where
bndrs = bndrNames mono_infos
sigs = [sig | (_, Just sig, _) <- mono_infos]
- tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos
- -- NB: exactTyVarsOfType; see Note [Silly type synonym]
- -- near defn of TcType.exactTyVarsOfType
+ get_tvs | isTopLevel top_lvl = tyVarsOfType -- See Note [Silly type synonym] in TcType
+ | otherwise = exactTyVarsOfType
+ tau_tvs = foldr (unionVarSet . get_tvs . getMonoType) emptyVarSet mono_infos
is_mono_sig sig = null (sig_theta sig)
doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs
which type variables are mentioned in a type. It's also used in the
smart-app checking code --- see TcExpr.tcIdApp
+On the other hand, consider a *top-level* definition
+ f = (\x -> x) :: T a -> T a
+If we don't abstract over 'a' it'll get fixed to GHC.Prim.Any, and then
+if we have an application like (f "x") we get a confusing error message
+involving Any. So the conclusion is this: when generalising
+ - at top level use tyVarsOfType
+ - in nested bindings use exactTyVarsOfType
+See Trac #1813 for example.
+
\begin{code}
exactTyVarsOfType :: TcType -> TyVarSet
-- Find the free type variables (of any kind)