higher-cat 0.1.1

Functors, Applicatives, Monads and other bad ideas
Documentation 
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use std::collections::{BTreeMap, HashMap};
use std::hash::{BuildHasher, Hash};

use higher::Bilift;

/// A `Bifunctor` lets you change the types of a generic type with two type
/// parameters.
///
/// A `Bifunctor` works just like a `Functor`, but for types with two type
/// parameters. It will convert a `F<_, _>: Bifunctor` from `F<A, B>` to
/// `F<C, D>` using two functions, one `Fn(A) -> C` and the other `Fn(B) -> D`.
pub trait Bifunctor<A, B, C, D>: Bilift<A, B, C, D> {
    fn bimap<L, R>(self, left: L, right: R) -> <Self as Bilift<A, B, C, D>>::Target
    where
        L: Fn(A) -> C,
        R: Fn(B) -> D;
}

pub trait BifunctorLeft<A, B, C>: Bifunctor<A, B, C, B> {
    fn lmap<F>(self, f: F) -> <Self as Bilift<A, B, C, B>>::Target
    where
        F: Fn(A) -> C;
}

impl<A, B, C> BifunctorLeft<A, B, C> for A
where
    A: Bifunctor<A, B, C, B>,
{
    fn lmap<F>(self, f: F) -> <Self as Bilift<A, B, C, B>>::Target
    where
        F: Fn(A) -> C,
    {
        self.bimap(f, |a| a)
    }
}

pub trait BifunctorRight<A, B, C>: Bifunctor<A, B, A, C> {
    fn rmap<F>(self, f: F) -> <Self as Bilift<A, B, A, C>>::Target
    where
        F: Fn(B) -> C;
}

impl<A, B, C> BifunctorRight<A, B, C> for A
where
    A: Bifunctor<A, B, A, C>,
{
    fn rmap<F>(self, f: F) -> <Self as Bilift<A, B, A, C>>::Target
    where
        F: Fn(B) -> C,
    {
        self.bimap(|a| a, f)
    }
}

impl<A, B, C, D> Bifunctor<A, B, C, D> for Result<A, B> {
    fn bimap<L, R>(self, left: L, right: R) -> <Self as Bilift<A, B, C, D>>::Target
    where
        L: Fn(A) -> C,
        R: Fn(B) -> D,
    {
        match self {
            Ok(a) => Ok(left(a)),
            Err(b) => Err(right(b)),
        }
    }
}

impl<A, B, C, D, S> Bifunctor<A, B, C, D> for HashMap<A, B, S>
where
    A: Eq + Hash,
    C: Eq + Hash,
    S: BuildHasher + Default,
{
    fn bimap<L, R>(self, left: L, right: R) -> <Self as Bilift<A, B, C, D>>::Target
    where
        L: Fn(A) -> C,
        R: Fn(B) -> D,
    {
        self.into_iter().map(|(k, v)| (left(k), right(v))).collect()
    }
}

impl<A, B, C, D> Bifunctor<A, B, C, D> for BTreeMap<A, B>
where
    A: Ord,
    C: Ord,
{
    fn bimap<L, R>(self, left: L, right: R) -> <Self as Bilift<A, B, C, D>>::Target
    where
        L: Fn(A) -> C,
        R: Fn(B) -> D,
    {
        self.into_iter().map(|(k, v)| (left(k), right(v))).collect()
    }
}