More Monte Monad.

Main.hs

@@ -300,19 +300,6 @@ import Masque.Vats
 --     ej@(EjectorObj u) <- newEjector
 --     catchEjector u $ action ej
 -- 
--- getNames :: Monte (S.Set String)
--- getNames = do
---     env <- view id
---     envs <- use envStack
---     return $ S.unions (map (M.keysSet . _unEnv) (env : NE.toList envs))
--- 
--- getBinding :: String -> Monte Binding
--- getBinding name = do
---     names <- getNames
---     binding <- preuse $ envStack . traverse . unEnv . ix name
---     let availableNames = S.unions [S.fromList builtins, names]
---     maybe (left $ BadName name availableNames) return binding
--- 
 -- bindToObj :: Binding -> Monte Obj
 -- bindToObj (DefBind o) = return o
 -- bindToObj (VarBind ref _) = liftIO $ readIORef ref

Masque/Monte.hs

@@ -5,6 +5,7 @@ module Masque.Monte where
 import Control.Lens
 import Control.Monad.Trans.Either
 import Control.Monad.Trans.State
+import Data.Foldable (toList)
 import Data.List.NonEmpty (NonEmpty(..))
 import qualified Data.Map as M
 import qualified Data.Set as S
@@ -76,3 +77,23 @@ unwrapInt _ = left WrongType
 unwrapStr :: Obj -> Monte String
 unwrapStr (StrObj s) = return s
 unwrapStr _ = left WrongType
+
+namesInScope :: Monte (S.Set String)
+namesInScope = do
+    envs <- use envStack
+    return $ S.unions (map (M.keysSet . _unEnv) (toList envs))
+
+-- | Lookup a name in the current scope.
+maybeLookupName :: String -> Monte (Maybe Binding)
+maybeLookupName name = preuse $ envStack . traverse . unEnv . ix name
+
+-- | Lookup a name in the current scope. If not found, transition to an
+--   erroring state with a helpful error message.
+lookupName :: String -> Monte Binding
+lookupName name = do
+    maybeBinding <- maybeLookupName name
+    case maybeBinding of
+        Just binding -> return binding
+        Nothing -> do
+            names <- namesInScope
+            left $ BadName name names

Masque/Objects.hs

@@ -1,5 +1,8 @@
+{-# LANGUAGE TemplateHaskell #-}
+
 module Masque.Objects where
 
+import Control.Lens
 import Data.Foldable (toList)
 import Data.IORef
 import Data.List
@@ -48,3 +51,5 @@ instance Show Binding where
 
 newtype Env = Env { _unEnv :: M.Map String Binding }
     deriving (Show)
+
+makeLenses ''Env