[project @ 2003-05-13 11:42:47 by simonpj]

Generalise the type of listens slightly; a suggestion from Tom Pledger

diff --git a/Control/Monad/Writer.hs b/Control/Monad/Writer.hs
index 79ec97e..b941e65 100644 (file)
--- a/Control/Monad/Writer.hs
+++ b/Control/Monad/Writer.hs
@@ -59,7 +59,7 @@ class (Monoid w, Monad m) => MonadWriter w m | m -> w where
        listen :: m a -> m (a, w)
        pass   :: m (a, w -> w) -> m a
 
-listens :: (MonadWriter w m) => (w -> w) -> m a -> m (a, w)
+listens :: (MonadWriter w m) => (w -> b) -> m a -> m (a, b)
 listens f m = do
        (a, w) <- listen m
        return (a, f w)