= updLclEnv (\ env -> env { tcl_untch = untch_tvs }) thing_inside
getUntouchables :: TcM TcTyVarSet
-getUntouchables
- = do { env <- getLclEnv; return (tcl_untch env) }
+getUntouchables = do { env <- getLclEnv; return (tcl_untch env) }
+ -- NB: no need to zonk this TcTyVarSet: they are, after all, untouchable!
isUntouchable :: TcTyVar -> TcM Bool
isUntouchable tv = do { env <- getLclEnv; return (tv `elemVarSet` tcl_untch env) }