ParsingFractions.hs

{-# LANGUAGE OverloadedStrings #-}

module Text.Fractions where

import Control.Applicative
import Data.Ratio ((%))
import Text.Trifecta

badFraction = "1/0"
alsoBad = "10"
shouldWork = "1/2"
shouldAlsoWork = "2/1"

parseFraction :: Parser Rational
parseFraction = do
    numerator <- decimal
    char '/'
    denominator <- decimal
    return (numerator % denominator)

virtuousFraction :: Parser Rational
virtuousFraction = do
    numerator <- decimal
    char '/'
    denominator <- decimal
    case denominator of 
        0 -> fail "Can't have 0 denominator"
        _ -> return (numerator % denominator)

mysuccesseoffn :: Parser Integer
mysuccesseoffn = do
    i <- integer
    eof
    return i

testVirtuous :: IO ()
testVirtuous = do
    print $ parseString virtuousFraction mempty badFraction
    print $ parseString virtuousFraction mempty alsoBad
    print $ parseString virtuousFraction mempty shouldWork
    print $ parseString virtuousFraction mempty shouldAlsoWork

main :: IO ()
main = do
    print $ parseString parseFraction mempty shouldWork
    print $ parseString parseFraction mempty shouldAlsoWork
    print $ parseString parseFraction mempty alsoBad
    print $ parseString parseFraction mempty badFraction