/// assert_eq!(h1, h2);
		///
		/// let lazy = ArcTryLazy::<i32, ()>::new(|| Ok(42));
		/// let mut hasher = DefaultHasher::new();
		/// lazy.hash(&mut hasher);
		/// let h3 = hasher.finish();
		///
		/// assert_eq!(h1, h3);
		/// ```
		fn hash<H: Hasher>(
			&self,
			state: &mut H,
		) {
			self.0.evaluate().hash(state)
		}
	}

	// -- PartialEq --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The try-lazy value to compare.")]
	impl<'a, A: PartialEq + 'a, E: PartialEq + 'a, Config: LazyConfig> PartialEq
		for TryLazy<'a, A, E, Config>
	{
		/// Compares two `TryLazy` values for equality by forcing evaluation of both sides.
		///
		/// Note: This will trigger computation if either value has not yet been evaluated.
		#[document_signature]
		#[document_parameters("The other try-lazy value to compare with.")]
		#[document_returns("`true` if the evaluated results are equal.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let a = RcTryLazy::<i32, ()>::new(|| Ok(42));
		/// let b = RcTryLazy::<i32, ()>::new(|| Ok(42));
		/// assert!(a == b);
		/// ```
		fn eq(
			&self,
			other: &Self,
		) -> bool {
			self.0.evaluate() == other.0.evaluate()
		}
	}

	// -- Eq --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	impl<'a, A: Eq + 'a, E: Eq + 'a, Config: LazyConfig> Eq for TryLazy<'a, A, E, Config> {}

	// -- PartialOrd --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The try-lazy value to compare.")]
	impl<'a, A: PartialOrd + 'a, E: PartialOrd + 'a, Config: LazyConfig> PartialOrd
		for TryLazy<'a, A, E, Config>
	{
		/// Compares two `TryLazy` values for ordering by forcing evaluation of both sides.
		///
		/// Note: This will trigger computation if either value has not yet been evaluated.
		#[document_signature]
		#[document_parameters("The other try-lazy value to compare with.")]
		#[document_returns(
			"The ordering between the evaluated results, or `None` if not comparable."
		)]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let a = RcTryLazy::<i32, ()>::new(|| Ok(1));
		/// let b = RcTryLazy::<i32, ()>::new(|| Ok(2));
		/// assert!(a < b);
		/// ```
		fn partial_cmp(
			&self,
			other: &Self,
		) -> Option<std::cmp::Ordering> {
			self.0.evaluate().partial_cmp(other.0.evaluate())
		}
	}

	// -- Ord --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The try-lazy value to compare.")]
	impl<'a, A: Ord + 'a, E: Ord + 'a, Config: LazyConfig> Ord for TryLazy<'a, A, E, Config> {
		/// Compares two `TryLazy` values for ordering by forcing evaluation of both sides.
		///
		/// Note: This will trigger computation if either value has not yet been evaluated.
		#[document_signature]
		#[document_parameters("The other try-lazy value to compare with.")]
		#[document_returns("The ordering between the evaluated results.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let a = RcTryLazy::<i32, ()>::new(|| Ok(1));
		/// let b = RcTryLazy::<i32, ()>::new(|| Ok(2));
		/// assert_eq!(a.cmp(&b), std::cmp::Ordering::Less);
		/// ```
		fn cmp(
			&self,
			other: &Self,
		) -> std::cmp::Ordering {
			self.0.evaluate().cmp(other.0.evaluate())
		}
	}

	// -- Display --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The try-lazy value to display.")]
	impl<'a, A: fmt::Display + 'a, E: fmt::Display + 'a, Config: LazyConfig> fmt::Display
		for TryLazy<'a, A, E, Config>
	{
		/// Forces evaluation and displays `Ok(value)` or `Err(error)`.
		#[document_signature]
		///
		#[document_parameters("The formatter.")]
		///
		#[document_returns("The formatting result.")]
		///
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		///
		/// let ok_lazy = RcTryLazy::<i32, String>::ok(42);
		/// assert_eq!(format!("{}", ok_lazy), "Ok(42)");
		///
		/// let err_lazy = RcTryLazy::<i32, String>::err("oops".to_string());
		/// assert_eq!(format!("{}", err_lazy), "Err(oops)");
		///
		/// let ok_arc = ArcTryLazy::<i32, String>::ok(42);
		/// assert_eq!(format!("{}", ok_arc), "Ok(42)");
		///
		/// let err_arc = ArcTryLazy::<i32, String>::err("oops".to_string());
		/// assert_eq!(format!("{}", err_arc), "Err(oops)");
		/// ```
		fn fmt(
			&self,
			f: &mut fmt::Formatter<'_>,
		) -> fmt::Result {
			match self.evaluate() {
				Ok(a) => write!(f, "Ok({})", a),
				Err(e) => write!(f, "Err({})", e),
			}
		}
	}

	// -- Debug --

	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error.",
		"The memoization configuration."
	)]
	#[document_parameters("The try-lazy value to format.")]
	impl<'a, A, E, Config: LazyConfig> fmt::Debug for TryLazy<'a, A, E, Config>
	where
		A: 'a,
		E: 'a,
	{
		/// Formats the try-lazy value without evaluating it.
		#[document_signature]
		#[document_parameters("The formatter.")]
		#[document_returns("The formatting result.")]
		#[document_examples]
		///
		/// ```
		/// use fp_library::types::*;
		/// let memo = TryLazy::<_, _, RcLazyConfig>::new(|| Ok::<i32, ()>(42));
		/// assert_eq!(format!("{:?}", memo), "TryLazy(..)");
		/// ```
		fn fmt(
			&self,
			f: &mut fmt::Formatter<'_>,
		) -> fmt::Result {
			f.write_str("TryLazy(..)")
		}
	}

	// -- Fix combinators --

	/// Computes a fixed point for `RcTryLazy`.
	///
	/// Constructs a self-referential `RcTryLazy` where the initializer receives a clone
	/// of the resulting fallible lazy cell. This enables recursive definitions where the
	/// result depends on the lazy cell itself.
	///
	/// # Caveats
	///
	/// **Panic on reentrant evaluation:** Forcing the self-reference inside `f` before
	/// the outer cell has completed initialization causes a panic, because `LazyCell`
	/// detects the reentrant access.
	#[document_signature]
	///
	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	///
	#[document_parameters(
		"The function that receives a fallible lazy self-reference and produces the result."
	)]
	///
	#[document_returns("A new `RcTryLazy` instance.")]
	///
	#[document_examples]
	///
	/// ```
	/// use fp_library::types::{
	/// 	try_lazy::rc_try_lazy_fix,
	/// 	*,
	/// };
	///
	/// let lazy = rc_try_lazy_fix(|_self_ref: RcTryLazy<i32, ()>| Ok(42));
	/// assert_eq!(lazy.evaluate(), Ok(&42));
	/// ```
	pub fn rc_try_lazy_fix<'a, A: Clone + 'a, E: Clone + 'a>(
		f: impl FnOnce(RcTryLazy<'a, A, E>) -> Result<A, E> + 'a
	) -> RcTryLazy<'a, A, E> {
		use crate::types::lazy::rc_lazy_fix;

		TryLazy(rc_lazy_fix(move |inner| {
			let self_ref = TryLazy(inner);
			f(self_ref)
		}))
	}

	/// Computes a fixed point for `ArcTryLazy`.
	///
	/// Constructs a self-referential `ArcTryLazy` where the initializer receives a clone
	/// of the resulting fallible lazy cell. This enables recursive definitions where the
	/// result depends on the lazy cell itself.
	///
	/// # Caveats
	///
	/// **Deadlock on reentrant evaluation:** Forcing the self-reference inside `f` before
	/// the outer cell has completed initialization causes a deadlock, because `LazyLock`
	/// blocks on the lock that the current thread already holds.
	#[document_signature]
	///
	#[document_type_parameters(
		"The lifetime of the computation.",
		"The type of the computed value.",
		"The type of the error."
	)]
	///
	#[document_parameters(
		"The function that receives a fallible lazy self-reference and produces the result."
	)]
	///
	#[document_returns("A new `ArcTryLazy` instance.")]
	///
	#[document_examples]
	///
	/// ```
	/// use fp_library::types::{
	/// 	try_lazy::arc_try_lazy_fix,
	/// 	*,
	/// };
	///
	/// let lazy = arc_try_lazy_fix(|_self_ref: ArcTryLazy<i32, ()>| Ok(42));
	/// assert_eq!(lazy.evaluate(), Ok(&42));
	/// ```
	pub fn arc_try_lazy_fix<'a, A: Clone + Send + Sync + 'a, E: Clone + Send + Sync + 'a>(
		f: impl FnOnce(ArcTryLazy<'a, A, E>) -> Result<A, E> + Send + 'a
	) -> ArcTryLazy<'a, A, E> {
		use crate::types::lazy::arc_lazy_fix;

