Capitalize the first letter, all API calls model the possibility of things going wrong, but not with exceptions but with explicit types

CapFirst.elm

-- From https://github.com/dhinojosa/elm-study/blob/master/src/PigLatin.elm

capFirst : String -> String
capFirst s =
    case uncons s of
        Just ( h, t ) ->
            cons (Char.toUpper h) t

        Nothing ->
            ""