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|
{-# LANGUAGE RecordWildCards #-}
module ArgsPlugin where
-- base
import Data.Maybe
( catMaybes )
-- ghc
import GHC.Builtin.Types
( integerTy )
import GHC.Core
( Expr(Type) )
import GHC.Core.Class
( Class(..) )
import GHC.Core.DataCon
( classDataCon )
import GHC.Core.Make
( mkCoreConApps, mkIntegerExpr )
import GHC.Core.Type
( eqType )
import GHC.Plugins
( Plugin )
import GHC.Tc.Plugin
( TcPluginM, getTargetPlatform )
import GHC.Tc.Types
( TcPluginSolveResult(..) )
import GHC.Tc.Types.Constraint
( Ct(..) )
import GHC.Tc.Types.Evidence
( EvBindsVar, EvTerm(EvExpr) )
import GHC.Platform
( Platform )
-- common
import Common
( PluginDefs(..)
, mkPlugin, don'tRewrite
)
--------------------------------------------------------------------------------
-- This plugin solves Wanted constraints of the form "MyClass Integer",
-- and supplies evidence that depends on the arguments to the plugin.
--
-- To find such constraints, we traverse through the Wanteds provided
-- to the plugin to find those whose name matches that of "MyClass",
-- and check that it is applied to the type "Integer".
--
-- We then construct a dictionary which is the integer that was passed
-- as an argument to the plugin.
plugin :: Plugin
plugin = mkPlugin solver don'tRewrite
-- Solve "MyClass Integer" with a class dictionary that depends on
-- a plugin argument.
solver :: [String]
-> PluginDefs -> EvBindsVar -> [Ct] -> [Ct]
-> TcPluginM TcPluginSolveResult
solver args defs _ev _gs ws = do
let
argsVal :: Integer
argsVal = case args of
arg : _ -> read arg
_ -> error "ArgsPlugin: expected at least one argument"
platform <- getTargetPlatform
solved <- catMaybes <$> traverse ( solveCt platform defs argsVal ) ws
pure $ TcPluginOk solved []
solveCt :: Platform -> PluginDefs -> Integer -> Ct -> TcPluginM ( Maybe (EvTerm, Ct) )
solveCt platform ( PluginDefs {..} ) i ct@( CDictCan { cc_class, cc_tyargs } )
| className cc_class == className myClass
, [tyArg] <- cc_tyargs
, tyArg `eqType` integerTy
, let
evTerm :: EvTerm
evTerm = EvExpr $
mkCoreConApps ( classDataCon cc_class )
[ Type integerTy, mkIntegerExpr platform i ]
= pure $ Just ( evTerm, ct )
solveCt _ _ _ ct = pure Nothing
|