		TryLazy(arc_lazy_fix(move |inner| {
			let self_ref = TryLazy(inner);
			f(self_ref)
		}))
	}
}
pub use inner::*;

#[cfg(test)]
#[expect(
	clippy::unwrap_used,
	clippy::panic,
	reason = "Tests use panicking operations for brevity and clarity"
)]
mod tests {
	use {
		super::*,
		crate::{
			brands::{
				RcFnBrand,
				TryLazyBrand,
			},
			types::{
				ArcLazyConfig,
				RcLazy,
				RcLazyConfig,
				TrySendThunk,
				TryThunk,
				TryTrampoline,
			},
		},
		quickcheck_macros::quickcheck,
		std::{
			cell::RefCell,
			rc::Rc,
			sync::Arc,
		},
	};

	/// Tests that `TryLazy` caches successful results.
	///
	/// Verifies that the initializer is called only once for success.
	#[test]
	fn test_try_memo_caching_ok() {
		let counter = Rc::new(RefCell::new(0));
		let counter_clone = counter.clone();
		let memo: RcTryLazy<i32, ()> = RcTryLazy::new(move || {
			*counter_clone.borrow_mut() += 1;
			Ok(42)
		});

		assert_eq!(*counter.borrow(), 0);
		assert_eq!(memo.evaluate(), Ok(&42));
		assert_eq!(*counter.borrow(), 1);
		assert_eq!(memo.evaluate(), Ok(&42));
		assert_eq!(*counter.borrow(), 1);
	}

	/// Tests that `TryLazy` caches error results.
	///
	/// Verifies that the initializer is called only once for error.
	#[test]
	fn test_try_memo_caching_err() {
		let counter = Rc::new(RefCell::new(0));
		let counter_clone = counter.clone();
		let memo: RcTryLazy<i32, i32> = RcTryLazy::new(move || {
			*counter_clone.borrow_mut() += 1;
			Err(0)
		});

		assert_eq!(*counter.borrow(), 0);
		assert_eq!(memo.evaluate(), Err(&0));
		assert_eq!(*counter.borrow(), 1);
		assert_eq!(memo.evaluate(), Err(&0));
		assert_eq!(*counter.borrow(), 1);
	}

	/// Tests that `TryLazy` shares the cache across clones.
	///
	/// Verifies that clones see the same result.
	#[test]
	fn test_try_memo_sharing() {
		let counter = Rc::new(RefCell::new(0));
		let counter_clone = counter.clone();
		let memo: RcTryLazy<i32, ()> = RcTryLazy::new(move || {
			*counter_clone.borrow_mut() += 1;
			Ok(42)
		});
		let shared = memo.clone();

		assert_eq!(memo.evaluate(), Ok(&42));
		assert_eq!(*counter.borrow(), 1);
		assert_eq!(shared.evaluate(), Ok(&42));
		assert_eq!(*counter.borrow(), 1);
	}

	/// Tests `catch_unwind`.
	///
	/// Verifies that panics are caught and converted to errors.
	#[test]
	fn test_catch_unwind() {
		let memo = RcTryLazy::catch_unwind(|| {
			if true {
				panic!("oops")
			}
			42
		});

		match memo.evaluate() {
			Err(e) => assert_eq!(e, "oops"),
			Ok(_) => panic!("Should have failed"),
		}
	}

	/// Tests creation from `TryThunk`.
	#[test]
	fn test_try_memo_from_try_eval() {
		let eval = TryThunk::new(|| Ok::<i32, ()>(42));
		let memo = RcTryLazy::from(eval);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests creation from `TryTrampoline`.
	#[test]
	fn test_try_memo_from_try_task() {
		let task = TryTrampoline::<i32, ()>::ok(42);
		let memo = RcTryLazy::from(task);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests conversion to TryLazy.
	#[test]
	fn test_try_memo_from_rc_memo() {
		let memo = RcLazy::new(|| 42);
		let try_memo: crate::types::RcTryLazy<i32, ()> = crate::types::RcTryLazy::from(memo);
		assert_eq!(try_memo.evaluate(), Ok(&42));
	}

	/// Tests conversion to ArcTryLazy.
	#[test]
	fn test_try_memo_from_arc_memo() {
		use crate::types::ArcLazy;
		let memo = ArcLazy::new(|| 42);
		let try_memo: crate::types::ArcTryLazy<i32, ()> = crate::types::ArcTryLazy::from(memo);
		assert_eq!(try_memo.evaluate(), Ok(&42));
	}

	/// Tests SendDefer implementation.
	#[test]
	fn test_send_defer() {
		use crate::classes::send_deferrable::send_defer;

		let memo: ArcTryLazy<i32, ()> = send_defer(|| ArcTryLazy::new(|| Ok(42)));
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `RcTryLazy::ok` convenience constructor.
	#[test]
	fn test_rc_try_lazy_ok() {
		let memo = RcTryLazy::<i32, ()>::ok(42);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `RcTryLazy::err` convenience constructor.
	#[test]
	fn test_rc_try_lazy_err() {
		let memo = RcTryLazy::<i32, String>::err("error".to_string());
		assert_eq!(memo.evaluate(), Err(&"error".to_string()));
	}

	/// Tests `ArcTryLazy::ok` convenience constructor.
	#[test]
	fn test_arc_try_lazy_ok() {
		let memo = ArcTryLazy::<i32, ()>::ok(42);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `ArcTryLazy::err` convenience constructor.
	#[test]
	fn test_arc_try_lazy_err() {
		let memo = ArcTryLazy::<i32, String>::err("error".to_string());
		assert_eq!(memo.evaluate(), Err(&"error".to_string()));
	}

	/// Tests `From<Result>` for `RcTryLazy` with `Ok`.
	#[test]
	fn test_rc_try_lazy_from_result_ok() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::from(Ok(42));
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `From<Result>` for `RcTryLazy` with `Err`.
	#[test]
	fn test_rc_try_lazy_from_result_err() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::from(Err("error".to_string()));
		assert_eq!(memo.evaluate(), Err(&"error".to_string()));
	}

	/// Tests `From<Result>` for `ArcTryLazy` with `Ok`.
	#[test]
	fn test_arc_try_lazy_from_result_ok() {
		let memo: ArcTryLazy<i32, String> = ArcTryLazy::from(Ok(42));
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `From<Result>` for `ArcTryLazy` with `Err`.
	#[test]
	fn test_arc_try_lazy_from_result_err() {
		let memo: ArcTryLazy<i32, String> = ArcTryLazy::from(Err("error".to_string()));
		assert_eq!(memo.evaluate(), Err(&"error".to_string()));
	}

	/// Tests that a panicking initializer poisons the RcTryLazy.
	///
	/// Verifies that subsequent evaluate calls also panic after
	/// the initializer panics.
	#[test]
	fn test_panic_poisoning() {
		use std::panic;

		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| {
			panic!("initializer panic");
		});

		let result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
			let _ = memo.evaluate();
		}));
		assert!(result.is_err(), "First evaluate should panic");

		let result2 = panic::catch_unwind(panic::AssertUnwindSafe(|| {
			let _ = memo.evaluate();
		}));
		assert!(result2.is_err(), "Second evaluate should also panic (poisoned)");
	}

	/// Tests that ArcTryLazy is thread-safe.
	///
	/// Spawns 10 threads sharing an ArcTryLazy and verifies the
	/// computation runs exactly once.
	#[test]
	fn test_arc_try_lazy_thread_safety() {
		use std::{
			sync::atomic::{
				AtomicUsize,
				Ordering,
			},
			thread,
		};

		let counter = Arc::new(AtomicUsize::new(0));
		let counter_clone = counter.clone();
		let memo: ArcTryLazy<i32, String> = ArcTryLazy::new(move || {
			counter_clone.fetch_add(1, Ordering::SeqCst);
			Ok(42)
		});

		let mut handles = vec![];
		for _ in 0 .. 10 {
			let memo_clone = memo.clone();
			handles.push(thread::spawn(move || {
				assert_eq!(memo_clone.evaluate(), Ok(&42));
			}));
		}

		for handle in handles {
			handle.join().unwrap();
		}

		assert_eq!(counter.load(Ordering::SeqCst), 1);
	}

	/// Memoization: evaluating twice returns the same value.
	#[quickcheck]
	fn memoization_ok(x: i32) -> bool {
		let memo: RcTryLazy<i32, i32> = RcTryLazy::new(move || Ok(x));
		let first = memo.evaluate();
		let second = memo.evaluate();
		first == second && first == Ok(&x)
	}

	/// Error memoization: error values are cached correctly.
	#[quickcheck]
	fn memoization_err(e: i32) -> bool {
		let memo: RcTryLazy<i32, i32> = RcTryLazy::new(move || Err(e));
		let first = memo.evaluate();
		let second = memo.evaluate();
		first == second && first == Err(&e)
	}

