Minimal Parsec parser for FASTA sequence data

fasta.hs

import Text.ParserCombinators.Parsec

fasta :: Parser [[String]]
fasta = do a <- many record
           eof
           return a

record :: Parser [String]
record = do a <- header
            b <- dna
            return [a, b]

header :: Parser String 
header = do char '>'
            a <- many anyChar
            newline
            return a

dna :: Parser String
dna = many nucleotide

nucleotide :: Parser Char
nucleotide = do a <- oneOf "ATCGN"
                skipMany newline 
                return a

main :: IO ()
main = do 
  a <- getContents
  case parse fasta "stdin" a of
    Left  error -> putStr "Error: " >> print error
    Right ast   -> print ast