[project @ 2003-10-27 14:07:01 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcHsType.lhs

diff --git a/ghc/compiler/typecheck/TcHsType.lhs b/ghc/compiler/typecheck/TcHsType.lhs
index 7e9338f..b1f9e97 100644 (file)
--- a/ghc/compiler/typecheck/TcHsType.lhs
+++ b/ghc/compiler/typecheck/TcHsType.lhs
@@ -303,9 +303,16 @@ kcHsType (HsForAllTy exp tv_names context ty)
   = kcHsTyVars tv_names                $ \ tv_names' ->
     kcHsContext context                `thenM` \ ctxt' ->
     kcLiftedType ty            `thenM` \ ty' ->
-       -- The body of a forall must be of kind *
-       -- In principle, I suppose, we could allow unlifted types,
-       -- but it seems simpler to stick to lifted types for now.
+       -- The body of a forall must be a type, but in principle
+       -- there's no reason to prohibit *unlifted* types.
+       -- In fact, GHC can itself construct a function with an
+       -- unboxed tuple inside a for-all (via CPR analyis; see 
+       -- typecheck/should_compile/tc170)
+       --
+       -- Still, that's only for internal interfaces, which aren't
+       -- kind-checked, and it's a bit inconvenient to use kcTypeType
+       -- here (because it doesn't return the result kind), so I'm 
+       -- leaving it as lifted types for now.
     returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
 
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