FIX Trac #1806: test for correct arity for datacon in infix pattern patch

[ghc-hetmet.git] / compiler / typecheck / TcPat.lhs

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index fca172f..f220154 100644 (file)
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -717,9 +717,10 @@ tcConArgs data_con arg_tys (PrefixCon arg_pats) pstate thing_inside
     con_arity  = dataConSourceArity data_con
     no_of_args = length arg_pats
 
-tcConArgs data_con [arg_ty1,arg_ty2] (InfixCon p1 p2) pstate thing_inside
+tcConArgs data_con arg_tys (InfixCon p1 p2) pstate thing_inside
   = do { checkTc (con_arity == 2)      -- Check correct arity
                  (arityErr "Constructor" data_con con_arity 2)
+       ; let [arg_ty1,arg_ty2] = arg_tys       -- This can't fail after the arity check
        ; ([p1',p2'], tvs, res) <- tcMultiple tcConArg [(p1,arg_ty1),(p2,arg_ty2)]
                                              pstate thing_inside
        ; return (InfixCon p1' p2', tvs, res) }