Fixed remaining warning in coreSyn/MkExternalCore

There was a (suppressed) warning about an incomplete pattern match in make_alt. This was because the DEFAULT alt never has variable bindings. I thought it would be better to check that case and panic if it happens than to have an incomplete pattern. It's still not great, but at least now we don't have to suppress any warnings in this file.

diff --git a/compiler/coreSyn/MkExternalCore.lhs b/compiler/coreSyn/MkExternalCore.lhs
index 78008e1..faa6bb9 100644 (file)
--- a/compiler/coreSyn/MkExternalCore.lhs
+++ b/compiler/coreSyn/MkExternalCore.lhs
@@ -2,13 +2,6 @@
 % (c) The University of Glasgow 2001-2006
 %
 \begin{code}
-{-# OPTIONS -fno-warn-incomplete-patterns #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
---     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
 module MkExternalCore (
        emitExternalCore
 ) where
@@ -138,8 +131,13 @@ make_alt (DataAlt dcon, vs, e) =
            (map make_vbind vbs)
           (make_exp e)    
        where (tbs,vbs) = span isTyVar vs
-make_alt (LitAlt l,_,e) = C.Alit (make_lit l) (make_exp e)
-make_alt (DEFAULT,[],e) = C.Adefault (make_exp e)
+make_alt (LitAlt l,_,e)   = C.Alit (make_lit l) (make_exp e)
+make_alt (DEFAULT,[],e)   = C.Adefault (make_exp e)
+-- This should never happen, as the DEFAULT alternative binds no variables,
+-- but we might as well check for it:
+make_alt a@(DEFAULT,_ ,_) = pprPanic ("MkExternalCore: make_alt: DEFAULT "
+             ++ "alternative had a non-empty var list") (ppr a)
+
 
 make_lit :: Literal -> C.Lit
 make_lit l =