From f1cdbcc2d0da5296b37e22c51eb926c4c389a92c Mon Sep 17 00:00:00 2001
From: timofey <tim@ongoteam.yaconnect.com>
Date: Sat, 20 May 2023 06:02:51 +0000
Subject: [PATCH] `Fail`

---
 src/func.rs                     | 15 ++++++++++-----
 src/func/classes/composition.rs |  2 +-
 src/func/classes/option.rs      |  2 +-
 src/func/classes/result.rs      |  2 +-
 src/func/classes/solo.rs        |  2 +-
 src/func/classes/tryfuture.rs   |  2 +-
 6 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/func.rs b/src/func.rs
index 5c7d872..6d5d013 100644
--- a/src/func.rs
+++ b/src/func.rs
@@ -223,10 +223,8 @@ pub trait Monad: Applicative {
     }
 }
 
-/// Equivalent of Haskell's `MonadFail`.
-///
-/// <https://hackage.haskell.org/package/base-4.18.0.0/docs/Control-Monad.html>
-pub trait MonadFail<E>: Monad {
+/// Part of [`MonadFail`] responsible for Haskell's `fail`.
+pub trait Fail<E>: WeakFunctor {
     /// Equivalent of Haskell's `fail`.
     fn fail<'a, A: 'a>(e: E) -> Self::F<'a, A>
     where
@@ -234,6 +232,13 @@ pub trait MonadFail<E>: Monad {
         E: 'a;
 }
 
+/// Equivalent of Haskell's `MonadFail`. Auto-implemented for all [`Fail`]`+`[`Monad`].
+///
+/// <https://hackage.haskell.org/package/base-4.18.0.0/docs/Control-Monad.html>
+pub trait MonadFail<E>: Monad + Fail<E> {}
+
+impl<E, T: Monad + Fail<E>> MonadFail<E> for T {}
+
 /// Equivalent of Haskell's `Alternative`.
 /// Lacks `some`/`many` definitions due to [`FnOnce`] category semantics.
 ///
@@ -296,7 +301,7 @@ pub trait MonadFailAny {
     {
         <Self::W<Result<E1, E0>> as Monad>::bind(Self::map_err(wa, Err), |fa| match fa {
             Ok(a) => <Self::W<Result<E1, E0>> as Pure>::pure(a),
-            Err(e) => <Self::W<Result<E1, E0>> as MonadFail<Result<E1, E0>>>::fail(Ok(e)),
+            Err(e) => <Self::W<Result<E1, E0>> as Fail<Result<E1, E0>>>::fail(Ok(e)),
         })
     }
 }
diff --git a/src/func/classes/composition.rs b/src/func/classes/composition.rs
index b22a1b0..0e23c3f 100644
--- a/src/func/classes/composition.rs
+++ b/src/func/classes/composition.rs
@@ -189,7 +189,7 @@ impl<
     }
 }
 
-impl<E, U: Monad, V: MonadFail<E> + LocalFunctor> MonadFail<E> for CompositionClass<U, V> {
+impl<E, U: Monad, V: Fail<E> + LocalFunctor> Fail<E> for CompositionClass<U, V> {
     fn fail<'a, A: 'a>(e: E) -> Self::F<'a, A>
     where
         Self: 'a,
diff --git a/src/func/classes/option.rs b/src/func/classes/option.rs
index d598d33..758da1d 100644
--- a/src/func/classes/option.rs
+++ b/src/func/classes/option.rs
@@ -164,7 +164,7 @@ impl LocalFunctor for OptionClass {
     }
 }
 
-impl MonadFail<()> for OptionClass {
+impl Fail<()> for OptionClass {
     fn fail<'a, A: 'a>(_e: ()) -> Self::F<'a, A>
     where
         Self: 'a,
diff --git a/src/func/classes/result.rs b/src/func/classes/result.rs
index d778bcb..2869843 100644
--- a/src/func/classes/result.rs
+++ b/src/func/classes/result.rs
@@ -188,7 +188,7 @@ impl<E> LocalFunctor for ResultClass<E> {
     }
 }
 
-impl<E> MonadFail<E> for ResultClass<E> {
+impl<E> Fail<E> for ResultClass<E> {
     fn fail<'a, A: 'a>(e: E) -> Self::F<'a, A>
     where
         Self: 'a,
diff --git a/src/func/classes/solo.rs b/src/func/classes/solo.rs
index 4fb78fa..b631c2a 100644
--- a/src/func/classes/solo.rs
+++ b/src/func/classes/solo.rs
@@ -145,7 +145,7 @@ impl LocalFunctor for SoloClass {
     }
 }
 
-impl MonadFail<std::convert::Infallible> for SoloClass {
+impl Fail<std::convert::Infallible> for SoloClass {
     fn fail<'a, A: 'a>(e: std::convert::Infallible) -> Self::F<'a, A>
     where
         Self: 'a,
diff --git a/src/func/classes/tryfuture.rs b/src/func/classes/tryfuture.rs
index fb8cf97..b531dfb 100644
--- a/src/func/classes/tryfuture.rs
+++ b/src/func/classes/tryfuture.rs
@@ -182,7 +182,7 @@ impl<E: Clone> SharedFunctor for TryFutureClass<E> {
     }
 }
 
-impl<E> MonadFail<E> for TryFutureClass<E> {
+impl<E> Fail<E> for TryFutureClass<E> {
     fn fail<'a, A: 'a>(e: E) -> Self::F<'a, A>
     where
         Self: 'a,