takeWhile is an Attoparsec combinator that reads consecutive input bytes or characters while a predicate remains true, returning the consumed input. The parser stops before the first character that fails the predicate. section 12.2.1
Use the variant that matches the input and predicate:
- Data.Attoparsec.ByteString.takeWhile :: (Word8 -> Bool) -> Parser ByteString reads bytes. section 12.2.1
- Data.Attoparsec.ByteString.Char8.takeWhile works with Char predicates, which is convenient for ASCII-oriented parsing. section 12.2.1
- Unlike skipWhile, takeWhile preserves the matching input as a ByteString. section 12.2.1
Reading a PNM comment
A PNM comment begins with '%' and continues until a newline. Combine char with takeWhile to consume its body: comment :: Parser BS.ByteString; comment = C8.char '%' >> C8.takeWhile (/= '\n'). This parser consumes the percent sign and all non-newline characters, leaving the newline for subsequent parsing. section 12.2.2
Listing 12.21 A parser for comments
comment :: Parser BS.ByteString comment = C8.char '%' >> C8.takeWhile (/= '\n') #1
View the complete comment parser used for PNM header parsing. section 12.2.2
