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pub mod kind {
// Renamed from hkt to kind
//! # Kind-based Monad and Bind for the `monadify` library
//!
//! This module defines the `Monad` and `Bind` traits for Kind-encoded types.
//!
//! - [`Bind`]: Provides the `bind` method (often called `flatMap` or `>>=`),
//! which allows sequencing operations that return a monadic value. It extends [`Apply`].
//! - [`Monad`]: Extends [`Applicative`] (and thus `Bind` via `Applicative`'s supertrait `Apply`)
//! and adds the `join` method, which flattens a nested monadic structure (e.g., `F::Of<F::Of<A>>` to `F::Of<A>`).
//! Alternatively, a monad can be defined by `pure` (from `Applicative`) and `bind`.
//!
//! ## Example
//!
//! ```
//! use monadify::monad::kind::{Monad, Bind};
//! use monadify::applicative::kind::Applicative; // For pure
//! use monadify::kind_based::kind::OptionKind;
//!
//! // Using bind
//! let opt_val: Option<i32> = Some(5);
//! let bind_fn = |x: i32| if x > 0 { Some(x * 2) } else { None };
//! let result_bind: Option<i32> = OptionKind::bind(opt_val, bind_fn);
//! assert_eq!(result_bind, Some(10));
//!
//! let opt_val_none: Option<i32> = Some(-5);
//! let result_bind_none: Option<i32> = OptionKind::bind(opt_val_none, bind_fn);
//! assert_eq!(result_bind_none, None);
//!
//! // Using join
//! let nested_opt: Option<Option<String>> = Some(Some("hello".to_string()));
//! let joined_opt: Option<String> = OptionKind::join(nested_opt);
//! assert_eq!(joined_opt, Some("hello".to_string()));
//!
//! let nested_none_inner: Option<Option<String>> = Some(None);
//! let joined_none_inner: Option<String> = OptionKind::join(nested_none_inner);
//! assert_eq!(joined_none_inner, None);
//!
//! let nested_none_outer: Option<Option<String>> = None;
//! let joined_none_outer: Option<String> = OptionKind::join(nested_none_outer);
//! assert_eq!(joined_none_outer, None);
//! ```
use crate::applicative::kind::Applicative; // Kind-based Applicative
use crate::apply::kind::Apply; // Kind-based Apply
use crate::function::{CFnOnce, RcFn};
use crate::kind_based::kind::{
CFnOnceKind, Kind, Kind1, OptionKind, RcFnKind, ResultKind, VecKind,
};
use std::rc::Rc;
/// Kind-based `Monad` trait.
///
/// A `Monad` allows for sequencing computations within a context. It extends
/// [`Applicative`]. The key additional operation is `join`, which flattens
/// nested monadic structures.
///
/// `Self` refers to the Kind marker type (e.g., [`OptionKind`]) that implements
/// [`Kind1`] and [`Applicative`].
/// `A` is the type of the value held within the monadic context (e.g., the `T` in `Option<T>`).
///
/// ## Monad Laws
/// Implementors must satisfy several laws:
/// 1. **Left Identity**: `bind(pure(x), f) == f(x)`
/// 2. **Right Identity**: `bind(m, pure) == m`
/// 3. **Associativity**: `bind(bind(m, f), g) == bind(m, |x| bind(f(x), g))`
///
/// These laws can also be expressed using `join`, `pure`, and `map` (from `Functor`,
/// which `Applicative` extends):
/// 1. `join(pure(m)) == m`
/// 2. `join(map(m, pure)) == m`
/// 3. `join(map(mma, join)) == join(join(mma))` (if `map` is defined for `F::Of<F::Of<F::Of<A>>>`)
/// or more commonly: `join(map(mmma, |mma| join(mma))) == join(join(mmma))`
pub trait Monad<A>: Applicative<A>
// Monad holds type A
where
Self: Sized + Kind1, // Self is the Kind Marker
A: 'static,
{
/// Flattens a nested monadic structure.
///
/// For a Kind `F`, `join` takes `F::Of<F::Of<A>>` and returns `F::Of<A>`.
///
/// # Example
/// ```
/// use monadify::monad::kind::Monad;
/// use monadify::kind_based::kind::OptionKind;
///
/// let nested: Option<Option<i32>> = Some(Some(10));
/// let flat: Option<i32> = OptionKind::join(nested);
/// assert_eq!(flat, Some(10));
///
/// let nested_none: Option<Option<i32>> = Some(None);
/// assert_eq!(OptionKind::join(nested_none), None);
/// ```
#[must_use]
fn join(mma: Self::Of<Self::Of<A>>) -> Self::Of<A>; // Changed Applied to Of
}
/// Kind-based `Bind` trait (equivalent to `flatMap` or Haskell's `>>=`).
///
/// `Bind` allows sequencing operations where each operation takes a normal value
/// and returns a value wrapped in the Kind context. It extends [`Apply`].
///
/// `Self` refers to the Kind marker type (e.g., [`OptionKind`]).
/// `A` is the type of the value within the input Kind context `Self::Of<A>`.
