Hello all, I am trying to write a small calculator using Parsec. Every thing went fine and I wrote this [1] and now I am trying to use ByteString to make it more faster but getting compiler error which I am not able to figure out. Could some one please tell me what is wrong with this code. In case of indentation error, code on hpaste[2] {-# LANGUAGE OverloadedStrings #-} import qualified Text.Parsec.Token as Token import Text.Parsec.Prim import Text.Parsec.Char import Text.Parsec.Expr import Text.Parsec.Combinator import Text.Parsec.Language import qualified Text.Parsec.ByteString.Lazy as T import qualified Data.ByteString.Lazy.Char8 as BS import Control.Applicative hiding ( ( <|> ) , many ) import Data.Maybe ( fromJust ) languageDef = emptyDef { Token.commentStart = "/*" , Token.commentEnd = "*/" , Token.commentLine = "//" , Token.nestedComments = False , Token.identStart = letter <|> char '_' , Token.identLetter = alphaNum <|> oneOf "_'" , Token.opStart = Token.opLetter emptyDef , Token.opLetter = oneOf ":!#$%&*+./<=>?@\\^|-~" , Token.reservedOpNames= ["*" , "/" , "^" , "+" , "-" ] , Token.reservedNames = [] , Token.caseSensitive = True } lexer = Token.makeTokenParser languageDef identifier = Token.identifier lexer reserved = Token.reserved lexer operator = Token.operator lexer reservedOp = Token.reservedOp lexer natural = Token.natural lexer integer = Token.integer lexer float = Token.float lexer lexeme = Token.lexeme lexer parens = Token.parens lexer whiteSpace = Token.whiteSpace lexer semi = Token.semi lexer comma = Token.comma lexer colon = Token.colon lexer dot = Token.dot lexer semiSep = Token.semiSep lexer commaSep = Token.commaSep lexer data Expr = Num Integer | Add Expr Expr | Sub Expr Expr | Mul Expr Expr | Div Expr Expr | Exp Expr Expr deriving Show exprCal :: T.Parser Expr exprCal = buildExpressionParser table factor table = [ [ op "^" Exp AssocRight ] , [ op "*" Mul AssocLeft, op "/" Div AssocLeft ] , [ op "+" Add AssocLeft, op "-" Sub AssocLeft ] ] where op s f assoc = Infix ( reservedOp s >> return f ) assoc factor :: T.Parser Expr factor = parens exprCal <|> Num <$> integer calExpression :: Expr -> Integer calExpression ( Num n ) = n calExpression ( Add e1 e2 ) = calExpression e1 + calExpression e2 calExpression ( Sub e1 e2 ) = calExpression e1 - calExpression e2 calExpression ( Mul e1 e2 ) = calExpression e1 * calExpression e2 calExpression ( Div e1 e2 ) = div ( calExpression e1 ) ( calExpression e2 ) calExpression ( Exp e1 e2 ) = calExpression e1 ^ ( calExpression e2 ) calculator :: String -> Integer calculator expr = case parse ( whiteSpace >> exprCal ) "" ( BS.pack expr ) of Left msg -> error "failed to parse" Right ( val ) -> calExpression val *Main> :load "/Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs" [1 of 1] Compiling Main ( /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs, interpreted ) /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs:56:36: Couldn't match type `[Char]' with `BS.ByteString' Expected type: OperatorTable BS.ByteString () Data.Functor.Identity.Identity Expr Actual type: [[Operator String () Data.Functor.Identity.Identity Expr]] In the first argument of `buildExpressionParser', namely `table' In the expression: buildExpressionParser table factor In an equation for `exprCal': exprCal = buildExpressionParser table factor /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs:67:11: Couldn't match type `[Char]' with `BS.ByteString' Expected type: ParsecT BS.ByteString () Data.Functor.Identity.Identity Expr Actual type: ParsecT String () Data.Functor.Identity.Identity Expr In the return type of a call of `parens' In the first argument of `(<|>)', namely `parens exprCal' In the expression: parens exprCal <|> Num <$> integer /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs:67:19: Couldn't match type `BS.ByteString' with `[Char]' Expected type: ParsecT String () Data.Functor.Identity.Identity Expr Actual type: T.Parser Expr In the first argument of `parens', namely `exprCal' In the first argument of `(<|>)', namely `parens exprCal' In the expression: parens exprCal <|> Num <$> integer /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs:68:21: Couldn't match type `[Char]' with `BS.ByteString' Expected type: ParsecT BS.ByteString () Data.Functor.Identity.Identity Integer Actual type: ParsecT String () Data.Functor.Identity.Identity Integer In the second argument of `(<$>)', namely `integer' In the second argument of `(<|>)', namely `Num <$> integer' In the expression: parens exprCal <|> Num <$> integer /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs:82:46: Couldn't match type `BS.ByteString' with `[Char]' Expected type: ParsecT String () Data.Functor.Identity.Identity Expr Actual type: T.Parser Expr In the second argument of `(>>)', namely `exprCal' In the first argument of `parse', namely `(whiteSpace >> exprCal)' In the expression: parse (whiteSpace >> exprCal) "" (BS.pack expr) /Users/mukeshtiwari/Programming/Code/Compilers/ParsecExample.hs:82:62: Couldn't match type `BS.ByteString' with `[Char]' Expected type: String Actual type: BS.ByteString In the return type of a call of `BS.pack' In the third argument of `parse', namely `(BS.pack expr)' In the expression: parse (whiteSpace >> exprCal) "" (BS.pack expr) Failed, modules loaded: none. Prelude> Mukesh Tiwari [1] http://hpaste.org/88155 [2] http://hpaste.org/88156