	/// Deferrable transparency: `send_defer(|| x).evaluate() == x.evaluate()`.
	#[quickcheck]
	fn deferrable_transparency(x: i32) -> bool {
		use crate::classes::send_deferrable::send_defer;

		let memo: ArcTryLazy<i32, i32> = ArcTryLazy::new(move || Ok(x));
		let deferred: ArcTryLazy<i32, i32> = send_defer(move || ArcTryLazy::new(move || Ok(x)));
		memo.evaluate() == deferred.evaluate()
	}

	/// Tests `ArcTryLazy::catch_unwind` with a panicking closure.
	///
	/// Verifies that panics are caught and converted to errors.
	#[test]
	fn test_arc_catch_unwind() {
		let memo = ArcTryLazy::catch_unwind(|| {
			if true {
				panic!("oops")
			}
			42
		});

		match memo.evaluate() {
			Err(e) => assert_eq!(e, "oops"),
			Ok(_) => panic!("Should have failed"),
		}
	}

	/// Tests `ArcTryLazy::catch_unwind` with a non-panicking closure.
	///
	/// Verifies that a successful closure wraps the value in `Ok`.
	#[test]
	fn test_arc_catch_unwind_success() {
		let memo = ArcTryLazy::catch_unwind(|| 42);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `RcTryLazy::catch_unwind_with` with a panicking closure.
	///
	/// Verifies that the custom handler converts the panic payload.
	#[test]
	fn test_rc_catch_unwind_with_panic() {
		let memo = RcTryLazy::<i32, i32>::catch_unwind_with(
			|| {
				if true {
					panic!("oops")
				}
				42
			},
			|_payload| -1,
		);
		assert_eq!(memo.evaluate(), Err(&-1));
	}

	/// Tests `RcTryLazy::catch_unwind_with` with a non-panicking closure.
	///
	/// Verifies that a successful closure wraps the value in `Ok`.
	#[test]
	fn test_rc_catch_unwind_with_success() {
		let memo = RcTryLazy::<i32, i32>::catch_unwind_with(|| 42, |_payload| -1);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `ArcTryLazy::catch_unwind_with` with a panicking closure.
	///
	/// Verifies that the custom handler converts the panic payload.
	#[test]
	fn test_arc_catch_unwind_with_panic() {
		let memo = ArcTryLazy::<i32, i32>::catch_unwind_with(
			|| {
				if true {
					panic!("oops")
				}
				42
			},
			|_payload| -1,
		);
		assert_eq!(memo.evaluate(), Err(&-1));
	}

	/// Tests `ArcTryLazy::catch_unwind_with` with a non-panicking closure.
	///
	/// Verifies that a successful closure wraps the value in `Ok`.
	#[test]
	fn test_arc_catch_unwind_with_success() {
		let memo = ArcTryLazy::<i32, i32>::catch_unwind_with(|| 42, |_payload| -1);
		assert_eq!(memo.evaluate(), Ok(&42));
	}

	/// Tests `RcTryLazy::map` with a successful value.
	///
	/// Verifies that `map` transforms the cached success value.
	#[test]
	fn test_rc_try_lazy_map_ok() {
		let memo = RcTryLazy::<i32, String>::ok(10);
		let mapped = memo.map(|a| a * 2);
		assert_eq!(mapped.evaluate(), Ok(&20));
	}

	/// Tests `RcTryLazy::map` with an error value.
	///
	/// Verifies that `map` propagates the error without calling the function.
	#[test]
	fn test_rc_try_lazy_map_err() {
		let memo = RcTryLazy::<i32, String>::err("error".to_string());
		let mapped = memo.map(|a| a * 2);
		assert_eq!(mapped.evaluate(), Err(&"error".to_string()));
	}

	/// Tests `RcTryLazy::map_err` with an error value.
	///
	/// Verifies that `map_err` transforms the cached error value.
	#[test]
	fn test_rc_try_lazy_map_err_err() {
		let memo = RcTryLazy::<i32, String>::err("error".to_string());
		let mapped = memo.map_err(|e| format!("wrapped: {}", e));
		assert_eq!(mapped.evaluate(), Err(&"wrapped: error".to_string()));
	}

	/// Tests `RcTryLazy::map_err` with a successful value.
	///
	/// Verifies that `map_err` propagates the success without calling the function.
	#[test]
	fn test_rc_try_lazy_map_err_ok() {
		let memo = RcTryLazy::<i32, String>::ok(42);
		let mapped = memo.map_err(|e| format!("wrapped: {}", e));
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	/// Tests `RcTryLazy::bimap` with a successful value.
	///
	/// Verifies that `bimap` transforms the success value via `f`.
	#[test]
	fn test_rc_try_lazy_bimap_ok() {
		let memo = RcTryLazy::<i32, String>::ok(10);
		let mapped = memo.bimap(|a| a * 2, |e| e.len());
		assert_eq!(mapped.evaluate(), Ok(&20));
	}

	/// Tests `RcTryLazy::bimap` with an error value.
	///
	/// Verifies that `bimap` transforms the error value via `g`.
	#[test]
	fn test_rc_try_lazy_bimap_err() {
		let memo = RcTryLazy::<i32, String>::err("error".to_string());
		let mapped = memo.bimap(|a| a * 2, |e| e.len());
		assert_eq!(mapped.evaluate(), Err(&5));
	}

	/// Tests `ArcTryLazy::map` with a successful value.
	///
	/// Verifies that `map` transforms the cached success value.
	#[test]
	fn test_arc_try_lazy_map_ok() {
		let memo = ArcTryLazy::<i32, String>::ok(10);
		let mapped = memo.map(|a| a * 2);
		assert_eq!(mapped.evaluate(), Ok(&20));
	}

	/// Tests `ArcTryLazy::map` with an error value.
	///
	/// Verifies that `map` propagates the error without calling the function.
	#[test]
	fn test_arc_try_lazy_map_err() {
		let memo = ArcTryLazy::<i32, String>::err("error".to_string());
		let mapped = memo.map(|a| a * 2);
		assert_eq!(mapped.evaluate(), Err(&"error".to_string()));
	}

	/// Tests `ArcTryLazy::map_err` with an error value.
	///
	/// Verifies that `map_err` transforms the cached error value.
	#[test]
	fn test_arc_try_lazy_map_err_err() {
		let memo = ArcTryLazy::<i32, String>::err("error".to_string());
		let mapped = memo.map_err(|e| format!("wrapped: {}", e));
		assert_eq!(mapped.evaluate(), Err(&"wrapped: error".to_string()));
	}

	/// Tests `ArcTryLazy::map_err` with a successful value.
	///
	/// Verifies that `map_err` propagates the success without calling the function.
	#[test]
	fn test_arc_try_lazy_map_err_ok() {
		let memo = ArcTryLazy::<i32, String>::ok(42);
		let mapped = memo.map_err(|e| format!("wrapped: {}", e));
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	/// Tests `ArcTryLazy::bimap` with a successful value.
	///
	/// Verifies that `bimap` transforms the success value via `f`.
	#[test]
	fn test_arc_try_lazy_bimap_ok() {
		let memo = ArcTryLazy::<i32, String>::ok(10);
		let mapped = memo.bimap(|a| a * 2, |e| e.len());
		assert_eq!(mapped.evaluate(), Ok(&20));
	}

	/// Tests `ArcTryLazy::bimap` with an error value.
	///
	/// Verifies that `bimap` transforms the error value via `g`.
	#[test]
	fn test_arc_try_lazy_bimap_err() {
		let memo = ArcTryLazy::<i32, String>::err("error".to_string());
		let mapped = memo.bimap(|a| a * 2, |e| e.len());
		assert_eq!(mapped.evaluate(), Err(&5));
	}

	// -- RefFunctor tests --

	/// Tests `RefFunctor::ref_map` on `RcTryLazy` with a successful value.
	#[test]
	fn test_ref_functor_rc_try_lazy_ok() {
		use crate::{
			brands::TryLazyBrand,
			classes::RefFunctor,
		};
		let memo = RcTryLazy::<i32, String>::ok(10);
		let mapped = TryLazyBrand::<String, RcLazyConfig>::ref_map(|x: &i32| *x * 3, &memo);
		assert_eq!(mapped.evaluate(), Ok(&30));
	}

	/// Tests `RefFunctor::ref_map` on `RcTryLazy` with an error value.
	#[test]
	fn test_ref_functor_rc_try_lazy_err() {
		use crate::{
			brands::TryLazyBrand,
			classes::RefFunctor,
		};
		let memo = RcTryLazy::<i32, String>::err("fail".to_string());
		let mapped = TryLazyBrand::<String, RcLazyConfig>::ref_map(|x: &i32| *x * 3, &memo);
		assert_eq!(mapped.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests `RefFunctor` identity law for `RcTryLazy`.
	#[test]
	fn test_ref_functor_rc_try_lazy_identity() {
		use crate::{
			brands::TryLazyBrand,
			classes::RefFunctor,
		};
		let memo = RcTryLazy::<i32, String>::ok(42);
		let mapped = TryLazyBrand::<String, RcLazyConfig>::ref_map(|x: &i32| *x, &memo.clone());
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	// -- SendRefFunctor tests --

