迭代 OCaml 中的拆分字符串

Question

Let's say I have a string:

"ab bc cdv gf
ed    aqb ahf sd
abcdef

I want to a) Split it by ' ' and/or '\r\n' , '\t' b) Iterate over newly created list of these substrings, split by separators and match each of them to some criteria (for example, only choose words starting with 'a' , aka ["ab", "ahf", "abcdef"]

Note: also we can't use Str or any other additional libraries.

I came up with some sort of this code:

let f g =
  String.split_on_char ' ' g
  |> List.iter (fun x -> x);;

Obviously though, it shows an error. And even if it worked, it wouldn't have split out the '\r\n' . Instead of List.iter I could have used List.map (fun x -> x) , but I will just get the split (by ' ' character only) list of substrings. So now another question: how can I use

"match (something?) with
| ..." 

in this case? I see no way in adding match into the code above. Do we use the reverse |> and List.iter in this case or is there another way I'm not aware of?

Answer 1

Simple approach: let's just keep splitting on whietspace characters we want to split on, use List.concat_map to maintain a "flat" list, and then reject empty lists.

let s = "ab bc cdv gf ed aqb ahf sd abc\r\ndef"

let split = String.split_on_char in
List.(
  split ' ' s 
  |> concat_map (split '\n')
  |> concat_map (split '\r') 
  |> filter ((<>) "")
)

(* Result:
 * ["ab"; "bc"; "cdv"; "gf"; "ed"; "aqb"; "ahf"; "sd"; "abc"; "def"] 
 *)

You might also use your regular expression library of choice and split on \s+ , but apparently that isn't allowed.