1 files changed, 31 insertions, 24 deletions

diff --git a/lib/Language/Elna/SymbolTable.hs b/lib/Language/Elna/SymbolTable.hs
index c8406fc..52b8542 100644
--- a/lib/Language/Elna/SymbolTable.hs
+++ b/lib/Language/Elna/SymbolTable.hs
@@ -1,64 +1,72 @@
 module Language.Elna.SymbolTable
     ( SymbolTable
-    , empty
-    {-, Info(..)
+    , Info(..)
     , ParameterInfo(..)
     , builtInSymbolTable
+    , empty
     , enter
     , fromList
     , lookup
-    , member -}
+    , member
+    , scope
+    , toMap
+    , update
     ) where
 
-data SymbolTable = SymbolTable -- (HashMap Identifier Info)
-    deriving (Eq, Show)
-
-empty :: SymbolTable
-empty = SymbolTable -- HashMap.empty
-
-{-
 import Data.HashMap.Strict (HashMap)
 import qualified Data.HashMap.Strict as HashMap
 import Data.List (sort)
 import Data.List.NonEmpty (NonEmpty)
 import qualified Data.List.NonEmpty as NonEmpty
+import Data.Maybe (isJust)
 import Data.Vector (Vector)
 import Language.Elna.Location (Identifier(..))
 import Language.Elna.Types (Type(..), intType, booleanType)
 import Prelude hiding (lookup)
 
-instance Semigroup SymbolTable
-  where
-    (SymbolTable lhs) <> (SymbolTable rhs) = SymbolTable $ rhs <> lhs
+data SymbolTable = SymbolTable (Maybe SymbolTable) (HashMap Identifier Info)
+    deriving (Eq, Show)
 
-instance Monoid SymbolTable
-  where
-    mempty = empty
+empty :: SymbolTable
+empty = SymbolTable Nothing HashMap.empty
+
+update :: (Info -> Maybe Info) -> Identifier -> SymbolTable -> SymbolTable
+update updater key (SymbolTable parent mappings) = SymbolTable parent
+    $ HashMap.update updater key mappings
+
+scope :: SymbolTable -> SymbolTable -> SymbolTable
+scope parent (SymbolTable _ mappings) = SymbolTable (Just parent) mappings
 
 builtInSymbolTable :: SymbolTable
-builtInSymbolTable = SymbolTable $ HashMap.fromList
+builtInSymbolTable = SymbolTable Nothing $ HashMap.fromList
     [ ("boolean", TypeInfo booleanType)
     , ("int", TypeInfo intType)
     ]
 
+toMap :: SymbolTable  -> HashMap Identifier Info
+toMap (SymbolTable _ map') = map'
+
 enter :: Identifier -> Info -> SymbolTable -> Maybe SymbolTable
-enter identifier info table@(SymbolTable hashTable)
+enter identifier info table@(SymbolTable parent hashTable)
     | member identifier table = Nothing
     | otherwise = Just
-        $ SymbolTable
-        $ HashMap.insert identifier info hashTable
+        $ SymbolTable parent (HashMap.insert identifier info hashTable)
 
 lookup :: Identifier -> SymbolTable -> Maybe Info
-lookup identifier (SymbolTable table) = HashMap.lookup identifier table
+lookup identifier (SymbolTable parent table)
+    | Just found <- HashMap.lookup identifier table = Just found
+    | Just parent' <- parent = lookup identifier parent'
+    | otherwise = Nothing
 
 member :: Identifier -> SymbolTable -> Bool
-member identifier (SymbolTable table) = HashMap.member identifier table
+member identifier table =
+    isJust $ lookup identifier table
 
 fromList :: [(Identifier, Info)] -> Either (NonEmpty Identifier) SymbolTable
 fromList elements
     | Just identifierDuplicates' <- identifierDuplicates =
         Left identifierDuplicates'
-    | otherwise = Right $ SymbolTable $ HashMap.fromList elements
+    | otherwise = Right $ SymbolTable Nothing $ HashMap.fromList elements
   where
     identifierDuplicates = NonEmpty.nonEmpty
         $ fmap NonEmpty.head
@@ -77,4 +85,3 @@ data Info
     | VariableInfo Bool Type
     | ProcedureInfo SymbolTable (Vector ParameterInfo)
     deriving (Eq, Show)
--}