	/// Tests `SendRefFunctor::send_ref_map` on `ArcTryLazy` with a successful value.
	#[test]
	fn test_send_ref_functor_arc_try_lazy_ok() {
		use crate::{
			brands::TryLazyBrand,
			classes::SendRefFunctor,
		};
		let memo = ArcTryLazy::<i32, String>::ok(10);
		let mapped = TryLazyBrand::<String, ArcLazyConfig>::send_ref_map(|x: &i32| *x * 3, &memo);
		assert_eq!(mapped.evaluate(), Ok(&30));
	}

	/// Tests `SendRefFunctor::send_ref_map` on `ArcTryLazy` with an error value.
	#[test]
	fn test_send_ref_functor_arc_try_lazy_err() {
		use crate::{
			brands::TryLazyBrand,
			classes::SendRefFunctor,
		};
		let memo = ArcTryLazy::<i32, String>::err("fail".to_string());
		let mapped = TryLazyBrand::<String, ArcLazyConfig>::send_ref_map(|x: &i32| *x * 3, &memo);
		assert_eq!(mapped.evaluate(), Err(&"fail".to_string()));
	}

	// -- Inherent ref_map tests --

	/// Tests `RcTryLazy::ref_map` with a successful value.
	#[test]
	fn test_rc_try_lazy_ref_map_ok() {
		let memo = RcTryLazy::<i32, String>::ok(10);
		let mapped = memo.ref_map(|x| *x * 2);
		assert_eq!(mapped.evaluate(), Ok(&20));
	}

	/// Tests `RcTryLazy::ref_map` with an error value.
	#[test]
	fn test_rc_try_lazy_ref_map_err() {
		let memo = RcTryLazy::<i32, String>::err("fail".to_string());
		let mapped = memo.ref_map(|x| *x * 2);
		assert_eq!(mapped.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests `RcTryLazy::ref_map` identity law.
	#[test]
	fn test_rc_try_lazy_ref_map_identity() {
		let memo = RcTryLazy::<i32, String>::ok(42);
		let mapped = memo.ref_map(|x| *x);
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	/// Tests `ArcTryLazy::ref_map` with a successful value.
	#[test]
	fn test_arc_try_lazy_ref_map_ok() {
		let memo = ArcTryLazy::<i32, String>::ok(10);
		let mapped = memo.ref_map(|x| *x * 2);
		assert_eq!(mapped.evaluate(), Ok(&20));
	}

	/// Tests `ArcTryLazy::ref_map` with an error value.
	#[test]
	fn test_arc_try_lazy_ref_map_err() {
		let memo = ArcTryLazy::<i32, String>::err("fail".to_string());
		let mapped = memo.ref_map(|x| *x * 2);
		assert_eq!(mapped.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests `ArcTryLazy::ref_map` identity law.
	#[test]
	fn test_arc_try_lazy_ref_map_identity() {
		let memo = ArcTryLazy::<i32, String>::ok(42);
		let mapped = memo.ref_map(|x| *x);
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	// -- Semigroup tests --

	/// Tests `Semigroup::append` for `RcTryLazy` when both are `Ok`.
	#[test]
	fn test_semigroup_rc_try_lazy_both_ok() {
		use crate::functions::append;
		let a = RcTryLazy::<String, String>::ok("Hello".to_string());
		let b = RcTryLazy::<String, String>::ok(" World".to_string());
		let c = append(a, b);
		assert_eq!(c.evaluate(), Ok(&"Hello World".to_string()));
	}

	/// Tests `Semigroup::append` for `RcTryLazy` when the first is `Err`.
	#[test]
	fn test_semigroup_rc_try_lazy_first_err() {
		use crate::functions::append;
		let a = RcTryLazy::<String, String>::err("err1".to_string());
		let b = RcTryLazy::<String, String>::ok("ok".to_string());
		let c = append(a, b);
		assert_eq!(c.evaluate(), Err(&"err1".to_string()));
	}

	/// Tests `Semigroup::append` for `RcTryLazy` when the second is `Err`.
	#[test]
	fn test_semigroup_rc_try_lazy_second_err() {
		use crate::functions::append;
		let a = RcTryLazy::<String, String>::ok("ok".to_string());
		let b = RcTryLazy::<String, String>::err("err2".to_string());
		let c = append(a, b);
		assert_eq!(c.evaluate(), Err(&"err2".to_string()));
	}

	/// Tests `Semigroup::append` for `ArcTryLazy` when both are `Ok`.
	#[test]
	fn test_semigroup_arc_try_lazy_both_ok() {
		use crate::functions::append;
		let a = ArcTryLazy::<String, String>::ok("Hello".to_string());
		let b = ArcTryLazy::<String, String>::ok(" World".to_string());
		let c = append(a, b);
		assert_eq!(c.evaluate(), Ok(&"Hello World".to_string()));
	}

	/// Tests `Semigroup::append` for `ArcTryLazy` when the first is `Err`.
	#[test]
	fn test_semigroup_arc_try_lazy_first_err() {
		use crate::functions::append;
		let a = ArcTryLazy::<String, String>::err("err1".to_string());
		let b = ArcTryLazy::<String, String>::ok("ok".to_string());
		let c = append(a, b);
		assert_eq!(c.evaluate(), Err(&"err1".to_string()));
	}

	// -- Monoid tests --

	/// Tests `Monoid::empty` for `RcTryLazy`.
	#[test]
	fn test_monoid_rc_try_lazy_empty() {
		use crate::functions::empty;
		let t: RcTryLazy<String, ()> = empty();
		assert_eq!(t.evaluate(), Ok(&String::new()));
	}

	/// Tests `Monoid::empty` for `ArcTryLazy`.
	#[test]
	fn test_monoid_arc_try_lazy_empty() {
		use crate::functions::empty;
		let t: ArcTryLazy<String, ()> = empty();
		assert_eq!(t.evaluate(), Ok(&String::new()));
	}

	/// Tests monoid left identity for `RcTryLazy`.
	#[test]
	fn test_monoid_rc_try_lazy_left_identity() {
		use crate::functions::{
			append,
			empty,
		};
		let a = RcTryLazy::<String, ()>::ok("hello".to_string());
		let result = append(empty::<RcTryLazy<String, ()>>(), a);
		assert_eq!(result.evaluate(), Ok(&"hello".to_string()));
	}

	/// Tests monoid right identity for `RcTryLazy`.
	#[test]
	fn test_monoid_rc_try_lazy_right_identity() {
		use crate::functions::{
			append,
			empty,
		};
		let a = RcTryLazy::<String, ()>::ok("hello".to_string());
		let result = append(a, empty::<RcTryLazy<String, ()>>());
		assert_eq!(result.evaluate(), Ok(&"hello".to_string()));
	}

	// -- Foldable tests --

	/// Tests `Foldable::fold_right` for `RcTryLazy` with `Ok`.
	#[test]
	fn test_foldable_rc_try_lazy_fold_right_ok() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = RcTryLazy::<i32, String>::ok(10);
		let result = explicit::fold_right::<
			crate::brands::RcFnBrand,
			TryLazyBrand<String, RcLazyConfig>,
			_,
			_,
			_,
			_,
		>(|a: &i32, b| *a + b, 5, &lazy);
		assert_eq!(result, 15);
	}

	/// Tests `Foldable::fold_right` for `RcTryLazy` with `Err`.
	#[test]
	fn test_foldable_rc_try_lazy_fold_right_err() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = RcTryLazy::<i32, String>::err("fail".to_string());
		let result = explicit::fold_right::<
			crate::brands::RcFnBrand,
			TryLazyBrand<String, RcLazyConfig>,
			_,
			_,
			_,
			_,
		>(|a: &i32, b| *a + b, 5, &lazy);
		assert_eq!(result, 5);
	}

	/// Tests `Foldable::fold_left` for `RcTryLazy` with `Ok`.
	#[test]
	fn test_foldable_rc_try_lazy_fold_left_ok() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = RcTryLazy::<i32, String>::ok(10);
		let result = explicit::fold_left::<
			crate::brands::RcFnBrand,
			TryLazyBrand<String, RcLazyConfig>,
			_,
			_,
			_,
			_,
		>(|b, a: &i32| b + *a, 5, &lazy);
		assert_eq!(result, 15);
	}

	/// Tests `Foldable::fold_left` for `RcTryLazy` with `Err`.
	#[test]
	fn test_foldable_rc_try_lazy_fold_left_err() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = RcTryLazy::<i32, String>::err("fail".to_string());
		let result = explicit::fold_left::<
			crate::brands::RcFnBrand,
			TryLazyBrand<String, RcLazyConfig>,
			_,
			_,
			_,
			_,
		>(|b, a: &i32| b + *a, 5, &lazy);
		assert_eq!(result, 5);
	}

