lex.hs

import           Control.Monad
import           System.IO
import           Text.ParserCombinators.Parsec
import           Text.ParserCombinators.Parsec.Expr
import           Text.ParserCombinators.Parsec.Language
import qualified Text.ParserCombinators.Parsec.Token    as Token

languageDef =
    emptyDef
    { Token.commentLine = "%"
    , Token.identStart = letter
    , Token.identLetter = alphaNum
    , Token.reservedNames =
          ["\\", "$", "\\(", "\\)", "\\[", "\\]", "$$", "{", "}"]
    , Token.reservedOpNames = ["\\", "$", "\\(", "\\)", "\\[", "\\]", "$$"]
    }

lexer = Token.makeTokenParser languageDef


parseString :: String -> Stmt
parseString str =
   case parse whileParser "" str of
     Left e  -> error $ show e
     Right r -> r

parseFile :: String -> IO Stmt
parseFile file = do
    program  <- readFile file
  case parse whileParser "" program of
        Left e  -> print e >> fail "parse error"
        Right r -> return r


main :: IO ()
main = do
    error "undefined: `main' in lex.hs"