CODEWITHSUNDEEP
haskellcharbooleanhaskell-platform
sambud_Ger
sambud_Ger

Reputation: 21

Haskell: Comparing Characters

I want to create a function consonant which check, whether an char is an consonant(True) or a vowel(False). I try something like this:

consonant :: Char -> Bool
consonant x = if (x == 'a'|'e'|'i'|'o'|'u'|' ') then False else True

But it doesn't work, i think it is just a problem with the Syntax. I hope anyone can help me :) Thanks

Upvotes: 1

Views: 1384

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476699

The expression x == 'a'|'e'|'i'|'o'|'u'|' ' does not make sense, the pipe character (|) is used for guards, or when defining several data constructors for a data type.

Replacing | with (||) :: Bool -> Bool -> Bool will not help either, since 'e' is not a Bool. We can however write several conditions:

consonant :: Char -> Bool
consonant x = not (x == 'a'|| x == 'e'|| x == 'i'|| x =='o'|| x =='u'|| x ==' ')

or we can make use of elem :: (Eq a, Foldable f) => a -> f a -> Bool:

consonant :: Char -> Bool
consonant = not . flip elem "aeiou "

or we can make use of an operator sectioning as @leftroundabout suggests:

consonant :: Char -> Bool
consonant = not . (`elem` "aeiou ")

or do the "flipping" ourselves with a variable:

consonant :: Char -> Bool
consonant x = not (elem x "aeiou ")

Or we can make use notElem :: (Eq a, Foldable f) => a -> f a -> Bool which negates the elem:

consonant :: Char -> Bool
consonant = (`notElem` "aeiou ")

Upvotes: 3

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