Sexp parser example

Lib.hs

{-# LANGUAGE DataKinds #-}

module Lib
       ( primitiveRead
       , LispType ( Nil
                  , LispInteger
                  , LispString
                  , LispSymbol
                  , LispTrue
                  , LispList )
       ) where

import Text.Parsec
import Data.Text (Text)
import qualified Data.Text as Text

data LispType = Nil
              | LispInteger Integer
              | LispString Text
              | LispSymbol Text
              | LispTrue
              | LispList [LispType]
              deriving (Show)

primitiveRead :: String -> Text -> Either ParseError LispType
primitiveRead source text = runParser lispParser () source text

type LispParser a = Parsec Text () a

whitespace :: LispParser ()
whitespace = skipMany space

nilParser :: LispParser LispType
nilParser = string "NIL" >> return Nil

trueParser :: LispParser LispType
trueParser = string "T" >> return LispTrue

symbolParser :: LispParser LispType
symbolParser = LispSymbol . Text.pack <$> many1 (choice [alphaNum, oneOf "!$%&*+-./:<=>?@^_~"])

integerParser :: LispParser LispType
integerParser = LispInteger . (read :: String -> Integer) <$> many1 digit

stringParser :: LispParser LispType
stringParser =  LispString . Text.pack <$> between (char '"') (char '"') (many (noneOf ['"']))

listParser :: LispParser LispType
listParser = LispList <$> between (char '(') (char ')') (many1 lispParser)

lispParser :: LispParser LispType
lispParser = whitespace
             >> choice [ nilParser
                       , trueParser
                       , integerParser
                       , stringParser
                       , symbolParser
                       , listParser ]