{-# LANGUAGE TupleSections #-}
{-# OPTIONS_HADDOCK show-extensions #-}
module GHC.TypeLits.Extra.Solver
( plugin )
where
import Control.Monad ((<=<))
import Control.Monad.Trans.Maybe (MaybeT (..))
import Data.Maybe (catMaybes)
import GHC.TcPluginM.Extra (evByFiat, lookupModule, lookupName,
tracePlugin)
import FastString (fsLit)
import Module (mkModuleName)
import OccName (mkTcOcc)
import Outputable (Outputable (..), (<+>), ($$), text)
import Plugins (Plugin (..), defaultPlugin)
import TcEvidence (EvTerm)
import TcPluginM (TcPluginM, tcLookupTyCon, tcPluginTrace, zonkCt)
import TcRnTypes (Ct, TcPlugin(..), TcPluginResult (..), ctEvidence, ctEvPred,
isWanted)
import TcType (typeKind)
import Type (EqRel (NomEq), Kind, PredTree (EqPred), classifyPredType,
eqType)
import TysWiredIn (typeNatKind)
import GHC.TypeLits.Extra.Solver.Operations
import GHC.TypeLits.Extra.Solver.Unify
plugin :: Plugin
plugin = defaultPlugin { tcPlugin = const $ Just normalisePlugin }
normalisePlugin :: TcPlugin
normalisePlugin = tracePlugin "ghc-typelits-extra"
TcPlugin { tcPluginInit = lookupExtraDefs
, tcPluginSolve = decideEqualSOP
, tcPluginStop = const (return ())
}
decideEqualSOP :: ExtraDefs -> [Ct] -> [Ct] -> [Ct] -> TcPluginM TcPluginResult
decideEqualSOP _ _givens _deriveds [] = return (TcPluginOk [] [])
decideEqualSOP defs givens _deriveds wanteds = do
let wanteds' = filter (isWanted . ctEvidence) wanteds
unit_wanteds <- catMaybes <$> mapM (runMaybeT . toNatEquality defs) wanteds'
case unit_wanteds of
[] -> return (TcPluginOk [] [])
_ -> do
unit_givens <- catMaybes <$> mapM ((runMaybeT . toNatEquality defs) <=< zonkCt) givens
sr <- simplifyExtra (unit_givens ++ unit_wanteds)
tcPluginTrace "normalised" (ppr sr)
case sr of
Simplified evs -> return (TcPluginOk (filter (isWanted . ctEvidence . snd) evs) [])
Impossible eq -> return (TcPluginContradiction [fromNatEquality eq])
type NatEquality = (Ct,ExtraOp,ExtraOp)
data SimplifyResult
= Simplified [(EvTerm,Ct)]
| Impossible NatEquality
instance Outputable SimplifyResult where
ppr (Simplified evs) = text "Simplified" $$ ppr evs
ppr (Impossible eq) = text "Impossible" <+> ppr eq
simplifyExtra :: [NatEquality] -> TcPluginM SimplifyResult
simplifyExtra eqs = tcPluginTrace "simplifyExtra" (ppr eqs) >> simples [] eqs
where
simples :: [Maybe (EvTerm, Ct)] -> [NatEquality] -> TcPluginM SimplifyResult
simples evs [] = return (Simplified (catMaybes evs))
simples evs (eq@((ct,u,v)):eqs') = do
ur <- unifyExtra ct u v
tcPluginTrace "unifyExtra result" (ppr ur)
case ur of
Win -> simples (((,) <$> evMagic ct <*> pure ct):evs) eqs'
Lose -> return (Impossible eq)
Draw -> simples evs eqs'
toNatEquality :: ExtraDefs -> Ct -> MaybeT TcPluginM NatEquality
toNatEquality defs ct = case classifyPredType $ ctEvPred $ ctEvidence ct of
EqPred NomEq t1 t2
| isNatKind (typeKind t1) || isNatKind (typeKind t2)
-> (ct,,) <$> normaliseNat defs t1 <*> normaliseNat defs t2
_ -> fail "Nothing"
where
isNatKind :: Kind -> Bool
isNatKind = (`eqType` typeNatKind)
fromNatEquality :: NatEquality -> Ct
fromNatEquality (ct, _, _) = ct
lookupExtraDefs :: TcPluginM ExtraDefs
lookupExtraDefs = do
md <- lookupModule myModule myPackage
ExtraDefs <$> look md "Div"
<*> look md "Mod"
<*> look md "FLog"
<*> look md "CLog"
<*> look md "Log"
<*> look md "GCD"
<*> look md "LCM"
where
look md s = tcLookupTyCon =<< lookupName md (mkTcOcc s)
myModule = mkModuleName "GHC.TypeLits.Extra"
myPackage = fsLit "ghc-typelits-extra"
evMagic :: Ct -> Maybe EvTerm
evMagic ct = case classifyPredType $ ctEvPred $ ctEvidence ct of
EqPred NomEq t1 t2 -> Just (evByFiat "ghc-typelits-extra" t1 t2)
_ -> Nothing