[Hs-Generics] Compile issue with multirec TH

[Dominique Devriese]

Hi,

I'm having a compile issue with multirec TH. Upon investigation, it
seems the same problem occurs in the compilation of one of the
examples in the multirec distribution:

	 domi at arial:/tmp> wget -q
http://hackage.haskell.org/packages/archive/multirec/0.4.1/multirec-0.4.1.tar.gz
	 domi at arial:/tmp> tar xzf multirec-0.4.1.tar.gz
	 domi at arial:/tmp> cd multirec-0.4.1/examples
	 domi at arial:/tmp/multirec-0.4.1/examples> ghc --make ASTTHUse.hs
	 [1 of 2] Compiling AST              ( AST.hs, AST.o )
	 [2 of 2] Compiling ASTTHUse         ( ASTTHUse.hs, ASTTHUse.o )
	 Loading package ghc-prim ... linking ... done.
	 Loading package integer-gmp ... linking ... done.
	 Loading package base ... linking ... done.
	 Loading package array-0.3.0.0 ... linking ... done.
	 Loading package containers-0.3.0.0 ... linking ... done.
	 Loading package pretty-1.0.1.1 ... linking ... done.
	 Loading package template-haskell ... linking ... done.
	 Loading package multirec-0.4.1 ... linking ... done.

	 ASTTHUse.hs:31:2:
	 GADT pattern match in non-rigid context for `Tag'
	 Probable solution: add a type signature for `to'
	 In the pattern: Tag L C K f0
	 In the pattern: L Tag L C K f0
	 In the definition of `to': to Expr L Tag L C K f0 = Const f0
	 domi at arial:/tmp/multirec-0.4.1/examples> ghc --version
	 The Glorious Glasgow Haskell Compilation System, version 6.12.1

Can you please tell me if this is a known problem and if so, if there
is a workaround?

Thanks in advance for your help!
Dominique