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module Fractran.Parser (
FractranProgram(..),
parseFractran
) where
import Control.Applicative( some )
import Text.ParserCombinators.Parsec
data FractranProgram = FractranProgram { fractions :: [(Int,Int)]
, initialValue :: Int }
deriving (Show, Eq)
parseFractran :: String -> Either ParseError FractranProgram
parseFractran = parse fractran "error"
fractran = do
whiteSpace
value <- initVal
fractionList <- many intPair
eof
return (FractranProgram fractionList value)
intPair = do
numerator <- wholeNumber
slash
denominator <- positiveNumber
whiteSpace
return (numerator,denominator)
slash = char '/'
<?> "slash character"
initVal = do
value <- wholeNumber
whiteSpace
return value
wholeNumber = do
value <- some digit
return (read value)
positiveNumber = do
firstDigit <- nonZeroDigit
rest <- many digit
return (read (firstDigit:rest))
nonZeroDigit = oneOf "123456789"
<?> "non-zero digit"
whiteSpace = many (oneOf "\t\n\r ")
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