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use crate::prelude::*;
/// [`Apply`], but specialized to know at compile-time
/// that the function contained in `F` will only be called one time.
pub trait ApplyOnce<F, AB>
where Self: Functor<F, AB>,
F: HKT1<T<AB> = Self>
{
/// See [`ApplyOnce`]
fn apply1<A, B>(self, a: F::T<A>) -> F::T<B>
where AB: F1Once<A, Ret = B>;
}
/// `Apply` generalizes [`Functor`] to any arity.
///
/// In other words, you can lift a function
///
/// `A -> B -> C -> D`
///
/// to
///
/// `F<A> -> F<B> -> F<C> -> F<D>`.
///
/// # Example
/// ```
/// use naan::prelude::*;
///
/// fn maybe_n() -> Option<usize> {
/// Some(1)
/// }
///
/// fn maybe_string() -> Option<String> {
/// None
/// }
///
/// fn maybe_bytes() -> Option<Vec<u8>> {
/// None
/// }
///
/// fn combine_many_things(n: usize, string: String, bytes: Vec<u8>) {
/// // ...
/// }
///
/// # fn a() {
/// Some(combine_many_things.curry()).apply(maybe_n())
/// .apply(maybe_string())
/// .apply(maybe_bytes());
///
/// // with `if let`:
/// if let Some(n) = maybe_n() {
/// if let Some(s) = maybe_string() {
/// if let Some(bs) = maybe_bytes() {
/// combine_many_things(n, s, bs);
/// }
/// }
/// }
///
/// // with `let else`:
/// let Some(n) = maybe_n() else {return};
/// let Some(s) = maybe_string() else {return};
/// let Some(bs) = maybe_bytes() else {return};
/// combine_many_things(n, s, bs);
///
/// // with `match`:
/// match (maybe_n(), maybe_string(), maybe_bytes()) {
/// | (Some(n), Some(s), Some(bs)) => combine_many_things(n, s, bs),
/// | _ => (),
/// }
/// # }
/// ```
pub trait Apply<F, AB>
where Self: Functor<F, AB>,
F: HKT1<T<AB> = Self>
{
/// See [`Apply.apply_with`]
fn apply<A, B>(self, a: F::T<A>) -> F::T<B>
where Self: Sized,
AB: F1<A, Ret = B>,
A: Clone
{
self.apply_with(a, Clone::clone)
}
/// Apply the function `A -> B` contained in `Self` (`F<A -> B>`) to
/// an instance of `F<A>` to get `F<B>`.
fn apply_with<A, B, Cloner>(self, a: F::T<A>, cloner: Cloner) -> F::T<B>
where AB: F1<A, Ret = B>,
Cloner: for<'a> F1<&'a A, Ret = A>;
}
/// Adds onto [`Apply`] the ability to lift a _value_
/// to the `F` context.
pub trait Applicative<F, A>
where Self: Apply<F, A>,
F: HKT1<T<A> = Self>
{
/// Lift `A` to `F<A>`
fn pure(a: A) -> F::T<A>;
/// Append a single `A` to `F<A>`
fn append_one(self, a: A) -> Self
where Self: Sized + Semigroup
{
self.append(Self::pure(a))
}
}
/// [`Apply`] but with looser type constraints,
/// allowing for blanket [`Apply`] implementations
/// on types [`Equiv`]alent to `F<AB>`
pub trait ApplySurrogate<F, AB, TofA>
where Self: FunctorSurrogate<F, AB> + Equiv<To = F::T<AB>>,
F: HKT1
{
/// Type returned by `apply_` that is
/// conceptually the same as `F::T<B>`.
///
/// Related: [`FunctorSurrogate::Output`]
type ApplyOutput<A, B>: Equiv<To = F::T<B>>;
/// Apply the function `A -> B` contained in `Self` (`F<A -> B>`) to
/// an instance of `F<A>` to get `F<B>`.
fn apply_<A, B>(self, a: TofA) -> Self::ApplyOutput<A, B>
where AB: F1Once<A, Ret = B>;
}
/// [`Applicative`] but with looser type constraints,
/// allowing for blanket [`Applicative`] implementations
/// on types [`Equiv`]alent to `F<A>`
pub trait ApplicativeSurrogate<F, A>
where Self: Sized + ApplySurrogate<F, A, Self> + Equiv<To = F::T<A>>,
F: HKT1
{
/// Lift `A` to `F<A>`
fn pure(a: A) -> F::T<A>;
}