FW: [ ghc-Bugs-992200 ] Template crash on constructing existential datatype

Dear Template Haskell folk

This SourceForge bug is another example of the bad things that happen
when:

- a TH program constructs a syntactically invalid program
- and then splices it in

The trouble is that Convert.convertToHsExpr :: TH.Exp -> LHsExpr RdrName
is a pure function, and fails "hard" with a panic, whereas it should
really be in the TcM monad, and fail in the way any other type error
fails.  It's a user error, and should not show up as a panic.

Would anyone like to fix hsSyn/Convert.lhs so that it lives in the Tc
monad?  The call (in TcSplice) is easily changed.  It'd probably make
sense to move it from hsSyn/ to typecheck/

I'm thinking about putting types in the syntax tree, so if others can
help out with tidying up like this, it'd be great.

Simon

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
SourceForge.net
Sent: 16 July 2004 10:11
To: [email protected]
Subject: [ ghc-Bugs-992200 ] Template crash on constructing existential
datatype

Bugs item #992200, was opened at 2004-07-16 09:11
Message generated for change (Tracker Item Submitted) made by Item
Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=108032&aid=992200&grou
p_id=8032

Category: Compiler
Group: 6.2.1
Status: Open
Resolution: None
Priority: 5
Submitted By: Mike Aizatsky (mm_aa)
Assigned to: Nobody/Anonymous (nobody)
Summary: Template crash on constructing existential data type

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))


----------------------------------------------------------------------

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https://sourceforge.net/tracker/?func=detail&atid=108032&aid=992200&grou
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