/// `B` is the type of the value within the output Kind context `Self::Of<B>`
/// that the provided function `func` returns.
///
/// ## Example
/// ```
/// use monadify::monad::kind::Bind;
/// use monadify::kind_based::kind::OptionKind;
///
/// let opt_val: Option<i32> = Some(5);
///
/// // Function that returns an Option
/// let half = |x: i32| -> Option<f64> {
/// if x % 2 == 0 { Some((x as f64) / 2.0) } else { None }
/// };
///
/// let result: Option<f64> = OptionKind::bind(opt_val, half); // Fails as 5 is odd
/// assert_eq!(result, None);
///
/// let result_even: Option<f64> = OptionKind::bind(Some(10), half); // Succeeds
/// assert_eq!(result_even, Some(5.0));
/// ```
pub trait Bind<A, B>: Apply<A, B>
where
Self: Sized + Kind1, // Changed HKT1 to Kind1
A: 'static,
B: 'static,
{
/// Sequentially composes computations within the Kind context.
///
/// Takes a value in context (`Self::Of<A>`) and a function (`A -> Self::Of<B>`).
/// It applies the function to the unwrapped value (if present/valid) and returns
/// the resulting context `Self::Of<B>`.
#[must_use]
fn bind(
input: Self::Of<A>,
func: impl FnMut(A) -> Self::Of<B> + Clone + 'static,
) -> Self::Of<B>; // Changed Applied to Of
}
// --- Bind Implementations ---
impl<A: 'static, B: 'static> Bind<A, B> for OptionKind {
// Changed OptionHKTMarker to OptionKind
/// For `Option`, `bind` is equivalent to `Option::and_then`.
/// If `input` is `Some(a)`, it applies `func` to `a`.
/// If `input` is `None`, it returns `None`.
fn bind(
input: Self::Of<A>,
func: impl FnMut(A) -> Self::Of<B> + Clone + 'static,
) -> Self::Of<B> {
// Changed Applied to Of
input.and_then(func)
}
}
impl<A: 'static, B: 'static, E: 'static + Clone> Bind<A, B> for ResultKind<E> {
// Changed ResultHKTMarker to ResultKind
/// For `Result`, `bind` is equivalent to `Result::and_then`.
/// If `input` is `Ok(a)`, it applies `func` to `a`.
/// If `input` is `Err(e)`, it propagates the `Err(e)`.
fn bind(
input: Self::Of<A>,
func: impl FnMut(A) -> Self::Of<B> + Clone + 'static,
) -> Self::Of<B> {
// Changed Applied to Of
input.and_then(func)
}
}
impl<A: 'static + Clone, B: 'static> Bind<A, B> for VecKind {
// Changed VecHKTMarker to VecKind
/// For `Vec`, `bind` applies `func` to each element and flattens the results.
/// This is equivalent to `Vec::into_iter().flat_map(func).collect()`.
fn bind(
input: Self::Of<A>,
func: impl FnMut(A) -> Self::Of<B> + Clone + 'static,
) -> Self::Of<B> {
// Changed Applied to Of
input.into_iter().flat_map(func).collect()
}
}
// Bind for RcFnKind<R> (Kleisli composition for R -> _)
// input: RcFn<R, A>; func: A -> RcFn<R, B>; result: RcFn<R, B>
impl<R, A, B: 'static> Bind<A, B> for RcFnKind<R>
where
R: 'static + Clone,
A: 'static,
Self: Apply<A, B>,
Self: Kind<Of<A> = RcFn<R, A>>,
Self: Kind<Of<B> = RcFn<R, B>>,
{
/// Implements Kleisli composition for `RcFn<R, A>` and `A -> RcFn<R, B>`.
///
/// The resulting `RcFn<R, B>`, when called with `r: R`:
/// 1. Calls `input(r.clone())` to get `a: A`.
/// 2. Calls `func(a)` to get `rcfn_r_b: RcFn<R, B>`.
/// 3. Calls `rcfn_r_b(r)` to get `b: B`.
fn bind(
input: Self::Of<A>,
func: impl FnMut(A) -> Self::Of<B> + Clone + 'static,
) -> Self::Of<B> {
let inner = input.0.clone();
RcFn(Rc::new(move |r: R| {
let a_val = inner(r.clone());
let mut func_clone = func.clone();
let rcfn_r_b: RcFn<R, B> = func_clone(a_val);
rcfn_r_b.call(r)
}))
}
}
impl<R, A, B: 'static> Bind<A, B> for CFnOnceKind<R>
// Changed CFnOnceHKTMarker to CFnOnceKind
where
R: 'static + Clone,
A: 'static,
Self: Apply<A, B>,
Self: Kind<Of<A> = CFnOnce<R, A>>, // Changed HKT to Kind, Applied to Of
Self: Kind<Of<B> = CFnOnce<R, B>>, // Changed HKT to Kind, Applied to Of
{
/// Implements Kleisli composition for functions `R -> A` (once) and `A -> (R -> B)` (once).
///
/// Implements Kleisli composition for `CFnOnce`: analogous to `RcFnKind::bind` but for single-use closures.
