Question

I’m having trouble getting this started, as in, I’m not sure what is exactly happening with this function. What it’s supposed to do is take in 2 parameters, a character, and a string, then output a list of strings that are separated by that character.

For example,

break ',' "abc,def,ghi"

should output [“abc”,”def”,”ghi”]

I am given the code, and I’m supposed to fill in the “?”s

break ? [] = ?
break n xs = brk n xs ?
 where
 brk n xs acc
  | xs == [] = ?
  | n == ? xs = ? ++ break n (? xs)
  | ? = brk n (? xs) (acc ++ ?)

I’m not sure how to approach this or how the acc helps with this problem. The only idea I have is that the first line should be

break _ [] = []

If anyone can help me get started with this problem, that would be great! Thanks!

Answer 1

acc is an abbreviation for “accumulator”—you use it to accumulate your results as you recurse. Look at the types of break and brk for some clues:

break :: (Eq a) => a -> [a] -> [[a]]
brk   :: (Eq a) => a -> [a] -> [[a]] -> [[a]]

Or more concretely:

break :: Char -> String -> [String]
brk   :: Char -> String -> [String] -> [String]

Here are some questions to help you figure out how to implement brk:

• What should the initial set of results be?

• What should you get when you split an empty list?

• What should you do when the splitting character appears at the start of the string?

• What should you do otherwise?