	/// Tests `Foldable::fold_map` for `RcTryLazy` with `Ok`.
	#[test]
	fn test_foldable_rc_try_lazy_fold_map_ok() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = RcTryLazy::<i32, String>::ok(10);
		let result = explicit::fold_map::<RcFnBrand, TryLazyBrand<String, RcLazyConfig>, _, _, _, _>(
			|a: &i32| a.to_string(),
			&lazy,
		);
		assert_eq!(result, "10");
	}

	/// Tests `Foldable::fold_map` for `RcTryLazy` with `Err`.
	#[test]
	fn test_foldable_rc_try_lazy_fold_map_err() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = RcTryLazy::<i32, String>::err("fail".to_string());
		let result = explicit::fold_map::<RcFnBrand, TryLazyBrand<String, RcLazyConfig>, _, _, _, _>(
			|a: &i32| a.to_string(),
			&lazy,
		);
		assert_eq!(result, "");
	}

	/// Tests `Foldable::fold_right` for `ArcTryLazy` with `Ok`.
	#[test]
	fn test_foldable_arc_try_lazy_fold_right_ok() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = ArcTryLazy::<i32, String>::ok(10);
		let result = explicit::fold_right::<
			crate::brands::ArcFnBrand,
			TryLazyBrand<String, ArcLazyConfig>,
			_,
			_,
			_,
			_,
		>(|a: &i32, b| *a + b, 5, &lazy);
		assert_eq!(result, 15);
	}

	/// Tests `Foldable::fold_right` for `ArcTryLazy` with `Err`.
	#[test]
	fn test_foldable_arc_try_lazy_fold_right_err() {
		use crate::{
			brands::*,
			functions::*,
		};

		let lazy = ArcTryLazy::<i32, String>::err("fail".to_string());
		let result = explicit::fold_right::<
			crate::brands::ArcFnBrand,
			TryLazyBrand<String, ArcLazyConfig>,
			_,
			_,
			_,
			_,
		>(|a: &i32, b| *a + b, 5, &lazy);
		assert_eq!(result, 5);
	}

	// -- FoldableWithIndex tests --

	/// Tests `ref_fold_map_with_index` for `RcTryLazy` with `Ok`.
	///
	/// Verifies that the index is `()` and the value is folded correctly.
	#[test]
	fn test_rc_try_lazy_ref_fold_map_with_index_ok() {
		use crate::classes::ref_foldable_with_index::RefFoldableWithIndex;

		let lazy = RcTryLazy::<i32, ()>::ok(42);
		let result =
			<TryLazyBrand<(), RcLazyConfig> as RefFoldableWithIndex>::ref_fold_map_with_index::<
				RcFnBrand,
				_,
				_,
			>(|_, x: &i32| x.to_string(), &lazy);
		assert_eq!(result, "42");
	}

	/// Tests `ref_fold_map_with_index` for `RcTryLazy` with `Err`.
	///
	/// Verifies that the monoid identity is returned when the computation fails.
	#[test]
	fn test_rc_try_lazy_ref_fold_map_with_index_err() {
		use crate::classes::ref_foldable_with_index::RefFoldableWithIndex;

		let lazy = RcTryLazy::<i32, String>::err("fail".to_string());
		let result =
			<TryLazyBrand<String, RcLazyConfig> as RefFoldableWithIndex>::ref_fold_map_with_index::<
				RcFnBrand,
				_,
				_,
			>(|_, x: &i32| x.to_string(), &lazy);
		assert_eq!(result, "");
	}

	/// Tests `ref_fold_map_with_index` for `ArcTryLazy` with `Ok`.
	///
	/// Verifies that the index is `()` and the value is folded correctly.
	#[test]
	fn test_arc_try_lazy_ref_fold_map_with_index_ok() {
		use crate::classes::ref_foldable_with_index::RefFoldableWithIndex;

		let lazy = ArcTryLazy::<i32, ()>::ok(10);
		let result =
			<TryLazyBrand<(), ArcLazyConfig> as RefFoldableWithIndex>::ref_fold_map_with_index::<
				RcFnBrand,
				_,
				_,
			>(|_, x: &i32| x.to_string(), &lazy);
		assert_eq!(result, "10");
	}

	/// Tests `ref_fold_map_with_index` for `ArcTryLazy` with `Err`.
	///
	/// Verifies that the monoid identity is returned when the computation fails.
	#[test]
	fn test_arc_try_lazy_ref_fold_map_with_index_err() {
		use crate::classes::ref_foldable_with_index::RefFoldableWithIndex;

		let lazy = ArcTryLazy::<i32, String>::err("fail".to_string());
		let result =
			<TryLazyBrand<String, ArcLazyConfig> as RefFoldableWithIndex>::ref_fold_map_with_index::<
				RcFnBrand,
				_,
				_,
			>(|_, x: &i32| x.to_string(), &lazy);
		assert_eq!(result, "");
	}

	/// Tests compatibility of `FoldableWithIndex` with `Foldable`.
	///
	/// Verifies that `fold_map(f, fa) == ref_fold_map_with_index(|_, a| f(a), fa)`.
	#[test]
	fn test_rc_try_lazy_foldable_with_index_compatibility() {
		use crate::{
			brands::*,
			classes::ref_foldable_with_index::RefFoldableWithIndex,
			functions::*,
		};

		let lazy1 = RcTryLazy::<i32, ()>::ok(7);
		let lazy2 = RcTryLazy::<i32, ()>::ok(7);

		let fold_result = explicit::fold_map::<RcFnBrand, TryLazyBrand<(), RcLazyConfig>, _, _, _, _>(
			|a: &i32| a.to_string(),
			&lazy1,
		);
		let fold_with_index_result =
			<TryLazyBrand<(), RcLazyConfig> as RefFoldableWithIndex>::ref_fold_map_with_index::<
				RcFnBrand,
				_,
				_,
			>(|_, a| a.to_string(), &lazy2);
		assert_eq!(fold_result, fold_with_index_result);
	}

	/// Tests `Semigroup::append` where the first operand is `Err`.
	///
	/// Verifies that the second operand is not evaluated (short-circuit behavior).
	#[test]
	fn test_semigroup_append_first_err_short_circuits() {
		use {
			crate::classes::Semigroup,
			std::cell::Cell,
		};

		let counter = Rc::new(Cell::new(0u32));
		let counter_clone = counter.clone();

		let a: RcTryLazy<String, String> = RcTryLazy::new(|| Err("first failed".into()));
		let b: RcTryLazy<String, String> = RcTryLazy::new(move || {
			counter_clone.set(counter_clone.get() + 1);
			Ok("second".into())
		});

		let result = Semigroup::append(a, b);
		assert_eq!(result.evaluate(), Err(&"first failed".to_string()));
		assert_eq!(counter.get(), 0, "second operand should not be evaluated");
	}

	/// Tests `Semigroup::append` where the second operand fails but the first succeeds.
	///
	/// Verifies that the error from the second operand is propagated.
	#[test]
	fn test_semigroup_append_second_err() {
		use crate::classes::Semigroup;

		let a: RcTryLazy<String, String> = RcTryLazy::new(|| Ok("hello".into()));
		let b: RcTryLazy<String, String> = RcTryLazy::new(|| Err("second failed".into()));

		let result = Semigroup::append(a, b);
		assert_eq!(result.evaluate(), Err(&"second failed".to_string()));
	}

	/// Tests `Semigroup::append` where both operands succeed.
	#[test]
	fn test_semigroup_append_both_ok() {
		use crate::classes::Semigroup;

		let a: RcTryLazy<String, ()> = RcTryLazy::new(|| Ok("Hello".into()));
		let b: RcTryLazy<String, ()> = RcTryLazy::new(|| Ok(" World".into()));

		let result = Semigroup::append(a, b);
		assert_eq!(result.evaluate(), Ok(&"Hello World".to_string()));
	}

	/// Tests `map` on a successful `TryLazy`.
	#[test]
	fn test_map_ok() {
		let memo = RcTryLazy::new(|| Ok::<i32, ()>(21));
		let mapped = memo.map(|x| x * 2);
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	/// Tests `map` on a failed `TryLazy`.
	#[test]
	fn test_map_err() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Err("oops".into()));
		let mapped = memo.map(|x| x * 2);
		assert_eq!(mapped.evaluate(), Err(&"oops".to_string()));
	}

	/// Tests `map_err` on a failed `TryLazy`.
	#[test]
	fn test_map_err_on_err() {
		let memo: RcTryLazy<i32, i32> = RcTryLazy::new(|| Err(21));
		let mapped = memo.map_err(|e| e * 2);
		assert_eq!(mapped.evaluate(), Err(&42));
	}

