问题
I have a very simple question: Given a function accepting a char and returning a string
test :: Char -> [String]
how can one convert the char into a string? I'm confused over the two types.
回答1:
In Haskell String is an alias for [Char]:
type String = [Char]
If you just want a function that converts a single char to a string you could e.g. do
charToString :: Char -> String
charToString c = [c]
If you prefer pointfree style you could also write
charToString :: Char -> String
charToString = (:[])
回答2:
A String is just a [Char]
But that's just a nice way of saying
'H':'E':'L':'L':'O':[]
So to make it a [String] we could do:
['H':'E':'L':'L':'O':[]]
回答3:
Another way would be using
return . return
Since return for lists is defined as :[]
回答4:
Note that you can convert any type implementing the Show type class to a string using show:
(Show a) => a -> String
Because Char implements this, the function is already written for you!
来源：https://stackoverflow.com/questions/6168739/char-to-string-function