Question

I have the following function:

convertToStr :: [Int] -> String
convertToStr [] = []
convertToStr (int:ints)
    | length (int:ints) == 1 = ((show (head (drop 0 (int:ints)))) ++ ", ")
    | length (int:ints) == 2 = ((show (head (drop 0 (int:ints)))) ++ ", ") ++ ((show (head (drop 1 (int:ints)))) ++ ", ")

As can be seen above, I have managed to get the following output from this input:

> convertToStr [3,5]
"3, 5, "

I seem, however to be stuck with regard to being able to write a recursive definition. I’d like to convert a list of any length in [Int] elements to a string with that list and not have it limited as such.

Answer 1

Without explicit recursion you can do it using map and intersperse like this

convertToString :: [Int] -> String
convertToString = concat . (intersperse ", ") . map show

Edit: And with manual recursion it’s like

cts [] = ""
cts (x:xs)
   | null xs = show x 
   | otherwise = show x ++ ", " ++ cts xs