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module Internal.Type (substType) where
import Data.Maybe (fromMaybe)
import GhcPlugins hiding (TcPlugin, mkSubst)
import TcType (TcType)
import TyCoRep (Type (..))
-- | Apply substitutions in Types
--
-- __NB:__ Doesn't substitute under binders
substType
:: [(TcTyVar, TcType)]
-> TcType
-> TcType
substType subst tv@(TyVarTy v) =
fromMaybe tv (lookup v subst)
substType subst (AppTy t1 t2) =
AppTy (substType subst t1) (substType subst t2)
substType subst (TyConApp tc xs) =
TyConApp tc (map (substType subst) xs)
substType _subst t@(ForAllTy _tv _ty) =
-- TODO: Is it safe to do "dumb" substitution under binders?
-- ForAllTy tv (substType subst ty)
t
substType subst (FunTy af t1 t2) =
FunTy af (substType subst t1) (substType subst t2)
substType _ l@(LitTy _) = l
substType subst (CastTy ty co) =
CastTy (substType subst ty) co
substType _ co@(CoercionTy _) = co
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