From 629a0c9c83fffb60ef7cfe9de6079d22ab8771dc Mon Sep 17 00:00:00 2001
From: timofey <tim@ongoteam.yaconnect.com>
Date: Sun, 7 May 2023 18:21:57 +0000
Subject: [PATCH] `derivations::bind`

---
 src/func.rs             | 2 ++
 src/func/derivations.rs | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/src/func.rs b/src/func.rs
index 23c6385..9b09ec6 100644
--- a/src/func.rs
+++ b/src/func.rs
@@ -166,6 +166,8 @@ pub trait Applicative: Pure + ApplicativeSeq + ApplicativeLA2 + ApplicativeTuple
 /// <https://hackage.haskell.org/package/base-4.18.0.0/docs/Control-Monad.html>
 pub trait Monad: Applicative {
     /// Equivalent of Haskell's `>==`.
+    /// Due to Rust limitations, it's not a `function->function` conversion.
+    /// For that see [`derivations::bind`].
     fn bind<'a, A: 'a, B: 'a>(
         fa: Self::F<'a, A>,
         f: impl 'a + FnOnce(A) -> Self::F<'a, B>,
diff --git a/src/func/derivations.rs b/src/func/derivations.rs
index 37e6dce..9fd169d 100644
--- a/src/func/derivations.rs
+++ b/src/func/derivations.rs
@@ -9,6 +9,13 @@ pub fn fmap<'a, T: 'a + Functor, A: 'a, B: 'a>(
     move |fa| T::fmap(f, fa)
 }
 
+/// Equivalent of Haskell's `fmap`. `function-function` equivalent of [Monad::bind].
+pub fn bind<'a, T: 'a + Monad, A: 'a, B: 'a>(
+    f: impl 'a + FnOnce(A) -> T::F<'a, B>,
+) -> impl FnOnce(T::F<'a, A>) -> T::F<'a, B> {
+    move |fa| T::bind(fa, f)
+}
+
 pub trait ApplicativeLA2ViaSeq: ApplicativeSeq {
     fn _la2_via_seq<'a, A: 'a, B: 'a, C: 'a>(
         f: impl 'a + FnOnce(A, B) -> C,