module Util0 where {

import Util0Type;
import Util0Parser;

{----------------------------------------------------------------------
インタプリタその0

* 基本形

 Expr -> Expr * Expr
       | Expr + Expr 
       | Const
       | ( Expr )
 ----------------------------------------------------------------------}

interp :: Expr -> Value;
interp (Const c)  = c;
interp (Add m n)  = let { 
                      Num c = interp m;
                      Num d = interp n 
                    } in 
                    Num (c+d);
interp (Mult m n) = let { 
                      Num c = interp m;
                      Num d = interp n 
                    } in 
                    Num (c*d);

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);
}