	/// Tests `map_err` on a successful `TryLazy`.
	#[test]
	fn test_map_err_on_ok() {
		let memo: RcTryLazy<i32, i32> = RcTryLazy::new(|| Ok(42));
		let mapped = memo.map_err(|e| e * 2);
		assert_eq!(mapped.evaluate(), Ok(&42));
	}

	/// Tests `and_then` on a successful `TryLazy`.
	#[test]
	fn test_and_then_ok() {
		let memo = RcTryLazy::new(|| Ok::<i32, String>(21));
		let chained = memo.and_then(|x| Ok(x * 2));
		assert_eq!(chained.evaluate(), Ok(&42));
	}

	/// Tests `and_then` where the chained operation fails.
	#[test]
	fn test_and_then_chained_err() {
		let memo = RcTryLazy::new(|| Ok::<i32, String>(21));
		let chained = memo.and_then(|_: &i32| Err::<i32, String>("chained failure".into()));
		assert_eq!(chained.evaluate(), Err(&"chained failure".to_string()));
	}

	/// Tests `and_then` on a failed `TryLazy`.
	#[test]
	fn test_and_then_initial_err() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Err("initial".into()));
		let chained = memo.and_then(|x| Ok(x * 2));
		assert_eq!(chained.evaluate(), Err(&"initial".to_string()));
	}

	/// Tests `or_else` on a failed `TryLazy`.
	#[test]
	fn test_or_else_recovers() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Err("oops".into()));
		let recovered = memo.or_else(|_| Ok(42));
		assert_eq!(recovered.evaluate(), Ok(&42));
	}

	/// Tests `or_else` on a successful `TryLazy`.
	#[test]
	fn test_or_else_noop_on_ok() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Ok(42));
		let recovered = memo.or_else(|_| Ok(99));
		assert_eq!(recovered.evaluate(), Ok(&42));
	}

	/// Tests `or_else` where recovery itself fails.
	#[test]
	fn test_or_else_recovery_fails() {
		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Err("first".into()));
		let recovered = memo.or_else(|_| Err("second".into()));
		assert_eq!(recovered.evaluate(), Err(&"second".to_string()));
	}

	/// Tests `Foldable` fold_right on a successful `TryLazy`.
	#[test]
	fn test_foldable_ok() {
		use crate::{
			brands::*,
			functions::*,
		};

		let memo: RcTryLazy<i32, ()> = RcTryLazy::new(|| Ok(10));
		let result = explicit::fold_right::<RcFnBrand, TryLazyBrand<(), RcLazyConfig>, _, _, _, _>(
			|a: &i32, b| *a + b,
			5,
			&memo,
		);
		assert_eq!(result, 15);
	}

	/// Tests `Foldable` fold_right on a failed `TryLazy`.
	#[test]
	fn test_foldable_err() {
		use crate::{
			brands::*,
			functions::*,
		};

		let memo: RcTryLazy<i32, String> = RcTryLazy::new(|| Err("oops".into()));
		let result =
			explicit::fold_right::<RcFnBrand, TryLazyBrand<String, RcLazyConfig>, _, _, _, _>(
				|a: &i32, b| *a + b,
				5,
				&memo,
			);
		assert_eq!(result, 5);
	}

	/// Tests `From<TrySendThunk> for ArcTryLazy` with a successful thunk.
	#[test]
	fn test_from_try_send_thunk_ok() {
		let counter = Arc::new(std::sync::atomic::AtomicUsize::new(0));
		let counter_clone = counter.clone();
		let thunk: TrySendThunk<i32, ()> = TrySendThunk::new(move || {
			counter_clone.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
			Ok(42)
		});

		// Conversion should not evaluate eagerly.
		assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 0);

		let lazy: ArcTryLazy<i32, ()> = ArcTryLazy::from(thunk);
		assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 0);

		// First access triggers evaluation.
		assert_eq!(lazy.evaluate(), Ok(&42));
		assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);

		// Second access uses cached result.
		assert_eq!(lazy.evaluate(), Ok(&42));
		assert_eq!(counter.load(std::sync::atomic::Ordering::SeqCst), 1);
	}

	/// Tests `From<TrySendThunk> for ArcTryLazy` with a failing thunk.
	#[test]
	fn test_from_try_send_thunk_err() {
		let thunk: TrySendThunk<i32, String> = TrySendThunk::new(move || Err("fail".to_string()));
		let lazy: ArcTryLazy<i32, String> = ArcTryLazy::from(thunk);
		assert_eq!(lazy.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests that `Into<ArcTryLazy>` works for `TrySendThunk`.
	#[test]
	fn test_try_send_thunk_into_arc_try_lazy() {
		let thunk: TrySendThunk<i32, ()> = TrySendThunk::ok(42);
		let lazy: ArcTryLazy<i32, ()> = thunk.into();
		assert_eq!(lazy.evaluate(), Ok(&42));
	}

	// -- PartialEq tests --

	/// Tests `PartialEq` for equal `Ok` values.
	#[test]
	fn test_try_lazy_partial_eq_ok() {
		let a = RcTryLazy::<i32, ()>::ok(42);
		let b = RcTryLazy::<i32, ()>::ok(42);
		assert_eq!(a, b);
	}

	/// Tests `PartialEq` for unequal `Ok` values.
	#[test]
	fn test_try_lazy_partial_eq_ok_neq() {
		let a = RcTryLazy::<i32, ()>::ok(1);
		let b = RcTryLazy::<i32, ()>::ok(2);
		assert_ne!(a, b);
	}

	/// Tests `PartialEq` for equal `Err` values.
	#[test]
	fn test_try_lazy_partial_eq_err() {
		let a = RcTryLazy::<i32, String>::err("fail".to_string());
		let b = RcTryLazy::<i32, String>::err("fail".to_string());
		assert_eq!(a, b);
	}

	/// Tests `PartialEq` for `Ok` vs `Err`.
	#[test]
	fn test_try_lazy_partial_eq_ok_vs_err() {
		let a = RcTryLazy::<i32, i32>::ok(1);
		let b = RcTryLazy::<i32, i32>::err(1);
		assert_ne!(a, b);
	}

	/// Tests `PartialEq` for `ArcTryLazy`.
	#[test]
	fn test_try_lazy_partial_eq_arc() {
		let a = ArcTryLazy::<i32, ()>::ok(42);
		let b = ArcTryLazy::<i32, ()>::ok(42);
		assert_eq!(a, b);
	}

	// -- Hash tests --

	/// Tests that equal `TryLazy` values produce equal hashes.
	#[test]
	fn test_try_lazy_hash_eq() {
		use std::{
			collections::hash_map::DefaultHasher,
			hash::{
				Hash,
				Hasher,
			},
		};

		let a = RcTryLazy::<i32, ()>::ok(42);
		let b = RcTryLazy::<i32, ()>::ok(42);

		let mut h1 = DefaultHasher::new();
		a.hash(&mut h1);
		let mut h2 = DefaultHasher::new();
		b.hash(&mut h2);

		assert_eq!(h1.finish(), h2.finish());
	}

	/// Tests that `TryLazy` hash matches the underlying `Result` hash.
	#[test]
	fn test_try_lazy_hash_matches_result() {
		use std::{
			collections::hash_map::DefaultHasher,
			hash::{
				Hash,
				Hasher,
			},
		};

		let lazy = RcTryLazy::<i32, ()>::ok(42);
		let mut h1 = DefaultHasher::new();
		lazy.hash(&mut h1);

		let result: Result<i32, ()> = Ok(42);
		let mut h2 = DefaultHasher::new();
		result.hash(&mut h2);

		assert_eq!(h1.finish(), h2.finish());
	}

	// -- PartialOrd tests --

	/// Tests `PartialOrd` for `Ok` values.
	#[test]
	fn test_try_lazy_partial_ord_ok() {
		let a = RcTryLazy::<i32, ()>::ok(1);
		let b = RcTryLazy::<i32, ()>::ok(2);
		assert!(a < b);
		assert!(b > a);
	}

	/// Tests `PartialOrd` for equal values.
	#[test]
	fn test_try_lazy_partial_ord_eq() {
		let a = RcTryLazy::<i32, ()>::ok(42);
		let b = RcTryLazy::<i32, ()>::ok(42);
		assert!(a <= b);
		assert!(a >= b);
	}

	// -- Ord tests --

	/// Tests `Ord` for `Ok` values.
	#[test]
	fn test_try_lazy_ord_ok() {
		use std::cmp::Ordering;

		let a = RcTryLazy::<i32, ()>::ok(1);
		let b = RcTryLazy::<i32, ()>::ok(2);
		assert_eq!(a.cmp(&b), Ordering::Less);
		assert_eq!(b.cmp(&a), Ordering::Greater);
	}

