From 2df600835fc95e9a9ce947cdbac202c553ad13da Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@me.com>
Date: Thu, 30 Nov 2017 17:43:30 -0500
Subject: [PATCH] Move MonadGC into its own module.

---
 semantic-diff.cabal            |  1 +
 src/Abstract/Eval.hs           | 17 +----------------
 src/Control/Monad/Effect/GC.hs | 19 +++++++++++++++++++
 3 files changed, 21 insertions(+), 16 deletions(-)
 create mode 100644 src/Control/Monad/Effect/GC.hs

diff --git a/semantic-diff.cabal b/semantic-diff.cabal
index 285d0d30b..22e556924 100644
--- a/semantic-diff.cabal
+++ b/semantic-diff.cabal
@@ -39,6 +39,7 @@ library
                      , Control.Effect
                      , Control.Monad.Effect.Env
                      , Control.Monad.Effect.Fresh
+                     , Control.Monad.Effect.GC
                      -- General datatype definitions & generic algorithms
                      , Data.Algebra
                      , Data.Align.Generic
diff --git a/src/Abstract/Eval.hs b/src/Abstract/Eval.hs
index 19105071a..06fd64b8f 100644
--- a/src/Abstract/Eval.hs
+++ b/src/Abstract/Eval.hs
@@ -7,16 +7,12 @@ module Abstract.Eval
 
 import Abstract.Environment
 import Abstract.FreeVariables
-import Abstract.Store
 import Abstract.Value
-import Control.Monad.Effect
 import Control.Monad.Effect.Env
-import Control.Monad.Effect.Reader
+import Control.Monad.Effect.GC
 import Control.Monad.Fail
 import Data.Functor.Classes
 import Data.Proxy
-import Data.Semigroup
-import qualified Data.Set as Set
 import Data.Term
 import Data.Union
 import Prelude hiding (fail)
@@ -35,17 +31,6 @@ instance (Monad m, Eval t v m s) => Eval t v m (TermF s a) where
   eval ev yield In{..} = eval ev yield termFOut
 
 
-class Monad m => MonadGC a m where
-  askRoots :: m (Set.Set (Address (LocationFor a) a))
-
-  extraRoots :: Set.Set (Address (LocationFor a) a) -> m b -> m b
-
-instance (Ord (LocationFor a), Reader (Set.Set (Address (LocationFor a) a)) :< fs) => MonadGC a (Eff fs) where
-  askRoots = ask :: Eff fs (Set.Set (Address (LocationFor a) a))
-
-  extraRoots roots' = local (<> roots')
-
-
 instance ( Monad m
          , Ord (LocationFor v)
          , MonadGC v m
diff --git a/src/Control/Monad/Effect/GC.hs b/src/Control/Monad/Effect/GC.hs
new file mode 100644
index 000000000..31fd46b0a
--- /dev/null
+++ b/src/Control/Monad/Effect/GC.hs
@@ -0,0 +1,19 @@
+{-# LANGUAGE MultiParamTypeClasses, ScopedTypeVariables, TypeOperators, UndecidableInstances #-}
+module Control.Monad.Effect.GC where
+
+import Abstract.Address
+import Abstract.Value
+import Control.Monad.Effect
+import Control.Monad.Effect.Reader
+import Data.Semigroup ((<>))
+import Data.Set (Set)
+
+class Monad m => MonadGC a m where
+  askRoots :: m (Set (Address (LocationFor a) a))
+
+  extraRoots :: Set (Address (LocationFor a) a) -> m b -> m b
+
+instance (Ord (LocationFor a), Reader (Set (Address (LocationFor a) a)) :< fs) => MonadGC a (Eff fs) where
+  askRoots = ask :: Eff fs (Set (Address (LocationFor a) a))
+
+  extraRoots roots' = local (<> roots')