/// The resulting function `R -> B` can also only be called once.
fn bind(
input: Self::Of<A>,
mut func: impl FnMut(A) -> Self::Of<B> + Clone + 'static,
) -> Self::Of<B> {
// Changed Applied to Of
let concrete_input = input; // CFnOnce<R,A>
CFnOnce::new(move |r: R| {
let a_val = concrete_input.call_once(r.clone());
let cfn_once_r_b = func(a_val); // CFnOnce<R,B>
cfn_once_r_b.call_once(r)
})
}
}
// --- Monad Implementations ---
impl<A: 'static> Monad<A> for OptionKind {
// Changed OptionHKTMarker to OptionKind
/// Flattens `Option<Option<A>>` to `Option<A>`.
/// `Some(Some(a))` becomes `Some(a)`.
/// `Some(None)` becomes `None`.
/// `None` becomes `None`.
fn join(mma: Self::Of<Self::Of<A>>) -> Self::Of<A> {
// mma is Option<Option<A>>. Changed Applied to Of
mma.flatten()
}
}
impl<A: 'static, E: 'static + Clone> Monad<A> for ResultKind<E> {
// Changed ResultHKTMarker to ResultKind
/// Flattens `Result<Result<A, E>, E>` to `Result<A, E>`.
/// `Ok(Ok(a))` becomes `Ok(a)`.
/// `Ok(Err(e))` becomes `Err(e)`.
/// `Err(e)` becomes `Err(e)`.
fn join(mma: Self::Of<Self::Of<A>>) -> Self::Of<A> {
// mma is Result<Result<A,E>, E>. Changed Applied to Of
mma.and_then(core::convert::identity)
}
}
impl<A: 'static + Clone> Monad<A> for VecKind {
// Changed VecHKTMarker to VecKind
/// Flattens `Vec<Vec<A>>` to `Vec<A>`.
/// `vec![vec![1, 2], vec![3]]` becomes `vec![1, 2, 3]`.
fn join(mma: Self::Of<Self::Of<A>>) -> Self::Of<A> {
// mma is Vec<Vec<A>>. Changed Applied to Of
mma.into_iter().flatten().collect()
}
}
impl<R, A> Monad<A> for RcFnKind<R>
where
R: 'static + Clone,
A: 'static + Clone, // required by Applicative<A> supertrait for RcFnKind<R>
{
/// Flattens `RcFn<R, RcFn<R, A>>` to `RcFn<R, A>`.
///
/// Implemented via `bind` with the identity function `|ma: RcFn<R,A>| ma`.
/// Because `RcFn` is `Clone`, the inner type `A = RcFn<R, A>` satisfies
/// the `Clone` constraint (unlike the old `Box`-backed approach which blocked this).
fn join(mma: Self::Of<Self::Of<A>>) -> Self::Of<A> {
<Self as Bind<Self::Of<A>, A>>::bind(mma, |ma: Self::Of<A>| ma)
}
}
impl<R, A> Monad<A> for CFnOnceKind<R>
// Changed CFnOnceHKTMarker to CFnOnceKind
where
R: 'static + Clone,
A: 'static + Clone, // From Applicative supertrait for CFnOnceKind<R>
{
/// Flattens `CFnOnce<R, CFnOnce<R, A>>` to `CFnOnce<R, A>`.
///
/// Analogous to `RcFnKind::join`, but for single-use `CFnOnce` closures.
fn join(mma: Self::Of<Self::Of<A>>) -> Self::Of<A> {
// mma is CFnOnce<R, CFnOnce<R,A>>. Changed Applied to Of
<Self as Bind<Self::Of<A>, A>>::bind(mma, |ma: Self::Of<A>| ma) // Changed Applied to Of
}
}
/// Helper function for `Bind::bind`.
///
/// This allows calling `bind(func, ma)` instead of `F::bind(ma, func)`.
///
/// # Example
/// ```
/// use monadify::monad::kind::bind; // The helper function
/// use monadify::kind_based::kind::OptionKind;
///
/// let opt_val: Option<i32> = Some(5);
/// let half = |x: i32| if x % 2 == 0 { Some((x as f64) / 2.0) } else { None };
///
/// // Note: Type of F (OptionKind) might need to be inferred or specified
/// let result: Option<f64> = bind::<OptionKind, _, _, _>(half, opt_val);
/// assert_eq!(result, None);
/// ```
#[must_use]
pub fn bind<F, A, B, FuncImpl>(
func: FuncImpl,
ma: F::Of<A>, // Changed Applied to Of
) -> F::Of<B>
// Changed Applied to Of
where
F: Bind<A, B> + Kind1, // F is the KindMarker. Changed HKT1 to Kind1
FuncImpl: FnMut(A) -> F::Of<B> + Clone + 'static, // Changed Applied to Of
A: 'static,
B: 'static, // B needs to be 'static for F::Of<B>
{
F::bind(ma, func)
}
}
// Directly export Kind-based Bind, Monad, and helper bind
pub use kind::{bind, Bind, Monad}; // Renamed from hkt to kind
// Note: join is a method on the Monad trait in the kind module.