I asked previously about an internal error that occured in the version of
Hugs98
that I compiled myself. I solved my problems by downloading precompiled
binaries.
My programs worked fine with these precompiled binaries, but
now I managed to write something which causes internal error in
the precompiled interpreter. The code is at the end of message.
It is the rApply method makes the problems. My intention with rApply was to
implement call-by-name application in a modular interpreter. I tried to
write it without anotations first, but the typechecker complains. So I put
anotations and got the internal error:
__ __ __ __ ____ ___ _________________________________________
|| || || || || || ||__ Hugs 98: Based on the Haskell 98 standard
||___|| ||__|| ||__|| __|| Copyright (c) 1994-1999
||---|| ___|| World Wide Web: http://haskell.org/hugs
|| || Report bugs to: [EMAIL PROTECTED]
|| || Version: February 2000 _________________________________________
Hugs mode: Restart with command line option +98 for Haskell 98 mode
Reading file "e:\lang\hugs98\lib\Prelude.hs":
Reading file "main.hs":
Type checking
INTERNAL ERROR: findBtyvsInt
Prelude>
I started Hugs with a batch file:
@echo off
set HUGSPATH=e:\lang\hugs98\lib;e:\lang\hugs98\lib\exts;e:\lang\hugs98\lib\hugs
set EDITOR=uedit32 +s
e:\lang\hugs98\hugs.exe -P%HUGSPATH% -E%EDITOR% -98 +o -c100 %1 %2
The same happens on my friend's machine. I'm using Windows97, and he uses
Windows98. Would you be so kind and try the short program bellow on your
version of interpreter for the start? I have tried many other programs in
this interpreter
and they worked fine. My version is from February 2000.
[The problematic code follows]
---------------------------------------------------------------------
module Main where
class Subtype sub sup where
inj :: sub -> sup
prj :: sup -> Maybe sub
class Monad m => EnvMonad e m where
rdEnv :: m e
inEnv :: e -> m a -> m a
mprj :: (Monad m, Subtype sub sup) => m sup -> m sub
mprj ma = do x <- ma
case prj x of
Just a -> return a
Nothing -> error "Projection failed"
newtype FMap a b = FM {unFM :: [(a,b)]}
class (EnvMonad (FMap String (m dom)) m,
Subtype (m dom -> m dom) dom)
=> Reflexive dom m where
rApply :: m dom -> m dom -> m dom
instance (EnvMonad (FMap String (m dom)) m,
Subtype (m dom -> m dom) dom)
=> Reflexive dom m where
{- This does not type check
rApply mf mx = do f <- mprj mf
env <- rdEnv
f (inEnv env mx)
-}
-- I tried to help the type checker, but all i got was
-- INTERNAL ERROR: findBtyvsInt
rApply mf mx = do (f :: m a -> m a) <- mprj mf
(env :: FMap String (m dom)) <- rdEnv
f (inEnv env mx)
-- end of module Main ---------------------------------------------
