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use alloc::{vec, vec::Vec};
use core::marker::PhantomData;
pub trait Functor<T> {
type Type<A>;
fn fmap<U>(value: Self::Type<T>, f: impl FnMut(T) -> U) -> Self::Type<U>;
}
pub trait Applicative<T>: Functor<T> {
fn pure(inner: T) -> Self::Type<T>;
fn apply<U>(value: Self::Type<T>, f: Self::Type<impl FnMut(T) -> U>) -> Self::Type<U>;
}
pub trait Monad<T>: Applicative<T> {
fn bind<U>(value: Self::Type<T>, f: impl FnMut(T) -> Self::Type<U>) -> Self::Type<U>;
}
pub struct Maybe;
impl<T> Functor<T> for Maybe {
type Type<A> = Option<A>;
/// # Examples
///
/// ```
/// use std::ops::Not;
/// use ext::{assert_eqs, no_std::functions::{fun::s, fam::*}};
///
/// assert_eqs! {
/// Some(1), Maybe::fmap(0.into(), |x| x + 1);
/// Some(true), Maybe::fmap(false.into(), |x| x.not());
/// Some(s("abcd")), Maybe::fmap(s("ab").into(), |x| x + "cd");
/// }
/// ```
fn fmap<U>(value: Self::Type<T>, f: impl FnMut(T) -> U) -> Self::Type<U> {
value.map(f)
}
}
impl<T> Applicative<T> for Maybe {
/// # Examples
///
/// ```
/// use ext::{assert_eqs, no_std::functions::fam::*};
///
/// assert_eqs! {
/// Some(0), Maybe::pure(0);
/// Some(true), Maybe::pure(true);
/// Some("xy"), Maybe::pure("xy");
/// }
/// ```
fn pure(inner: T) -> Self::Type<T> {
inner.into()
}
/// # Examples
///
/// ```
/// use std::ops::Not;
/// use ext::{assert_eqs, no_std::functions::{fun::s, fam::*}};
///
/// assert_eqs! {
/// Some(1), Maybe::apply(0.into(), Some(|x| x + 1));
/// Some(true), Maybe::apply(false.into(), Some(|x: bool| x.not()));
/// Some(s("abcd")), Maybe::apply(s("ab").into(), Some(|x| x + "cd"));
/// }
/// ```
fn apply<U>(value: Self::Type<T>, f: Self::Type<impl FnMut(T) -> U>) -> Self::Type<U> {
value.zip(f).map(|(v, mut f)| f(v))
}
}
impl<T> Monad<T> for Maybe {
/// # Examples
///
/// ```
/// use std::ops::Not;
/// use ext::{assert_eqs, no_std::functions::{fun::s, fam::*}};
///
/// assert_eqs! {
/// Some(1), Maybe::bind(0.into(), |x| Some(x + 1));
/// Some(true), Maybe::bind(false.into(), |x| x.not().into());
/// Some(s("abcd")), Maybe::bind(s("ab").into(), |x| Some(x + "cd"));
/// }
/// ```
fn bind<U>(value: Self::Type<T>, f: impl FnMut(T) -> Self::Type<U>) -> Self::Type<U> {
value.and_then(f)
}
}
pub struct Either<E>(PhantomData<E>);
impl<T, E> Functor<T> for Either<E> {
type Type<A> = Result<A, E>;
/// # Examples
///
/// ```
/// use std::ops::Not;
/// use ext::{assert_eqs, no_std::functions::{fun::s, fam::*}};
///
/// assert_eqs! {
/// Ok::<_, ()>(1), Either::fmap(Ok(0), |x| x + 1);
/// Ok::<_, ()>(true), Either::fmap(Ok(false), |x| x.not());
/// Ok::<_, ()>(s("abcd")), Either::fmap(Ok(s("ab")), |x| x + "cd");
/// }
/// ```
fn fmap<U>(value: Self::Type<T>, f: impl FnMut(T) -> U) -> Self::Type<U> {
value.map(f)
}
}
impl<T, E> Applicative<T> for Either<E> {
/// # Examples
///
/// ```
/// use ext::{assert_eqs, no_std::functions::fam::*};
///
/// assert_eqs! {
/// Ok::<_, ()>(0), Either::pure(0);
/// Ok::<_, ()>(true), Either::pure(true);
/// Ok::<_, ()>("xy"), Either::pure("xy");
/// }
/// ```
