OK

1 files changed, 50 insertions, 4 deletions

diff --git a/src/Eval.hs b/src/Eval.hs
index 72c8985..4e73778 100644
--- a/src/Eval.hs
+++ b/src/Eval.hs
@@ -4,22 +4,68 @@ module Eval
 
 import           Control.Exception
 import           Control.Monad.State
+import           Debug.Trace
+import           Parser
 import           System.Console.Haskeline
 import           System.Environment
 import           System.Exit
 import           System.IO
+import           Text.Parsec             hiding ( State
+                                                , try
+                                                )
 
-type Environment = [String]
+type Environment = [(String, Expression)]
+type Program = State Environment
 
-eval :: String -> IO ()
-eval code = putStrLn "ok"
+eval :: [String] -> Environment -> IO Environment
+eval []          env = pure env
+eval (line : ls) env = case parse parseLine "Evaluator" line of
+  Left  err   -> print err >> pure env
+  Right instr -> case instr of
+    Define name exp ->
+      let (res, env') = evalDefine name exp `runState` env
+      in  case res of
+            Left  err -> print err >> eval ls env'
+            Right _   -> eval ls env'
+    Evaluate exp -> putStrLn "ok" >> pure env
+    _            -> eval ls env
+
+evalVar :: String -> Program (Failable Expression)
+evalVar var = state $ \e ->
+  ( case lookup var e of
+    Nothing -> Left $ UndeclaredFunction var
+    Just x  -> Right x
+  , e
+  )
+
+evalApp :: Expression -> Expression -> Program (Failable Expression)
+evalApp f g =
+  evalExp f
+    >>= (\case
+          Left  e  -> pure $ Left e
+          Right f' -> fmap (Application f') <$> evalExp g
+        )
+
+evalExp :: Expression -> Program (Failable Expression)
+evalExp idx@(Bruijn      _  ) = pure $ Right idx
+evalExp (    Variable    var) = evalVar var
+evalExp (    Abstraction exp) = evalExp exp
+evalExp (    Application f g) = evalApp f g
+
+evalDefine :: String -> Expression -> Program (Failable Expression)
+evalDefine name exp =
+  evalExp exp
+    >>= (\case
+          Left  e -> pure $ Left e
+          Right f -> modify ((name, f) :) >> pure (Right f)
+        )
 
 evalFile :: String -> IO ()
 evalFile path = do
   file <- try $ readFile path :: IO (Either IOError String)
   case file of
     Left  exception -> print (exception :: IOError)
-    Right file      -> eval file
+    Right file      -> eval (lines file) [] >> putStrLn "Done"
 
 evalRepl :: String -> Environment -> InputT IO Environment
 evalRepl line env = outputStrLn (show env) >> pure env