module GHC.TypeLits.Normalise
( plugin )
where
import Data.Maybe (catMaybes, mapMaybe)
import Coercion (Role (Nominal), mkUnivCo)
import FastString (fsLit)
import Outputable (Outputable (..), (<+>), ($$), text)
import Plugins (Plugin (..), defaultPlugin)
import TcEvidence (EvTerm (EvCoercion), TcCoercion (..))
import TcPluginM (TcPluginM, tcPluginTrace, unsafeTcPluginTcM, zonkCt)
import qualified TcMType
import TcRnTypes (Ct, CtEvidence (..), CtOrigin, TcPlugin(..),
TcPluginResult(..), ctEvidence, ctEvPred,
ctLoc, ctLocOrigin, isGiven, isWanted, mkNonCanonical)
import TcType (mkEqPred, typeKind)
import Type (EqRel (NomEq), Kind, PredTree (EqPred), PredType, Type,
TyVar, classifyPredType, mkTyVarTy)
import TysWiredIn (typeNatKind)
import GHC.TypeLits.Normalise.Unify
plugin :: Plugin
plugin = defaultPlugin { tcPlugin = const $ Just normalisePlugin }
normalisePlugin :: TcPlugin
normalisePlugin =
TcPlugin { tcPluginInit = return ()
, tcPluginSolve = decideEqualSOP
, tcPluginStop = const (return ())
}
decideEqualSOP :: () -> [Ct] -> [Ct] -> [Ct] -> TcPluginM TcPluginResult
decideEqualSOP _ _givens _deriveds [] = return (TcPluginOk [] [])
decideEqualSOP _ givens _deriveds wanteds = do
let unit_wanteds = mapMaybe toNatEquality wanteds
case unit_wanteds of
[] -> return (TcPluginOk [] [])
_ -> do
unit_givens <- mapMaybe toNatEquality <$> mapM zonkCt givens
sr <- simplifyNats (unit_givens ++ unit_wanteds)
tcPluginTrace "normalised" (ppr sr)
case sr of
Simplified subst evs ->
TcPluginOk (filter (isWanted . ctEvidence . snd) evs) <$>
mapM substItemToCt (filter (isWanted . ctEvidence . siNote) subst)
Impossible eq -> return (TcPluginContradiction [fromNatEquality eq])
substItemToCt :: SubstItem TyVar Type Ct -> TcPluginM Ct
substItemToCt si
| isGiven (ctEvidence ct) = return $ mkNonCanonical
$ CtGiven predicate
(evByFiat "units" (ty1, ty2)) loc
| otherwise = newSimpleWanted (ctLocOrigin loc) predicate
where
predicate = mkEqPred ty1 ty2
ty1 = mkTyVarTy (siVar si)
ty2 = reifySOP (siSOP si)
ct = siNote si
loc = ctLoc ct
type NatEquality = (Ct,CoreSOP,CoreSOP)
fromNatEquality :: NatEquality -> Ct
fromNatEquality (ct, _, _) = ct
data SimplifyResult
= Simplified CoreSubst [(EvTerm,Ct)]
| Impossible NatEquality
instance Outputable SimplifyResult where
ppr (Simplified subst evs) = text "Simplified" $$ ppr subst $$ ppr evs
ppr (Impossible eq) = text "Impossible" <+> ppr eq
simplifyNats :: [NatEquality] -> TcPluginM SimplifyResult
simplifyNats eqs = tcPluginTrace "simplifyNats" (ppr eqs) >> simples [] [] [] eqs
where
simples :: CoreSubst -> [Maybe (EvTerm, Ct)] -> [NatEquality]
-> [NatEquality] -> TcPluginM SimplifyResult
simples subst evs _xs [] = return (Simplified subst (catMaybes evs))
simples subst evs xs (eq@(ct,u,v):eqs') = do
ur <- unifyNats ct (substsSOP subst u) (substsSOP subst v)
tcPluginTrace "unifyNats result" (ppr ur)
case ur of
Win -> simples subst (((,) <$> evMagic ct <*> pure ct):evs) []
(xs ++ eqs')
Lose -> return (Impossible eq)
Draw [] -> simples subst evs (eq:xs) eqs'
Draw subst' -> simples (substsSubst subst' subst ++ subst') evs [eq]
(xs ++ eqs')
toNatEquality :: Ct -> Maybe NatEquality
toNatEquality ct = case classifyPredType $ ctEvPred $ ctEvidence ct of
EqPred NomEq t1 t2
| isNatKind (typeKind t1) || isNatKind (typeKind t1)
-> Just (ct,normaliseNat t1,normaliseNat t2)
_ -> Nothing
where
isNatKind :: Kind -> Bool
isNatKind = (== typeNatKind)
newSimpleWanted :: CtOrigin -> PredType -> TcPluginM Ct
newSimpleWanted orig = unsafeTcPluginTcM . TcMType.newSimpleWanted orig
evMagic :: Ct -> Maybe EvTerm
evMagic ct = case classifyPredType $ ctEvPred $ ctEvidence ct of
EqPred NomEq t1 t2 -> Just (evByFiat "tylits_magic" (t1, t2))
_ -> Nothing
evByFiat :: String -> (Type, Type) -> EvTerm
evByFiat name (t1,t2) = EvCoercion $ TcCoercion
$ mkUnivCo (fsLit name) Nominal t1 t2