Refactor, improve, and document the deriving mechanism

[ghc-hetmet.git] / compiler / types / Type.lhs

diff --git a/compiler/types/Type.lhs b/compiler/types/Type.lhs
index 8f23a35..aa3cd07 100644 (file)
--- a/compiler/types/Type.lhs
+++ b/compiler/types/Type.lhs
@@ -6,6 +6,13 @@
 Type - public interface
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- 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 Type (
         -- re-exports from TypeRep
        TyThing(..), Type, PredType(..), ThetaType, 
@@ -408,8 +415,14 @@ splitNewTyConApp_maybe (FunTy arg res)   = Just (funTyCon, [arg,res])
 splitNewTyConApp_maybe other         = Nothing
 
 newTyConInstRhs :: TyCon -> [Type] -> Type
-newTyConInstRhs tycon tys =
-    let (tvs, ty) = newTyConRhs tycon in substTyWith tvs tys ty
+-- Unwrap one 'layer' of newtype
+-- Use the eta'd version if possible
+newTyConInstRhs tycon tys 
+    = ASSERT2( equalLength tvs tys1, ppr tycon $$ ppr tys $$ ppr tvs )
+      mkAppTys (substTyWith tvs tys1 ty) tys2
+  where
+    (tvs, ty)    = newTyConEtadRhs tycon
+    (tys1, tys2) = splitAtList tvs tys
 \end{code}
 
 
@@ -1467,8 +1480,6 @@ isSuperKind other = False
 isKind :: Kind -> Bool
 isKind k = isSuperKind (typeKind k)
 
-
-
 isSubKind :: Kind -> Kind -> Bool
 -- (k1 `isSubKind` k2) checks that k1 <: k2
 isSubKind (TyConApp kc1 []) (TyConApp kc2 []) = kc1 `isSubKindCon` kc2