Hi,
while trying to compile the attached file MonadT.hs I got the following error:
ghc -fglasgow-exts -c -o MonadT.o MonadT.hs
ghc-5.02: panic! (the `impossible' happened, GHC version 5.02):
coreSyn/Subst.lhs:387: Non-exhaustive patterns in function zip_ty_env
Please report it as a compiler bug to [EMAIL PROTECTED],
or http://sourceforge.net/projects/ghc/.
--
uname -a
Linux hobbes 2.2.17 #2 SMP Sun Dec 3 22:42:15 CET 2000 i686 unknown
gcc -v
Reading specs from /usr/lib/gcc-lib/i386-linux/2.95.2/specs
gcc version 2.95.2 20000220 (Debian GNU/Linux)
output while running with -v enabled:
ghc -fglasgow-exts -v -c -o MonadT.o MonadT.hs
Glasgow Haskell Compiler, Version 5.02, for Haskell 98, compiled by GHC
version 5.02
Using package config file: /usr/lib/ghc-5.02/package.conf
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Hsc static flags: -static -fignore-interface-pragmas -fomit-interface-pragmas
-fdo-lambda-eta-expansion -flet-no-escape
*** Checking old interface for hs = Just "MonadT.hs", hspp = Just "MonadT.hs":
Compiling MonadT ( MonadT.hs, MonadT.o )
*** Parser:
*** Renamer:
*** Typechecker:
*** Deleting temp files
Deleting: /tmp/ghc32713.s /tmp/ghc32713.hspp
Warning: deleting non-existent /tmp/ghc32713.s
Warning: deleting non-existent /tmp/ghc32713.hspp
ghc-5.02: panic! (the `impossible' happened, GHC version 5.02):
coreSyn/Subst.lhs:387: Non-exhaustive patterns in function zip_ty_env
Please report it as a compiler bug to [EMAIL PROTECTED],
or http://sourceforge.net/projects/ghc/.
-- Monad transformers
-- from an article by Sheng Liang, Paul Hudak, Mark Jones 1995
module MonadT where
--- Monad transformer
class (Monad m, Monad (t m)) => MonadT t m where
lift :: m a -> t m a
-- lift must fulfill the following "Monad Transformer Laws":
-- lift . return_m = return_tm
-- lift (m >>=_m k) = (lift m) >>=_tm (lift . k)
--- State monad transformer
type StateT s m a = s -> m (s, a)
-- monad definition
instance Monad m => Monad (StateT s m) where
return x = \s -> return (s, x)
m >>= k = \s0 -> do (s1, a) <- m s0; k a s1
-- state transformer
instance (Monad m, Monad (StateT s m)) => MonadT (StateT s) m where
lift m = \s -> do x <- m; return (s, x)
--- State monad
class Monad m => StateMonad s m where
update :: (s -> s) -> m s -- update state
property :: (s -> a) -> m a -- extract property of state
apply :: s -> m s -> s -- apply to initial state, answer resulting state
state :: m s -- extract state
state = property id
instance Monad m => StateMonad s (StateT s m) where
update f = \s -> return (f s, s)
property p = \s -> return (s, p s)
apply s m = fst (m s)
