From 829640804418ede6f1baa0aa0101899941a7212e Mon Sep 17 00:00:00 2001
From: d-plaindoux <d.plaindoux@free.fr>
Date: Sun, 17 Sep 2023 00:39:43 +0200
Subject: [PATCH] Generic join and specific bind + Reader - Bind - bind and
 Monad

---
 src/specs/bind.rs        |  9 ++++-----
 src/standard/either.rs   | 11 +++++++----
 src/standard/identity.rs |  7 +++++--
 src/standard/option.rs   |  9 ++++++---
 src/standard/reader.rs   | 27 ++++++++++++++++++++++++---
 src/standard/result.rs   |  9 ++++++---
 src/standard/vec.rs      |  4 ----
 7 files changed, 52 insertions(+), 24 deletions(-)

diff --git a/src/specs/bind.rs b/src/specs/bind.rs
index bd9f84f..f541eef 100644
--- a/src/specs/bind.rs
+++ b/src/specs/bind.rs
@@ -4,14 +4,13 @@ pub trait Bind<'a>: Applicative<'a>
 where
     Self: 'a,
 {
-    fn join<A>(mma: Self::T<Self::T<A>>) -> Self::T<A>;
+    fn join<A>(mma: Self::T<Self::T<A>>) -> Self::T<A> {
+        Self::bind(mma, |e| e)
+    }
 
     fn bind<A, B, BIND>(ma: Self::T<A>, mf: BIND) -> Self::T<B>
     where
-        BIND: Fn(A) -> Self::T<B> + 'a,
-    {
-        Self::join(Self::map(mf, ma))
-    }
+        BIND: Fn(A) -> Self::T<B> + 'a;
 }
 
 pub mod infix {
diff --git a/src/standard/either.rs b/src/standard/either.rs
index b1c39bb..20a4c6a 100644
--- a/src/standard/either.rs
+++ b/src/standard/either.rs
@@ -49,10 +49,13 @@ impl<'a, E> Applicative<'a> for EitherK<E> {
 }
 
 impl<'a, E: 'a> Bind<'a> for EitherK<E> {
-    fn join<A: 'a>(mma: Self::T<Self::T<A>>) -> Self::T<A> {
-        match mma {
-            Left(ma) => Left(ma),
-            Right(r) => r,
+    fn bind<A: 'a, B: 'a, BIND>(ma: Self::T<A>, f: BIND) -> Self::T<B>
+    where
+        BIND: Fn(A) -> Self::T<B> + 'a,
+    {
+        match ma {
+            Left(a) => Left(a),
+            Right(r) => f(r),
         }
     }
 }
diff --git a/src/standard/identity.rs b/src/standard/identity.rs
index c776bcc..bf0c93f 100644
--- a/src/standard/identity.rs
+++ b/src/standard/identity.rs
@@ -37,8 +37,11 @@ impl<'a> Applicative<'a> for IdentityK {
 }
 
 impl<'a> Bind<'a> for IdentityK {
-    fn join<A: 'a>(mma: Self::T<Self::T<A>>) -> Self::T<A> {
-        mma.value
+    fn bind<A: 'a, B: 'a, BIND>(ma: Self::T<A>, f: BIND) -> Self::T<B>
+    where
+        BIND: Fn(A) -> Self::T<B> + 'a,
+    {
+        f(ma.value)
     }
 }
 
diff --git a/src/standard/option.rs b/src/standard/option.rs
index ee184bb..73853cd 100644
--- a/src/standard/option.rs
+++ b/src/standard/option.rs
@@ -36,9 +36,12 @@ impl<'a> Applicative<'a> for OptionK {
 }
 
 impl<'a> Bind<'a> for OptionK {
-    fn join<A: 'a>(mma: Self::T<Self::T<A>>) -> Self::T<A> {
-        match mma {
-            Some(ma) => ma,
+    fn bind<A: 'a, B: 'a, BIND>(ma: Self::T<A>, f: BIND) -> Self::T<B>
+    where
+        BIND: Fn(A) -> Self::T<B> + 'a,
+    {
+        match ma {
+            Some(a) => f(a),
             None => None,
         }
     }
diff --git a/src/standard/reader.rs b/src/standard/reader.rs
index fe1a4cf..62f2928 100644
--- a/src/standard/reader.rs
+++ b/src/standard/reader.rs
@@ -2,6 +2,7 @@ use crate::core::hkp::HKP;
 use crate::specs::applicative::Applicative;
 use crate::specs::bind::Bind;
 use crate::specs::functor::Functor;
+use crate::specs::monad::Monad;
 use std::marker::PhantomData;
 
