Solving Counting DNA Nucleotides on Project Rosalind

CountingDNANucleotides2.hs

import Data.Char
import Data.List

data DNANucleotide = A | C | G | T deriving(Show, Eq, Ord, Read)

charToDNANucleotide :: Char -> DNANucleotide
charToDNANucleotide c = read [toUpper c] :: DNANucleotide

mainCountDNANucleotides = do
  dna <- getLine
  putStrLn $ unwords . map show . map length . group . sort $ map charToDNANucleotide dna