module Util0Parser where {

import Text.ParserCombinators.Parsec;
import Text.ParserCombinators.Parsec.Expr;
import Token;
import Util0Type;

-- パーサー

parseExpr :: GenParser Char a Expr;
parseExpr = buildExpressionParser table parseFactor <?> "expression";

table :: [[Operator Char a Expr]];
table = [
         [ Infix (do { reservedOp "*"; return Mult }) AssocLeft],
         [ Infix (do { reservedOp "+"; return Add }) AssocLeft]
        ];

parseFactor :: GenParser Char a Expr;
parseFactor = parens parseExpr
              <|> 
              (do { t <- naturalOrFloat;
                    return (case t of { Left i  -> Const (Num (fromInteger i));
                                        Right d -> Const (Num d) }) })
              <?> "simple expression"
;

myParse :: String -> Expr;
myParse str = case
                (parse (do {whiteSpace; s<- parseExpr; eof; return s }) "" str)
              of {
                Left err -> Const (Num (1/0));
                Right x  -> x
              }
;
}