On Sun, 2009-12-27 at 02:18 -0800, CK Kashyap wrote:
Hi All, I recently came across the paper titled "Monadic Parser Combinators" - After going through it a few times, I think I am beginning to understand monads. However, the parser developed in the paper does not generate an AST - I feel, I'd grasp the whole thing a lot better if I could go over a sample that generates an AST from a simple expression (or even a standard language such as C or Java) ... Can someone please point me to a sample that generates AST - preferably with the simple parser combinator given in the paper. Regards, Kashyap
It parses something like "x+y+z*pi" import Control.Applicative import Text.ParserCombinators.Parsec hiding ((<|>)) data Expr = Variable String | Add Expr Expr | Mul Expr Expr deriving (Show) parseAST :: Parser Expr parseAST = parseAdd parseAdd :: Parser Expr parseAdd = parseMul >>= \e -> ((string "+" >> (Add e <$> parseAdd)) <|> (return e)) parseMul :: Parser Expr parseMul = parseBase >>= \e -> ((string "*" >> (Mul e <$> parseMul)) <|> (return e)) parseBase :: Parser Expr parseBase = (string "(" *> parseAST <* string ")") <|> (Variable <$> many1 letter) Regards