Bug fix in the new HscMain code.

[ghc-hetmet.git] / ghc / compiler / coreSyn / CoreUtils.lhs

diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs
index a8c7eae..e358be4 100644 (file)
--- a/ghc/compiler/coreSyn/CoreUtils.lhs
+++ b/ghc/compiler/coreSyn/CoreUtils.lhs
@@ -46,10 +46,13 @@ import Var          ( Var )
 import VarSet          ( unionVarSet )
 import VarEnv
 import Name            ( hashName )
-import Packages                ( isDllName, HomeModules )
+import Packages                ( HomeModules )
+#if mingw32_TARGET_OS
+import Packages                ( isDllName )
+#endif
 import Literal         ( hashLiteral, literalType, litIsDupable, 
                          litIsTrivial, isZeroLit, Literal( MachLabel ) )
-import DataCon         ( DataCon, dataConRepArity, dataConArgTys,
+import DataCon         ( DataCon, dataConRepArity, dataConInstArgTys,
                          isVanillaDataCon, dataConTyCon )
 import PrimOp          ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap )
 import Id              ( Id, idType, globalIdDetails, idNewStrictness, 
@@ -66,7 +69,6 @@ import Type           ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
                          splitTyConApp_maybe, coreEqType, funResultTy, applyTy
                        )
 import TyCon           ( tyConArity )
--- gaw 2004
 import TysWiredIn      ( boolTy, trueDataCon, falseDataCon )
 import CostCentre      ( CostCentre )
 import BasicTypes      ( Arity )
@@ -453,7 +455,7 @@ idAppIsCheap id n_val_args
   | otherwise 
   = case globalIdDetails id of
        DataConWorkId _ -> True
-       RecordSelId _ _ -> n_val_args == 1      -- I'm experimenting with making record selection
+       RecordSelId {}  -> n_val_args == 1      -- I'm experimenting with making record selection
        ClassOpId _     -> n_val_args == 1      -- look cheap, so we will substitute it inside a
                                                -- lambda.  Particularly for dictionary field selection.
                -- BUT: Take care with (sel d x)!  The (sel d) might be cheap, but
@@ -649,7 +651,7 @@ exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
     let
        arity            = tyConArity tc
        val_args         = drop arity args
-       to_arg_tys       = dataConArgTys dc tc_arg_tys
+       to_arg_tys       = dataConInstArgTys dc tc_arg_tys
        mk_coerce ty arg = mkCoerce ty arg
        new_val_args     = zipWith mk_coerce to_arg_tys val_args
     in
@@ -754,6 +756,27 @@ consider
 This should diverge!  But if we eta-expand, it won't.   Again, we ignore this
 "problem", because being scrupulous would lose an important transformation for
 many programs.
+
+
+4. Newtypes
+
+Non-recursive newtypes are transparent, and should not get in the way.
+We do (currently) eta-expand recursive newtypes too.  So if we have, say
+
+       newtype T = MkT ([T] -> Int)
+
+Suppose we have
+       e = coerce T f
+where f has arity 1.  Then: etaExpandArity e = 1; 
+that is, etaExpandArity looks through the coerce.
+
+When we eta-expand e to arity 1: eta_expand 1 e T
+we want to get:                 coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
+
+HOWEVER, note that if you use coerce bogusly you can ge
+       coerce Int negate
+And since negate has arity 2, you might try to eta expand.  But you can't
+decopose Int to a function type.   Hence the final case in eta_expand.
 -}
 
 
@@ -946,7 +969,13 @@ eta_expand n us expr ty
 
        case splitRecNewType_maybe ty of {
          Just ty' -> mkCoerce2 ty ty' (eta_expand n us (mkCoerce2 ty' ty expr) ty') ;
-         Nothing  -> pprTrace "Bad eta expand" (ppr n $$ ppr expr $$ ppr ty) expr
+         Nothing  -> 
+
+       -- We have an expression of arity > 0, but its type isn't a function
+       -- This *can* legitmately happen: e.g.  coerce Int (\x. x)
+       -- Essentially the programmer is playing fast and loose with types
+       -- (Happy does this a lot).  So we simply decline to eta-expand.
+       expr
        }}}
 \end{code}