plugin

polysemy-plugin/.gitignore

@@ -0,0 +1,3 @@
+.stack-work/
+polysemy-plugin.cabal
+*~

polysemy-plugin/ChangeLog.md

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+# Changelog for polysemy-plugin
+
+## Unreleased changes

polysemy-plugin/LICENSE

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+Copyright Sandy Maguire (c) 2019
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Sandy Maguire nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

polysemy-plugin/README.md

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+# polysemy-plugin

polysemy-plugin/Setup.hs

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+import Distribution.Simple
+main = defaultMain

polysemy-plugin/package.yaml

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+name:                polysemy-plugin
+version:             0.1.0.0
+github:              "isovector/polysemy-plugin"
+license:             BSD3
+author:              "Sandy Maguire"
+maintainer:          "sandy@sandymaguire.me"
+copyright:           "2019 Sandy Maguire"
+
+extra-source-files:
+- README.md
+- ChangeLog.md
+
+# Metadata used when publishing your package
+# synopsis:            Short description of your package
+# category:            Web
+
+# To avoid duplicated efforts in documentation and dealing with the
+# complications of embedding Haddock markup inside cabal files, it is
+# common to point users to the README.md file.
+description:         Please see the README on GitHub at <https://github.com/isovector/polysemy-plugin#readme>
+
+dependencies:
+- base >= 4.7 && < 5
+- ghc
+- ghc-tcplugins-extra
+- polysemy
+
+library:
+  source-dirs: src
+
+tests:
+  polysemy-plugin-test:
+    main:                Spec.hs
+    source-dirs:         test
+    ghc-options:
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N
+    dependencies:
+    - polysemy-plugin

polysemy-plugin/src/Polysemy/Plugin.hs

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+{-# LANGUAGE NoMonomorphismRestriction #-}
+{-# LANGUAGE CPP #-}
+
+module Polysemy.Plugin
+  ( plugin
+  ) where
+
+-- external
+import GHC.TcPluginM.Extra (lookupModule, lookupName)
+
+-- GHC API
+import FastString (fsLit)
+import Module     (mkModuleName)
+import OccName    (mkTcOcc)
+import Plugins    (Plugin (..), defaultPlugin
+#if __GLASGOW_HASKELL__ >= 806
+    , PluginRecompile(..)
+#endif
+    )
+import TcPluginM  (TcPluginM, tcLookupClass)
+import TcRnTypes
+import TyCoRep    (Type (..))
+import Control.Monad
+import Class
+import Type
+import Data.Maybe
+import TcSMonad hiding (tcLookupClass)
+import CoAxiom
+import Outputable
+
+plugin :: Plugin
+plugin = defaultPlugin
+    { tcPlugin = const (Just fundepPlugin)
+#if __GLASGOW_HASKELL__ >= 806
+    , pluginRecompile = const (return NoForceRecompile)
+#endif
+    }
+
+fundepPlugin :: TcPlugin
+fundepPlugin = TcPlugin
+    { tcPluginInit = do
+        md <- lookupModule (mkModuleName "Polysemy") (fsLit "polysemy")
+        monadEffectTcNm <- lookupName md (mkTcOcc "Member")
+        tcLookupClass monadEffectTcNm
+    , tcPluginSolve = solveFundep
+    , tcPluginStop = const (return ()) }
+
+allMonadEffectConstraints :: Class -> [Ct] -> [(CtLoc, (Type, Type, Type))]
+allMonadEffectConstraints cls cts =
+    [ (ctLoc cd, (effName, eff, mon))
+        | cd@CDictCan{cc_class = cls', cc_tyargs = [eff, mon]} <- cts
+        , cls == cls'
+        , let (effName, _) = splitAppTys 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' ]
+
+solveFundep :: Class -> [Ct] -> [Ct] -> [Ct] -> TcPluginM TcPluginResult
+solveFundep effCls giv _ want = do
+    pprPanic "wat" $ ppr $ giv ++ want
+    let wantedEffs = allMonadEffectConstraints effCls want
+    let givenEffs = snd <$> allMonadEffectConstraints effCls giv
+    eqs <- forM wantedEffs $ \(loc, e@(_, eff, _)) ->
+        case findMatchingEffectIfSingular e givenEffs of
+            Nothing -> return Nothing
+            Just eff' -> do
+                (ev, _) <- unsafeTcPluginTcM
+                    (runTcSDeriveds (newWantedEq loc Nominal eff eff'))
+                return (Just (CNonCanonical ev))
+    return (TcPluginOk [] (catMaybes eqs))
+

polysemy-plugin/test/Spec.hs

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+main :: IO ()
+main = putStrLn "Test suite not yet implemented"

stack.yaml

@@ -2,6 +2,7 @@ resolver: lts-13.0
 
 packages:
 - .
+- polysemy-plugin
 
 extra-deps:
 - dump-core-0.1.3.2