	/// Tests `Ord` for equal values.
	#[test]
	fn test_try_lazy_ord_eq() {
		use std::cmp::Ordering;

		let a = RcTryLazy::<i32, ()>::ok(42);
		let b = RcTryLazy::<i32, ()>::ok(42);
		assert_eq!(a.cmp(&b), Ordering::Equal);
	}

	/// Tests `Ord` for `ArcTryLazy`.
	#[test]
	fn test_try_lazy_ord_arc() {
		use std::cmp::Ordering;

		let a = ArcTryLazy::<i32, ()>::ok(1);
		let b = ArcTryLazy::<i32, ()>::ok(2);
		assert_eq!(a.cmp(&b), Ordering::Less);
	}

	/// Tests `Eq` is implemented (compile-time check via trait bound).
	#[test]
	fn test_try_lazy_eq_trait() {
		fn assert_eq_impl<T: Eq>(_: &T) {}
		let a = RcTryLazy::<i32, ()>::ok(42);
		assert_eq_impl(&a);
	}

	// -- Display tests --

	/// Tests `Display` for `RcTryLazy` with `Ok` value.
	#[test]
	fn test_try_lazy_display_ok_rc() {
		let lazy = RcTryLazy::<i32, String>::ok(42);
		assert_eq!(format!("{}", lazy), "Ok(42)");
	}

	/// Tests `Display` for `RcTryLazy` with `Err` value.
	#[test]
	fn test_try_lazy_display_err_rc() {
		let lazy = RcTryLazy::<i32, String>::err("oops".to_string());
		assert_eq!(format!("{}", lazy), "Err(oops)");
	}

	/// Tests `Display` for `ArcTryLazy` with `Ok` value.
	#[test]
	fn test_try_lazy_display_ok_arc() {
		let lazy = ArcTryLazy::<i32, String>::ok(42);
		assert_eq!(format!("{}", lazy), "Ok(42)");
	}

	/// Tests `Display` for `ArcTryLazy` with `Err` value.
	#[test]
	fn test_try_lazy_display_err_arc() {
		let lazy = ArcTryLazy::<i32, String>::err("oops".to_string());
		assert_eq!(format!("{}", lazy), "Err(oops)");
	}

	// -- Cross-config conversion tests --

	/// Tests converting `RcTryLazy` to `ArcTryLazy` with `Ok` value.
	#[test]
	fn test_try_lazy_rc_to_arc_ok() {
		let rc_lazy = RcTryLazy::<i32, String>::ok(42);
		let arc_lazy: ArcTryLazy<i32, String> = ArcTryLazy::from(rc_lazy);
		assert_eq!(arc_lazy.evaluate(), Ok(&42));
	}

	/// Tests converting `RcTryLazy` to `ArcTryLazy` with `Err` value.
	#[test]
	fn test_try_lazy_rc_to_arc_err() {
		let rc_lazy = RcTryLazy::<i32, String>::err("fail".to_string());
		let arc_lazy: ArcTryLazy<i32, String> = ArcTryLazy::from(rc_lazy);
		assert_eq!(arc_lazy.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests converting `ArcTryLazy` to `RcTryLazy` with `Ok` value.
	#[test]
	fn test_try_lazy_arc_to_rc_ok() {
		let arc_lazy = ArcTryLazy::<i32, String>::ok(42);
		let rc_lazy: RcTryLazy<i32, String> = RcTryLazy::from(arc_lazy);
		assert_eq!(rc_lazy.evaluate(), Ok(&42));
	}

	/// Tests converting `ArcTryLazy` to `RcTryLazy` with `Err` value.
	#[test]
	fn test_try_lazy_arc_to_rc_err() {
		let arc_lazy = ArcTryLazy::<i32, String>::err("fail".to_string());
		let rc_lazy: RcTryLazy<i32, String> = RcTryLazy::from(arc_lazy);
		assert_eq!(rc_lazy.evaluate(), Err(&"fail".to_string()));
	}

	// -- rc_try_lazy_fix / arc_try_lazy_fix tests --

	/// Tests that `rc_try_lazy_fix` produces the correct `Ok` value when
	/// the function ignores the self-reference.
	#[test]
	fn test_rc_try_lazy_fix_ok_constant() {
		let fixed = rc_try_lazy_fix(|_self_ref: RcTryLazy<i32, ()>| Ok(42));
		assert_eq!(fixed.evaluate(), Ok(&42));
	}

	/// Tests that `rc_try_lazy_fix` produces the correct `Err` value when
	/// the function ignores the self-reference.
	#[test]
	fn test_rc_try_lazy_fix_err_constant() {
		let fixed = rc_try_lazy_fix(|_self_ref: RcTryLazy<i32, String>| Err("fail".to_string()));
		assert_eq!(fixed.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests that `rc_try_lazy_fix` memoizes the result.
	#[test]
	fn test_rc_try_lazy_fix_memoization() {
		let counter = Rc::new(RefCell::new(0));
		let counter_clone = counter.clone();
		let fixed = rc_try_lazy_fix(move |_self_ref: RcTryLazy<i32, ()>| {
			*counter_clone.borrow_mut() += 1;
			Ok(100)
		});

		assert_eq!(*counter.borrow(), 0);
		assert_eq!(fixed.evaluate(), Ok(&100));
		assert_eq!(*counter.borrow(), 1);
		// Second evaluation should use cached value.
		assert_eq!(fixed.evaluate(), Ok(&100));
		assert_eq!(*counter.borrow(), 1);
	}

	/// Tests that `rc_try_lazy_fix` correctly threads the self-reference.
	#[test]
	fn test_rc_try_lazy_fix_self_reference() {
		let fixed = rc_try_lazy_fix(|self_ref: RcTryLazy<Vec<i32>, ()>| {
			// The self-reference is available but evaluating it here would recurse.
			let _ = self_ref;
			Ok(vec![1, 2, 3])
		});
		assert_eq!(fixed.evaluate(), Ok(&vec![1, 2, 3]));
	}

	/// Tests that `rc_try_lazy_fix` works with cloned results sharing the cache.
	#[test]
	fn test_rc_try_lazy_fix_clone_sharing() {
		let fixed = rc_try_lazy_fix(|_self_ref: RcTryLazy<i32, ()>| Ok(55));
		let cloned = fixed.clone();
		assert_eq!(fixed.evaluate(), Ok(&55));
		assert_eq!(cloned.evaluate(), Ok(&55));
	}

	/// Tests that `rc_try_lazy_fix` uses the self-reference after initial evaluation.
	#[test]
	fn test_rc_try_lazy_fix_uses_self_ref() {
		let counter = Rc::new(RefCell::new(0));
		let counter_clone = counter.clone();
		let lazy = rc_try_lazy_fix(move |self_ref: RcTryLazy<i32, ()>| {
			*counter_clone.borrow_mut() += 1;
			let _ = self_ref;
			Ok(42)
		});
		assert_eq!(lazy.evaluate(), Ok(&42));
		assert_eq!(*counter.borrow(), 1);
		// Verify memoization: second evaluate does not re-run.
		assert_eq!(lazy.evaluate(), Ok(&42));
		assert_eq!(*counter.borrow(), 1);
	}

	/// Tests that `arc_try_lazy_fix` produces the correct `Ok` value when
	/// the function ignores the self-reference.
	#[test]
	fn test_arc_try_lazy_fix_ok_constant() {
		let fixed = arc_try_lazy_fix(|_self_ref: ArcTryLazy<i32, ()>| Ok(42));
		assert_eq!(fixed.evaluate(), Ok(&42));
	}

	/// Tests that `arc_try_lazy_fix` produces the correct `Err` value when
	/// the function ignores the self-reference.
	#[test]
	fn test_arc_try_lazy_fix_err_constant() {
		let fixed = arc_try_lazy_fix(|_self_ref: ArcTryLazy<i32, String>| Err("fail".to_string()));
		assert_eq!(fixed.evaluate(), Err(&"fail".to_string()));
	}

	/// Tests that `arc_try_lazy_fix` memoizes the result.
	#[test]
	fn test_arc_try_lazy_fix_memoization() {
		use std::sync::atomic::{
			AtomicUsize,
			Ordering,
		};

		let counter = Arc::new(AtomicUsize::new(0));
		let counter_clone = counter.clone();
		let fixed = arc_try_lazy_fix(move |_self_ref: ArcTryLazy<i32, ()>| {
			counter_clone.fetch_add(1, Ordering::SeqCst);
			Ok(100)
		});

		assert_eq!(counter.load(Ordering::SeqCst), 0);
		assert_eq!(fixed.evaluate(), Ok(&100));
		assert_eq!(counter.load(Ordering::SeqCst), 1);
		// Second evaluation should use cached value.
		assert_eq!(fixed.evaluate(), Ok(&100));
		assert_eq!(counter.load(Ordering::SeqCst), 1);
	}

