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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
------------------------------------------------------------------------------
-- The MIT License (MIT)
--
-- Copyright (c) 2017 Luka Horvat
--
-- Permission is hereby granted, free of charge, to any person obtaining a copy
-- of this software and associated documentation files (the "Software"), to
-- deal in the Software without restriction, including without limitation the
-- rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
-- sell copies of the Software, and to permit persons to whom the Software is
-- furnished to do so, subject to the following conditions:
--
-- The above copyright notice and this permission notice shall be included in
-- all copies or substantial portions of the Software.
--
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-- FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
-- IN THE SOFTWARE.
--
------------------------------------------------------------------------------
--
-- This module is heavily based on 'Control.Effects.Plugin' from the
-- 'simple-effects' package, originally by Luka Horvat.
--
-- https://gitlab.com/LukaHorvat/simple-effects/commit/966ce80b8b5777a4bd8f87ffd443f5fa80cc8845#f51c1641c95dfaa4827f641013f8017e8cd02aab
module Polysemy.Plugin.Fundep (fundepPlugin) where
import Class
import CoAxiom
import Control.Applicative
import Control.Monad
import Data.Bifunctor
import Data.Bool
import Data.Function (on)
import Data.IORef
import Data.List
import Data.Maybe
import qualified Data.Set as S
import FastString (fsLit)
import GHC (ModuleName)
import GHC.TcPluginM.Extra (lookupModule, lookupName)
import Module (mkModuleName)
import OccName (mkTcOcc)
import TcPluginM (TcPluginM, tcLookupClass, tcPluginIO)
import TcRnTypes
import TcSMonad hiding (tcLookupClass)
import TyCoRep (Type (..))
import Type
polysemyInternalUnion :: ModuleName
polysemyInternalUnion = mkModuleName "Polysemy.Internal.Union"
fundepPlugin :: TcPlugin
fundepPlugin = TcPlugin
{ tcPluginInit = do
md <- lookupModule polysemyInternalUnion (fsLit "polysemy")
monadEffectTcNm <- lookupName md (mkTcOcc "Find")
(,) <$> tcPluginIO (newIORef S.empty)
<*> tcLookupClass monadEffectTcNm
, tcPluginSolve = solveFundep
, tcPluginStop = const (return ()) }
allMonadEffectConstraints :: Class -> [Ct] -> [(CtLoc, (Type, Type, Type))]
allMonadEffectConstraints cls cts =
[ (ctLoc cd, (effName, eff, r))
| cd@CDictCan{cc_class = cls', cc_tyargs = [_, r, eff]} <- cts
, cls == cls'
, let effName = getEffName eff
]
singleListToJust :: [a] -> Maybe a
singleListToJust [a] = Just a
singleListToJust _ = Nothing
findMatchingEffectIfSingular :: (Type, Type, Type) -> [(Type, Type, Type)] -> Maybe Type
findMatchingEffectIfSingular (effName, _, mon) ts = singleListToJust
[ eff'
| (effName', eff', mon') <- ts
, eqType effName effName'
, eqType mon mon' ]
getEffName :: Type -> Type
getEffName t = fst $ splitAppTys t
canUnifyRecursive :: SolveContext -> Type -> Type -> Bool
canUnifyRecursive solve_ctx = go True
where
-- It's only OK to solve a polymorphic "given" if we're in the context of
-- an interpreter, because it's not really a given!
poly_given_ok :: Bool
poly_given_ok =
case solve_ctx of
InterpreterUse _ -> True
FunctionDef -> False
-- On the first go around, we don't want to unify effects with tyvars, but
-- we _do_ want to unify their arguments, thus 'is_first'.
go :: Bool -> Type -> Type -> Bool
go is_first wanted given =
let (w, ws) = splitAppTys wanted
(g, gs) = splitAppTys given
in (&& bool (canUnify poly_given_ok) eqType is_first w g)
. flip all (zip ws gs)
$ \(wt, gt) -> canUnify poly_given_ok wt gt || go False wt gt
canUnify :: Bool -> Type -> Type -> Bool
canUnify poly_given_ok wt gt =
or [ isTyVarTy wt
, isTyVarTy gt && poly_given_ok
, eqType wt gt
]
------------------------------------------------------------------------------
-- | Like 'Control.Monad.when', but in the context of an 'Alternative'.
whenA
:: (Monad m, Alternative z)
=> Bool
-> m a
-> m (z a)
whenA False _ = pure empty
whenA True ma = fmap pure ma
mkWanted
:: SolveContext
-> CtLoc
-> Type
-> Type
-> TcPluginM (Maybe ( (OrdType, OrdType) -- the types we want to unify
, Ct -- the constraint
))
mkWanted solve_ctx loc wanted given =
whenA (not (mustUnify solve_ctx) || canUnifyRecursive solve_ctx wanted given) $ do
(ev, _) <- unsafeTcPluginTcM
. runTcSDeriveds
$ newWantedEq loc Nominal wanted given
pure ( (OrdType wanted, OrdType given)
, CNonCanonical ev
)
thd :: (a, b, c) -> c
thd (_, _, c) = c
countLength :: (a -> a -> Bool) -> [a] -> [(a, Int)]
countLength eq as =
let grouped = groupBy eq as
in zipWith (curry $ bimap head length) grouped grouped
------------------------------------------------------------------------------
-- | 'Type's don't have 'Eq' or 'Ord' instances by default, even though there
-- are functions in GHC that implement these operations. This newtype gives us
-- those instances.
newtype OrdType = OrdType
{ getOrdType :: Type
}
instance Eq OrdType where
(==) = eqType `on` getOrdType
instance Ord OrdType where
compare = nonDetCmpType `on` getOrdType
------------------------------------------------------------------------------
-- | The context in which we're attempting to solve a constraint.
data SolveContext
= -- | In the context of a function definition.
FunctionDef
-- | In the context of running an interpreter. The 'Bool' corresponds to
-- whether we are only trying to solve a single 'Member' constraint right
-- now. If so, we *must* produce a unification wanted.
| InterpreterUse Bool
deriving (Eq, Ord, Show)
mustUnify :: SolveContext -> Bool
mustUnify FunctionDef = True
mustUnify (InterpreterUse b) = b
solveFundep
:: (IORef (S.Set (OrdType, OrdType)), Class)
-> [Ct]
-> [Ct]
-> [Ct]
-> TcPluginM TcPluginResult
solveFundep _ _ _ [] = pure $ TcPluginOk [] []
solveFundep (ref, effCls) giv _ want = do
let wantedEffs = allMonadEffectConstraints effCls want
givenEffs = snd <$> allMonadEffectConstraints effCls giv
num_wanteds_by_r = countLength eqType $ fmap (thd . snd) wantedEffs
must_unify r =
let Just num_wanted = find (eqType r . fst) num_wanteds_by_r
in snd num_wanted /= 1
eqs <- forM wantedEffs $ \(loc, e@(_, eff, r)) -> do
case findMatchingEffectIfSingular e givenEffs of
Nothing -> do
case splitAppTys r of
(_, [_, eff', _]) -> mkWanted (InterpreterUse $ must_unify r) loc eff eff'
_ -> pure Nothing
Just eff' -> mkWanted FunctionDef loc eff eff'
already_emitted <- tcPluginIO $ readIORef ref
let new_wanteds = filter (not . flip S.member already_emitted . fst)
$ catMaybes eqs
tcPluginIO $ modifyIORef ref $ S.union $ S.fromList $ fmap fst new_wanteds
pure . TcPluginOk [] $ fmap snd new_wanteds
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