fn pure(inner: T) -> Self::Type<T> {
Result::from(Ok(inner))
}
/// # Examples
///
/// ```
/// use std::ops::Not;
/// use ext::{assert_eqs, no_std::functions::{fun::s, fam::*}};
///
/// let mut f = Ok(|x| x + "cd");
/// f = Err(());
///
/// assert_eqs! {
/// Ok::<_, ()>(0), Either::apply(Ok(0), Ok(|x| x / 1));
/// Err(-1), Either::apply(Err(-1), Ok(|x: bool| x.not()));
/// Err(()), Either::apply(Ok(s("ab")), f);
/// }
/// ```
fn apply<U>(value: Self::Type<T>, f: Self::Type<impl FnMut(T) -> U>) -> Self::Type<U> {
use super::ext::ResultExt;
value.zip(f).map(|(v, mut f)| f(v))
}
}
impl<T, E> Monad<T> for Either<E> {
/// # Examples
///
/// ```
/// use std::ops::Not;
/// use ext::{assert_eqs, no_std::functions::{fun::s, fam::*}};
///
/// assert_eqs! {
/// Ok::<_, ()>(1), Either::bind(Ok(0), |x| Ok(x + 1));
/// Ok::<_, ()>(true), Either::bind(Ok(false), |x| Ok(x.not()));
/// Ok::<_, ()>(s("abcd")), Either::bind(Ok(s("ab")), |x| Ok(x + "cd"));
/// }
/// ```
fn bind<U>(value: Self::Type<T>, f: impl FnMut(T) -> Self::Type<U>) -> Self::Type<U> {
value.and_then(f)
}
}
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub struct Id<T>(pub T);
impl<T> Functor<T> for Id<T> {
type Type<A> = Id<A>;
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// let id = Id(23);
/// let res = Id::fmap(id, |x| x - 20);
/// assert_eq!(Id(3), res);
/// ```
fn fmap<U>(value: Self::Type<T>, mut f: impl FnMut(T) -> U) -> Self::Type<U> {
Id(f(value.0))
}
}
impl<T> Applicative<T> for Id<T> {
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// assert_eq!(Id(0), Id::pure(0));
/// ```
fn pure(inner: T) -> Self::Type<T> {
Id(inner)
}
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// let id = Id(23);
/// let res = Id::apply(id, Id(|x| x - 20));
/// assert_eq!(Id(3), res);
/// ```
fn apply<U>(value: Self::Type<T>, mut f: Self::Type<impl FnMut(T) -> U>) -> Self::Type<U> {
Id(f.0(value.0))
}
}
impl<T> Monad<T> for Id<T> {
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// let id = Id(23);
/// let res = Id::bind(id, |x| Id(x - 20));
/// assert_eq!(Id(3), res);
/// ```
fn bind<U>(value: Self::Type<T>, mut f: impl FnMut(T) -> Self::Type<U>) -> Self::Type<U> {
f(value.0)
}
}
pub struct Vector;
impl<T> Functor<T> for Vector {
type Type<A> = Vec<A>;
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// assert_eq!(vec![2, 4, 6], Vector::fmap(vec![1, 3, 5], |x| x + 1));
/// ```
fn fmap<U>(value: Self::Type<T>, f: impl FnMut(T) -> U) -> Self::Type<U> {
value.into_iter().map(f).collect()
}
}
impl<T> Applicative<T> for Vector {
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// assert_eq!(vec![0], Vector::pure(0));
/// ```
fn pure(inner: T) -> Self::Type<T> {
vec![inner]
}
/// # Examples
///
/// ```
/// use ext::no_std::functions::fam::*;
///
/// let add_one = |x| x + 1;
/// let mul_two = |y| y * 2;
/// assert_eq!(vec![3, 4], Vector::apply(vec![2, 2], Vec::from([add_one, mul_two])));
/// ```
fn apply<U>(value: Self::Type<T>, f: Self::Type<impl FnMut(T) -> U>) -> Self::Type<U> {
value
.into_iter()
.zip(f.into_iter())
.map(|(x, mut f)| f(x))
.collect()
}
}