構文解析 48時間でSchemeを書こう

• Ubuntu用のlibghc-parsec-devをインストール

sudo apt-get install libghc-parsec3-dev

• テキストに沿ってファイル file2.hs を作ってコンパイルする

import Text.ParserCombinators.Parsec hiding (spaces)
import System.Environment
import System.IO
import Control.Monad

{-
シンボルを認識させる
-}
symbol :: Parser Char
symbol = oneOf "!#$%&|*+-/:<=>?@^_~"

{-
空白は無視
-}
spaces :: Parser ()
spaces = skipMany1 space

data LispVal = Atom String
             | List [LispVal]
             | DottedList [LispVal] LispVal
             | Number Integer
             | String String
             | Bool Bool

parseString :: Parser LispVal
parseString = do char '"'
                 x <- many (noneOf "\"")
                 char '"'
                 return $ String x

parseAtom :: Parser LispVal
parseAtom = do first <- letter <|> symbol
               rest <- many (letter <|> digit <|> symbol)
               let atom = first:rest
               return $ case atom of
                          "#t" -> Bool True
                          "#f" -> Bool False
                          _    -> Atom atom

parseNumber :: Parser LispVal
parseNumber = liftM (Number . read) $ many1 digit

parseExpr :: Parser LispVal
parseExpr = parseAtom
        <|> parseString
        <|> parseNumber

readExpr :: String -> String
readExpr input = case parse parseExpr "lisp" input of
    Left err -> "No match: " ++ show err
    Right _ -> "Found value"

{-                                                       
readExpr input = case parse (spaces >> symbol) "lisp" input of
    Left err -> "No match: " ++ show err
    Right val -> "Found value"
-}



main :: IO ()
main = do args <- getArgs
          putStrLn (readExpr (args !! 0))

ghc -package parsec -o simple_parser --make file2.hs
./simple_parser hoge