Bugs item #1119221, was opened at 2005-02-09 03:07
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Category: Compiler (Type checker)
Group: 6.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Rebindable syntax doesn't work as advertised
Initial Comment:
--
-- According to section 7.3.5. Rebindable syntax in the
user's manual
-- this should work (unless I totally misunderstood it).
-- It doesn't.
--
-- Compile with -fno-implicit-prelude
--
-- Lennart
--
import Prelude hiding(Monad(..))
class B a where
b :: a
instance B Bool where
b = False
class M m where
return :: a -> m a
(>>=) :: (B a) => m a -> (a -> m b) -> m b
(>>) :: (B a) => m a -> m b -> m b
fail :: String -> m a
p >> q = p >>= \ _ -> q
fail s = error s
instance M Maybe where
return x = Just x
(>>=) = error "bind"
test :: Maybe Bool
test = do
x <- return True
return (x && x)
unJust (Just x) = x
main = print (unJust test)
----------------------------------------------------------------------
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