试图在haskell中获得2个字符串的首字母

Question

initt [f:_] [l:_] = f ++ " " ++ l

And then i call

initt "First" "Last"

I get an error, saying Couldn't match type 'Char' with '[Char]'

I really don't get it.

Answer 1

I think you want

initt (f:_) (l:_) = [f, ' ', l]

[f:_] is equivalent to [(f:_)] which would match something like ["First"]

Also (++) works on strings, while f & l are supposed to be chars. At best, you could do something like [c] ++ " " ++ [l] but [f, ' ', 'l'] is much better & simpler.

Answer 2

++ is list concatenation. Either pack f and l into lists:

[f] ++ " " ++ [l]

Or create it like Ingo suggested:

[f, ' ', l]

Also, pattern matching on head:tail implies it's a list, so instead of [f:_] , you need simply (f:_) .

Which brings us to the whole solution:

initt (f:_) (l:_) = [f, ' ', l]