Question

I’ve tried to write a function to do this but can’t get GHCI to understand my code. I’m coming from an OOP background so functional programming is completely new territory for me.

checkPigLatin :: String -> String
checkPigLatin sentence (x:xs)
    | check == "true" = "This is Pig Latin"
    | otherwise = "Not Pig Latin"
    where check = if (x `elem` "aeiouAEIOU", '-' `elem` xs, snd(break('a'==) xs) == 'a', snd(break('a'==) xs) == 'y') then "true"

Answer 1

Several issues here:

1. The type of your function is String -> String, so it should only have one argument, while your definition has two arguments, sentence and (x:xs).
2. Don’t use strings like "true" and "false". Use booleans. That’s what they’re for.
3. The condition of an if must be a boolean. If you want several conditions to hold, use (&&) or and to combine them.
4. An if-expression must have both a then and an else. You can think of if x then y else z like the ternary x ? y : z operator in some other languages.
5. 'a' and 'y' have type Char, so you can’t compare them against strings with ==. Compare with "a" and "y" instead.

However, there is no point in writing if something then True else False. Instead, just use the boolean expression directly.

checkPigLatin :: String -> String
checkPigLatin (x:xs)
    | check     = "This is Pig Latin"
    | otherwise = "Not Pig Latin"
    where check = and [ x `elem` "aeiouAEIOU"
                      , '-' `elem` xs
                      , snd (break ('a'==) xs) == "a"
                      , snd (break ('a'==) xs) == "y"
                      ]