On Saturday 02 February 2013, 15:00:52, Kees Bleijenberg wrote:

module Main(main) where

import Text.ParserCombinators.Parsec

parseToNewLine = do line <- manyTill anyChar newline return line

keyValue = do fieldName <- many letter spaces char '=' spaces fieldValue <- parseToNewLine return (fieldName,fieldValue)

main = parseTest keyValue "key=\n"

I don’t understand why te code above doesn’t parse to (“key”,””)

Because the newline is already consumed by the `spaces`. So parseToNewLine gets an empty string as input, and fails on that.

parseToNewLine “\n” parses to “"

parseTest keyValue “a=b\n” works fine and parses to (“a”,”b”)

The input of parseToNewLine must contain a newline, or it fails. In the last example, the `spaces` after `char '='` stops at reaching the 'b', so the newline remains. In the first (problematic) example, all the remaining input after the '=' consists of whitespace.