From 5319f02fc40273c17875a605c40f9e900c1cedaf Mon Sep 17 00:00:00 2001
From: mauke <lukasmai.403@gmail.com>
Date: Tue, 4 Jul 2023 09:21:23 +0200
Subject: [PATCH] simplify the distribute Return case

This commit shouldn't change the meaning of the code:

    lift (Return r) =
     -- by Monad instance of Stream
    lift (return r) =
     -- by laws of MonadTrans/lift
    return r

However, the result may be more efficient. In the case where t = Stream f, we have:

    lift (Return r) =
     -- by definition of lift
    (Effect . fmap Return) (Return r) =
     -- by definition of (.)
    Effect (fmap Return (Return r)) =
     -- by definition of fmap
    Effect (Return (Return r))

But doing `return r` directly produces just `Return r` (without the no-op Effect wrapper).
---
 src/Streaming/Internal.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Streaming/Internal.hs b/src/Streaming/Internal.hs
index d62325c..53ae081 100644
--- a/src/Streaming/Internal.hs
+++ b/src/Streaming/Internal.hs
@@ -763,7 +763,7 @@ distribute :: (Monad m, Functor f, MonadTrans t, MFunctor t, Monad (t (Stream f
            => Stream f (t m) r -> t (Stream f m) r
 distribute = loop where
   loop stream = case stream of
-    Return r     -> lift (Return r)
+    Return r     -> return r
     Effect tmstr -> hoist lift tmstr >>= loop
     Step fstr    -> join (lift (Step (fmap (Return . loop) fstr)))
 {-# INLINABLE distribute #-}