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{-
------- Forwarded Message
Date: Wed, 30 Nov 1994 16:34:18 +0100
From: John Hughes <rjmh@cs.chalmers.se>
To: augustss@cs.chalmers.se, simonpj@dcs.gla.ac.uk
Subject: Nice little program
Lennart, Simon,
You might like to look at the fun little program below.
THUMBS DOWN to hbc for compiling it (it prints [72, 101, 108, 108, 111])
THUMBS UP to ghc for rejecting it --- but what an error message!
nhc and gofer both reject it with the right error message.
I haven't tried Yale Haskell.
Enjoy!
- ----------------------------
-}
class HasX a where
setX :: x->a->a
data X x = X x
instance HasX (X x) where
setX x (X _) = X x
changetype x = case setX x (X (error "change type!")) of X y->y
main = print (changetype "Hello" :: [Int])
{-
------- End of Forwarded Message
-}
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