[project @ 2001-08-23 15:05:52 by simonpj]

[ghc-hetmet.git] / ghc / compiler / deSugar / DsCCall.lhs

diff --git a/ghc/compiler/deSugar/DsCCall.lhs b/ghc/compiler/deSugar/DsCCall.lhs
index eca07f7..8220405 100644 (file)
--- a/ghc/compiler/deSugar/DsCCall.lhs
+++ b/ghc/compiler/deSugar/DsCCall.lhs
@@ -31,7 +31,7 @@ import TcType         ( Type, isUnLiftedType, mkFunTys, mkFunTy,
                          isBoolTy, isUnitTy, isPrimitiveType,
                          tcSplitTyConApp_maybe
                        )
-import Type            ( splitTyConApp_maybe, repType, eqType )        -- Sees the representation type
+import Type            ( repType, eqType )     -- Sees the representation type
 import PrimOp          ( PrimOp(TouchOp) )
 import TysPrim         ( realWorldStatePrimTy,
                          byteArrayPrimTyCon, mutableByteArrayPrimTyCon,
@@ -153,7 +153,6 @@ unboxArg arg
                              prim_arg 
                             [(DEFAULT,[],body)])
 
-  -- Newtypes 
   -- Data types with a single constructor, which has a single, primitive-typed arg
   -- This deals with Int, Float etc
   | is_product_type && data_con_arity == 1 
@@ -165,6 +164,9 @@ unboxArg arg
     )
 
   -- Byte-arrays, both mutable and otherwise; hack warning
+  -- We're looking for values of type ByteArray, MutableByteArray
+  --   data ByteArray          ix = ByteArray        ix ix ByteArray#
+  --   data MutableByteArray s ix = MutableByteArray ix ix (MutableByteArray# s)
   | is_product_type &&
     data_con_arity == 3 &&
     maybeToBool maybe_arg3_tycon &&
@@ -183,7 +185,9 @@ unboxArg arg
   where
     arg_ty                                     = repType (exprType arg)
        -- The repType looks through any newtype or 
-       -- implicit-parameter wrappings on the argument.  
+       -- implicit-parameter wrappings on the argument;
+       -- this is necessary, because isBoolTy (in particular) does not.
+
     maybe_product_type                                 = splitProductType_maybe arg_ty
     is_product_type                            = maybeToBool maybe_product_type
     Just (_, _, data_con, data_con_arg_tys)    = maybe_product_type
@@ -217,6 +221,8 @@ boxResult :: [Id] -> Type -> DsM (Type, CoreExpr -> CoreExpr)
 
 boxResult arg_ids result_ty
   = case tcSplitTyConApp_maybe result_ty of
+       -- This split absolutely has to be a tcSplit, because we must
+       -- see the IO type; and it's a newtype which is transparent to splitTyConApp.
 
        -- The result is IO t, so wrap the result in an IO constructor
        Just (io_tycon, [io_res_ty]) | io_tycon `hasKey` ioTyConKey
@@ -305,7 +311,7 @@ resultWrapper result_ty
   | isUnitTy result_ty_rep
   = (Nothing, \e -> Var unitDataConId)
 
-  -- Base case 3: the boolean type ()
+  -- Base case 3: the boolean type
   | isBoolTy result_ty_rep
   = (Just intPrimTy, \e -> Case e (mkWildId intPrimTy)
                                  [(DEFAULT             ,[],Var trueDataConId ),
@@ -324,6 +330,5 @@ resultWrapper result_ty
   | otherwise
   = pprPanic "resultWrapper" (ppr result_ty)
   where
-    result_ty_rep = repType result_ty
-
+    result_ty_rep = repType result_ty  -- Look through any newtypes/implicit parameters
 \end{code}