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.