Fix Trac #1746: make rule-matching work properly with Cast expressions

[ghc-hetmet.git] / compiler / specialise / SpecConstr.lhs

diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs
index 256674b..0478d2e 100644 (file)
--- a/compiler/specialise/SpecConstr.lhs
+++ b/compiler/specialise/SpecConstr.lhs
@@ -27,11 +27,11 @@ import CoreTidy             ( tidyRules )
 import PprCore         ( pprRules )
 import WwLib           ( mkWorkerArgs )
 import DataCon         ( dataConRepArity, dataConUnivTyVars )
-import Type            ( Type, tyConAppArgs )
-import Coercion                ( coercionKind )
+import Coercion        
+import Type            hiding( substTy )
 import Id              ( Id, idName, idType, isDataConWorkId_maybe, idArity,
                          mkUserLocal, mkSysLocal, idUnfolding, isLocalId )
-import Var             ( Var )
+import Var
 import VarEnv
 import VarSet
 import Name
@@ -1107,10 +1107,15 @@ argToPat in_scope val_env (Let _ arg) arg_occ
 
 argToPat in_scope val_env (Cast arg co) arg_occ
   = do { (interesting, arg') <- argToPat in_scope val_env arg arg_occ
-       ; if interesting then 
-               return (interesting, Cast arg' co)
-         else 
-               wildCardPat (snd (coercionKind co)) }
+       ; let (ty1,ty2) = coercionKind co
+       ; if not interesting then 
+               wildCardPat ty2
+         else do
+       { -- Make a wild-card pattern for the coercion
+         uniq <- getUniqueUs
+       ; let co_name = mkSysTvName uniq FSLIT("sg")
+             co_var = mkCoVar co_name (mkCoKind ty1 ty2)
+       ; return (interesting, Cast arg' (mkTyVarTy co_var)) } }
 
 {-     Disabling lambda specialisation for now
        It's fragile, and the spec_loop can be infinite