Question

I’ve been trying many different ways to do this in Haskell, and I can’t for the life of me figure this out.

I want to get a list of names from the user, and if I know the length of the list (let’s assume that is n), I want to prompt the user n times and ask for the i th item at the i’th time.

So far, I have this:

getinput a b
| a == b = []
| otherwise = input:getinput (a+1) b
where input = do
  a <- getLine
  return a

but I keep getting errors.

Strongly appreciate any help!

Answer 1

Problem with your code

• The return type of input is IO String so you just can not append it to a list.
• Similarly the return type of getinput (a+1) b is IO [String] and not just [String].

Here I have corrected your code

getinput a b | a == b = return []
             | otherwise = do
                    i <- getLine
                    rest <- getinput (a+1) b
                    return (i:rest)

A better and more haskellish way

getinput2 n = sequence $ replicate n getLine