module Var where {

import VarType;
import VarParser;

{----------------------------------------------------------------------

インタプリタその1

* Util0 + 
* 変数宣言

 Expr -> Expr * Expr 
       | Expr + Expr 
       | Const
       | ( Expr )
       | Ident
       | let Ident = Expr in Expr

       
 ----------------------------------------------------------------------}

{-
 -- Monadic Version

interp :: Expr -> Env -> M Value;
interp (Const c) e      = unitM c;
interp (Add m n) e      = interp m e `bindM` \ (Num c) ->
                          interp n e `bindM` \ (Num d) ->
                          unitM (Num (c+d));
interp (Mult m n) e     = interp m e `bindM` \ (Num c) ->
                          interp n e `bindM` \ (Num d) ->
                          unitM (Num (c*d));
interp (Var x) e        = unitM (lookupEnv e x);
interp (Let (x, m) n) e = interp m e `bindM` \ v  -> 
                          interp n ((x,v):e);
-}

type Env = [(String, Value)];

-- lookup' :: Eq a =>  a -> [(a, b)] -> b;
lookup' :: String -> [(String, a)] -> a;
lookup' x ((n,v):rest) = if n==x then v else lookup' x rest;

 -- Non-Monadic Version 
interp :: Expr -> Env -> Value;
interp (Const c) e      = c;
interp (Add m n) e      = let { 
                            Num c = interp m e;
                            Num d = interp n e 
                          } in 
                          Num (c+d);
interp (Mult m n) e     = let { 
                            Num c = interp m e;
                            Num d = interp n e 
                          } in 
                          Num (c*d);
interp (Var x) e        = lookup' x e;
interp (Let (x, m) n) e = let { v = interp m e } in
                          interp n ((x,v):e);


run :: String -> String;
run str = showValue (interp (myParse str) []);

main :: IO ();
main = interact run;

load :: String -> IO ();
load path = readFile path >>= \ prog ->
            putStrLn (run prog);

-- for example
-- run "let x=2*2 in let y=x*x in y*y"
}