 pub struct Reader<'a, E, F: HKP<'a>, A: 'a>(Box<dyn FnOnce(E) -> F::T<A> + 'a>, PhantomData<F>);
@@ -23,9 +24,10 @@ impl<'e, E, F: Functor<'e> + 'e> Functor<'e> for ReaderK<'e, E, F> {
     }
 }
 
-impl<'e, E: Clone, F: Applicative<'e> + 'e> Applicative<'e> for ReaderK<'e, E, F> {
+impl<'e, E: Copy, F: Applicative<'e> + 'e> Applicative<'e> for ReaderK<'e, E, F> {
     fn pure<A: 'e>(a: A) -> Self::T<A> {
-        Reader(Box::new(|_| F::pure(a)), PhantomData)
+        let run = |_| F::pure(a);
+        Reader(Box::new(run), PhantomData)
     }
 
     fn apply<A, B, MAP>(mf: Self::T<MAP>, ma: Self::T<A>) -> Self::T<B>
@@ -35,7 +37,26 @@ impl<'e, E: Clone, F: Applicative<'e> + 'e> Applicative<'e> for ReaderK<'e, E, F
     {
         let Reader(vf, _) = mf;
         let Reader(va, _) = ma;
-        let run = |e: E| F::apply(vf(e.clone()), va(e));
+        let run = |e: E| F::apply(vf(e), va(e));
+        Reader(Box::new(run), PhantomData)
+    }
+}
+
+impl<'e, E: Copy, F: Bind<'e> + 'e> Bind<'e> for ReaderK<'e, E, F> {
+    fn bind<A, B, BIND>(ma: Self::T<A>, f: BIND) -> Self::T<B>
+    where
+        BIND: Fn(A) -> Self::T<B> + 'e,
+    {
+        let Reader(va, _) = ma;
+        let run = move |e1: E| {
+            F::bind(va(e1), move |e2: A| {
+                let Reader(v, _) = f(e2);
+                v(e1)
+            })
+        };
+
         Reader(Box::new(run), PhantomData)
     }
 }
+
+impl<'e, E: Copy, F: Bind<'e> + 'e> Monad<'e> for ReaderK<'e, E, F> {}
diff --git a/src/standard/result.rs b/src/standard/result.rs
index a6cc3e5..1013083 100644
--- a/src/standard/result.rs
+++ b/src/standard/result.rs
@@ -40,9 +40,12 @@ impl<'a, E> Applicative<'a> for ResultK<E> {
 }
 
 impl<'a, E: 'a> Bind<'a> for ResultK<E> {
-    fn join<A: 'a>(mma: Self::T<Self::T<A>>) -> Self::T<A> {
-        match mma {
-            Ok(ma) => ma,
+    fn bind<A: 'a, B: 'a, BIND>(ma: Self::T<A>, f: BIND) -> Self::T<B>
+    where
+        BIND: Fn(A) -> Self::T<B> + 'a,
+    {
+        match ma {
+            Ok(a) => f(a),
             Err(e) => Err(e),
         }
     }
diff --git a/src/standard/vec.rs b/src/standard/vec.rs
index c5593a8..0c679cb 100644
--- a/src/standard/vec.rs
+++ b/src/standard/vec.rs
@@ -35,10 +35,6 @@ impl<'a> Applicative<'a> for VecK {
 }
 
 impl<'a> Bind<'a> for VecK {
-    fn join<A: 'a>(mma: Self::T<Self::T<A>>) -> Self::T<A> {
-        mma.into_iter().flatten().collect()
-    }
-
     fn bind<A: 'a, B: 'a, BIND>(ma: Self::T<A>, mf: BIND) -> Self::T<B>
     where
         BIND: Fn(A) -> Self::T<B> + 'a,