Bugs item #992200, was opened at 2004-07-16 09:11
Message generated for change (Comment added) made by simonpj
You can respond by visiting:
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Category: Template Haskell
Group: 6.2.1
Status: Open
Resolution: None
>Priority: 3
Submitted By: Mike Aizatsky (mm_aa)
Assigned to: Simon Peyton Jones (simonpj)
>Summary: Abysmal Template Haskell error message
Initial Comment:
Windows XP
D:\Tools\ghc>ghc-6.2.1\bin\ghc.exe -fglasgow-exts --make foo.hs
Chasing modules from: foo.hs
Compiling Any ( ./Any.hs, ./Any.o )
Compiling Foo ( foo.hs, foo.o )
Loading package base ... linking ... done.
Loading package haskell98 ... linking ... done.
Loading package haskell-src ... linking ... done.
ghc.exe: panic! (the `impossible' happened, GHC version 6.2.1):
Malformed predicate
module Any where
import Language.Haskell.THSyntax
genAny :: DecQ -> Q [Dec]
genAny decl =
do{
d <- decl
; case d of
ClassD _ name _ decls -> sequenceQ [genAnyClass
(name)
decls]
_ -> error "genAny can be applied to classes only"
}
genAnyClass :: String -> [Dec] -> DecQ
genAnyClass name decls =
do{
returnQ (DataD [forall] anyName [] [constructor] [])
}
where
anyName = "Any" ++ name ++ "1111"
constructor = NormalC anyName [(NotStrict, VarT "a")]
forall = ForallT [] [] (VarT "a")
module Foo where
import Any
class MyInterface a where
foo :: a -> Int
foo1 :: Int -> a -> Int
$(genAny (reifyDecl MyInterface))
----------------------------------------------------------------------
>Comment By: Simon Peyton Jones (simonpj)
Date: 2004-12-23 09:43
Message:
Logged In: YES
user_id=50165
Downgrading priority, and changing title
----------------------------------------------------------------------
Comment By: Mike Aizatsky (mm_aa)
Date: 2004-07-20 13:41
Message:
Logged In: YES
user_id=76543
Ok. I'll wait for 992199 fix to see how should I construct
the existential data types.
----------------------------------------------------------------------
Comment By: Simon Peyton Jones (simonpj)
Date: 2004-07-19 16:36
Message:
Logged In: YES
user_id=50165
You're constructing a syntactically invalid data type
declaration, looking like
data (forall. a) => T = MkT a
and not surprisingly that does not work. But the error
message is terrible, and we'll improve that, so I'm leaving the
bug open. It's a user error not a compiler failure.
----------------------------------------------------------------------
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