Removing holding onto val in Interface

src/Data/Abstract/Value.hs

@@ -40,7 +40,7 @@ instance (Ord location) => Ord1 (Closure location) where liftCompare = genericLi
 instance (Show location) => Show1 (Closure location) where liftShowsPrec = genericLiftShowsPrec
 
 -- | A program value consisting of the value of the program and it's enviornment of bindings.
-data Interface location term = Interface (Value location term) (Environment location (Value location term))
+newtype Interface location term = Interface (Environment location (Value location term))
   deriving (Eq, Generic1, Ord, Show)
 
 instance (Eq location) => Eq1 (Interface location) where liftEq = genericLiftEq
@@ -116,7 +116,7 @@ class AbstractValue v where
 instance (FreeVariables term, Ord location) => ValueRoots location (Value location term) where
   valueRoots v
     | Just (Closure names body env) <- prj v = envRoots env (foldr Set.delete (freeVariables body) names)
-    | Just (Interface _ env) <- prj v        = envAll env
+    | Just (Interface env) <- prj v          = envAll env
     | otherwise                              = mempty
 
 -- | Construct a 'Value' wrapping the value arguments (if any).

src/Data/Syntax.hs

@@ -160,10 +160,10 @@ instance ( Ord (LocationFor (Value l t))
          => Evaluatable es t (Value l t) Program where
   eval (Program xs) = eval' xs
     where
-      interface val = inj . Value.Interface val <$> ask @(EnvironmentFor (Value l t))
+      interface = inj . Value.Interface <$> ask @(EnvironmentFor (Value l t))
 
-      eval' [] = interface unit
-      eval' [x] = step x >>= interface
+      eval' [] = interface
+      eval' [x] = step @(Value l t) x >> interface
       eval' (x:xs) = do
         _ <- step @(Value l t) x
         env <- get @(EnvironmentFor (Value l t))

src/Data/Syntax/Declaration.hs

@@ -288,11 +288,10 @@ instance ( Show l
          => Evaluatable es t (Value l t) Import where
   eval (Import from _ _) = do
     interface <- require @(Value l t) @t from
-    -- TODO: Consider returning the value instead of the interface.
-    Interface _ env <- maybe
-                           (fail ("expected an interface, but got: " <> show interface))
-                           pure
-                           (prj interface :: Maybe (Value.Interface l t))
+    Interface env <- maybe
+                      (fail ("expected an interface, but got: " <> show interface))
+                      pure
+                      (prj interface :: Maybe (Value.Interface l t))
 
     modify (envUnion env)
     pure interface