[Haskell-beginners] May I ask what is the meaning of ch <= 'z' and 'a' <= ch.

[Francesco Ariis]

On Tue, Apr 10, 2018 at 08:47:17PM +0800, 清羽 wrote:
>     And May I ask what is the meaning of ch <= 'z' and 'a' <= ch? I copied this as a condition and solved the problem.here is my work.
>     isLower :: Char -> Bool
>     isLower x = if x ch <= 'z' && 'a' <= ch then True else False.
>     Thanks in advance.

Hello 清羽, Char is an instance of Ord, so you can use <, compare, etc.
with it.
<= and >= stand for "less or equal than" and "greater or equal than".

As with many enumeration types, the order is a bit arbitrary

    λ> minBound :: Char
    '\NUL'
    λ> maxBound :: Char
    '\1114111'
    λ> ['$'..'Z']
    "$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            -- so * will be < than, say, A
    λ> '*' < 'A'
    True

Does that answer your question?