	/// Tests that `arc_try_lazy_fix` correctly threads the self-reference.
	#[test]
	fn test_arc_try_lazy_fix_self_reference() {
		let fixed = arc_try_lazy_fix(|self_ref: ArcTryLazy<Vec<i32>, ()>| {
			let _ = self_ref;
			Ok(vec![1, 2, 3])
		});
		assert_eq!(fixed.evaluate(), Ok(&vec![1, 2, 3]));
	}

	/// Tests that `arc_try_lazy_fix` uses the self-reference after initial evaluation.
	#[test]
	fn test_arc_try_lazy_fix_uses_self_ref() {
		use std::sync::atomic::{
			AtomicUsize,
			Ordering,
		};

		let counter = Arc::new(AtomicUsize::new(0));
		let counter_clone = counter.clone();
		let lazy = arc_try_lazy_fix(move |self_ref: ArcTryLazy<i32, ()>| {
			counter_clone.fetch_add(1, Ordering::SeqCst);
			let _ = self_ref;
			Ok(42)
		});
		assert_eq!(lazy.evaluate(), Ok(&42));
		assert_eq!(counter.load(Ordering::SeqCst), 1);
		// Verify memoization: second evaluate does not re-run.
		assert_eq!(lazy.evaluate(), Ok(&42));
		assert_eq!(counter.load(Ordering::SeqCst), 1);
	}

	/// Tests that `arc_try_lazy_fix` is thread-safe.
	#[test]
	fn test_arc_try_lazy_fix_thread_safety() {
		use std::thread;

		let lazy = arc_try_lazy_fix(|self_ref: ArcTryLazy<i32, ()>| {
			let _ = self_ref;
			Ok(42)
		});

		let mut handles = vec![];
		for _ in 0 .. 10 {
			let lazy_clone = lazy.clone();
			handles.push(thread::spawn(move || {
				assert_eq!(lazy_clone.evaluate(), Ok(&42));
			}));
		}

		for handle in handles {
			handle.join().unwrap();
		}
	}

	// -- Knot-tying tests: self-reference is actually used after initialization --

	/// Tests that `rc_try_lazy_fix` ties the knot: the self-reference captured
	/// inside the closure points to the same `Rc` cell as the returned lazy.
	/// After evaluation, querying the self-reference yields the cached `Ok` value.
	#[test]
	fn test_rc_try_lazy_fix_knot_tying_ptr_eq() {
		let stash: Rc<RefCell<Option<RcTryLazy<i32, ()>>>> = Rc::new(RefCell::new(None));
		let stash_clone = stash.clone();
		let lazy = rc_try_lazy_fix(move |self_ref: RcTryLazy<i32, ()>| {
			*stash_clone.borrow_mut() = Some(self_ref);
			Ok(42)
		});
		assert_eq!(lazy.evaluate(), Ok(&42));
		let self_ref = stash.borrow().clone().unwrap();
		// The self-reference must point to the same underlying Rc cell.
		assert!(Rc::ptr_eq(&lazy.0.0, &self_ref.0.0));
		// Evaluating the self-reference yields the same cached value.
		assert_eq!(self_ref.evaluate(), Ok(&42));
	}

	/// Tests that `rc_try_lazy_fix` knot-tying produces a shared cache: the
	/// initializer runs exactly once even when accessed through the self-reference.
	#[test]
	fn test_rc_try_lazy_fix_knot_tying_shared_cache() {
		let counter = Rc::new(RefCell::new(0));
		let stash: Rc<RefCell<Option<RcTryLazy<i32, ()>>>> = Rc::new(RefCell::new(None));
		let counter_clone = counter.clone();
		let stash_clone = stash.clone();
		let lazy = rc_try_lazy_fix(move |self_ref: RcTryLazy<i32, ()>| {
			*stash_clone.borrow_mut() = Some(self_ref);
			*counter_clone.borrow_mut() += 1;
			Ok(100)
		});
		assert_eq!(*counter.borrow(), 0);
		assert_eq!(lazy.evaluate(), Ok(&100));
		assert_eq!(*counter.borrow(), 1);
		// Access through the stashed self-reference.
		let self_ref = stash.borrow().clone().unwrap();
		assert_eq!(self_ref.evaluate(), Ok(&100));
		// Counter must still be 1: the initializer was not re-run.
		assert_eq!(*counter.borrow(), 1);
	}

	/// Tests that `rc_try_lazy_fix` knot-tying works with `Err` results: the
	/// self-reference shares the cached error.
	#[test]
	fn test_rc_try_lazy_fix_knot_tying_err_shared() {
		let stash: Rc<RefCell<Option<RcTryLazy<i32, String>>>> = Rc::new(RefCell::new(None));
		let stash_clone = stash.clone();
		let lazy = rc_try_lazy_fix(move |self_ref: RcTryLazy<i32, String>| {
			*stash_clone.borrow_mut() = Some(self_ref);
			Err("fail".to_string())
		});
		assert_eq!(lazy.evaluate(), Err(&"fail".to_string()));
		let self_ref = stash.borrow().clone().unwrap();
		// The self-reference also sees the cached error.
		assert_eq!(self_ref.evaluate(), Err(&"fail".to_string()));
		// Both point to the same Rc cell.
		assert!(Rc::ptr_eq(&lazy.0.0, &self_ref.0.0));
	}

	/// Tests that `rc_try_lazy_fix` panics on reentrant evaluation.
	///
	/// Forcing the self-reference inside the initializer triggers a
	/// `LazyCell` reentrant-init panic.
	#[test]
	#[should_panic]
	fn test_rc_try_lazy_fix_reentrant_panics() {
		let lazy = rc_try_lazy_fix(|self_ref: RcTryLazy<i32, ()>| {
			// Forcing the self-reference during initialization is reentrant
			// and must panic.
			Ok(*self_ref.evaluate().unwrap() + 1)
		});
		let _ = lazy.evaluate();
	}

	/// Tests that `arc_try_lazy_fix` ties the knot: the self-reference captured
	/// inside the closure points to the same `Arc` cell as the returned lazy.
	#[test]
	fn test_arc_try_lazy_fix_knot_tying_ptr_eq() {
		use std::sync::Mutex;

		let stash: Arc<Mutex<Option<ArcTryLazy<i32, ()>>>> = Arc::new(Mutex::new(None));
		let stash_clone = stash.clone();
		let lazy = arc_try_lazy_fix(move |self_ref: ArcTryLazy<i32, ()>| {
			*stash_clone.lock().unwrap() = Some(self_ref);
			Ok(42)
		});
		assert_eq!(lazy.evaluate(), Ok(&42));
		let self_ref = stash.lock().unwrap().clone().unwrap();
		assert!(Arc::ptr_eq(&lazy.0.0, &self_ref.0.0));
		assert_eq!(self_ref.evaluate(), Ok(&42));
	}

	/// Tests that `arc_try_lazy_fix` knot-tying produces a shared cache: the
	/// initializer runs exactly once even when accessed through the self-reference.
	#[test]
	fn test_arc_try_lazy_fix_knot_tying_shared_cache() {
		use std::sync::{
			Mutex,
			atomic::{
				AtomicUsize,
				Ordering,
			},
		};

		let counter = Arc::new(AtomicUsize::new(0));
		let stash: Arc<Mutex<Option<ArcTryLazy<i32, ()>>>> = Arc::new(Mutex::new(None));
		let counter_clone = counter.clone();
		let stash_clone = stash.clone();
		let lazy = arc_try_lazy_fix(move |self_ref: ArcTryLazy<i32, ()>| {
			*stash_clone.lock().unwrap() = Some(self_ref);
			counter_clone.fetch_add(1, Ordering::SeqCst);
			Ok(100)
		});
		assert_eq!(counter.load(Ordering::SeqCst), 0);
		assert_eq!(lazy.evaluate(), Ok(&100));
		assert_eq!(counter.load(Ordering::SeqCst), 1);
		let self_ref = stash.lock().unwrap().clone().unwrap();
		assert_eq!(self_ref.evaluate(), Ok(&100));
		assert_eq!(counter.load(Ordering::SeqCst), 1);
	}

	/// Tests that `arc_try_lazy_fix` knot-tying works across threads: the
	/// self-reference can be evaluated from a different thread and still
	/// returns the cached value.
	#[test]
	fn test_arc_try_lazy_fix_knot_tying_cross_thread() {
		use std::{
			sync::Mutex,
			thread,
		};

		let stash: Arc<Mutex<Option<ArcTryLazy<i32, ()>>>> = Arc::new(Mutex::new(None));
		let stash_clone = stash.clone();
		let lazy = arc_try_lazy_fix(move |self_ref: ArcTryLazy<i32, ()>| {
			*stash_clone.lock().unwrap() = Some(self_ref);
			Ok(77)
		});
		assert_eq!(lazy.evaluate(), Ok(&77));
		let self_ref = stash.lock().unwrap().clone().unwrap();
		let handle = thread::spawn(move || self_ref.evaluate_owned());
		assert_eq!(handle.join().unwrap(), Ok(77));
	}
}