-- (mkPiType now in CoreUtils)
-Applying a for-all to its arguments. Lift usage annotation as required.
+applyTy, applyTys
+~~~~~~~~~~~~~~~~~
+Instantiate a for-all type with one or more type arguments.
+Used when we have a polymorphic function applied to type args:
+ f t1 t2
+Then we use (applyTys type-of-f [t1,t2]) to compute the type of
+the expression.
\begin{code}
applyTy :: Type -> Type -> Type
applyTy other arg = panic "applyTy"
applyTys :: Type -> [Type] -> Type
-applyTys orig_fun_ty arg_tys
- = substTyWith tvs arg_tys ty
- where
- (tvs, ty) = split orig_fun_ty arg_tys
-
- split fun_ty [] = ([], fun_ty)
- split (NoteTy _ fun_ty) args = split fun_ty args
- split (SourceTy p) args = split (sourceTypeRep p) args
- split (ForAllTy tv fun_ty) (arg:args) = case split fun_ty args of
- (tvs, ty) -> (tv:tvs, ty)
- split other_ty args = panic "applyTys"
- -- No show instance for Type yet
+-- This function is interesting because
+-- a) the function may have more for-alls than there are args
+-- b) less obviously, it may have fewer for-alls
+-- For case (b) think of
+-- applyTys (forall a.a) [forall b.b, Int]
+-- This really can happen, via dressing up polymorphic types with newtype
+-- clothing. Here's an example:
+-- newtype R = R (forall a. a->a)
+-- foo = case undefined :: R of
+-- R f -> f ()
+
+applyTys orig_fun_ty [] = orig_fun_ty
+applyTys orig_fun_ty arg_tys
+ | n_tvs == n_args -- The vastly common case
+ = substTyWith tvs arg_tys rho_ty
+ | n_tvs > n_args -- Too many for-alls
+ = substTyWith (take n_args tvs) arg_tys
+ (mkForAllTys (drop n_args tvs) rho_ty)
+ | otherwise -- Too many type args
+ = ASSERT2( n_tvs > 0, pprType orig_fun_ty ) -- Zero case gives infnite loop!
+ applyTys (substTyWith tvs (take n_tvs arg_tys) rho_ty)
+ (drop n_tvs arg_tys)
+ where
+ (tvs, rho_ty) = splitForAllTys orig_fun_ty
+ n_tvs = length tvs
+ n_args = length arg_tys
\end{code}