I'm trying to implement a function that returns the next letter in alphabetical order. For example:
> returnNext 'A'
'B'
But also:
> returnNext 'Z'
'A'
The function should thus cycle between char codes in alphabetical order (mod 26).
Two ways come to mind
import Data.Char
returnNext c = chr (((1 + ord c - ord 'A') `mod` 26) + ord 'A')
Which is kind of ugly to say the least.
And:
returnNext 'Z' = 'A'
returnNext c = chr (ord c + 1)
Both behave differently when not given a letter of the alphabet, but since you didn't specify what should happen in this case I'll assume it's OK.
来源：https://stackoverflow.com/questions/20746646/how-to-return-the-next-letter-in-the-alphabet-of-given-letter-wrapped-around-in