From: Ross Paterson <ross@soi.city.ac.uk>
Date: Mon, 3 Jan 2011 18:57:22 +0000 (+0000)
Subject: Add Applicative instances for ST monads (proposal #4455)
X-Git-Url: http://git.megacz.com/?p=ghc-base.git;a=commitdiff_plain;h=6c5da11b55ef71607cf0b8cf408c10cd5f99530c

Add Applicative instances for ST monads (proposal #4455)

patch from Bas van Dijk
---

diff --git a/Control/Applicative.hs b/Control/Applicative.hs
index 154b591..ab6b365 100644
--- a/Control/Applicative.hs
+++ b/Control/Applicative.hs
@@ -42,6 +42,8 @@ import Control.Arrow
         (Arrow(arr, (&&&)), ArrowZero(zeroArrow), ArrowPlus((<+>)))
 import Control.Monad (liftM, ap, MonadPlus(..))
 import Control.Monad.Instances ()
+import Control.Monad.ST (ST)
+import qualified Control.Monad.ST.Lazy as Lazy (ST)
 import Data.Functor ((<$>), (<$))
 import Data.Monoid (Monoid(..))
 
@@ -149,6 +151,14 @@ instance Applicative IO where
         pure = return
         (<*>) = ap
 
+instance Applicative (ST s) where
+        pure = return
+        (<*>) = ap
+
+instance Applicative (Lazy.ST s) where
+        pure = return
+        (<*>) = ap
+
 #ifdef __GLASGOW_HASKELL__
 instance Applicative STM where
     pure = return