Simple Haskell program to check if the input (command-line arguments) form a pangram, containing all 26 letters of the English alphabet

pangram.hs

import Data.Char (toUpper)
import Data.List (intercalate)
import Data.List.NonEmpty (NonEmpty, nonEmpty, toList)
import System.Environment (getArgs)

data PangramResult = Pangram | MissingLetters (NonEmpty Char)

checkPangram :: String -> PangramResult
checkPangram s = case nonEmpty missingLetters of
    Just ls -> MissingLetters ls
    Nothing -> Pangram
    where
        missingLetters = filter (not . (`elem` normalized)) ['A'..'Z']
        normalized = map toUpper s

getText :: IO String
getText = concat <$> getArgs

showLetters :: NonEmpty Char -> String
showLetters = intercalate ", " . map (:[]) . toList

main = do
    text <- getText
    let
        message = case checkPangram text of
            Pangram -> "Pangram"
            MissingLetters ls -> "Not a pangram: Missing " ++ showLetters ls
    putStrLn message

@ObjectBoxPC I'm glad it was helpful. I definitely relate to the tendency to want to write your main as a pipeline, so I tend to favor the putStrLn . msg . concat =<< getArgs style. It never bothered me that the entrance to the pipeline is on the right side, because that's how function application is written in every programming language and traditionally on paper.