open Str

let main () =
  (* This tests whether a pattern matches a string. *)
  let match_result = string_match (regexp "p[a-z]+ch") "peach" 0 in
  Printf.printf "%b\n" match_result;

  (* We use the Str.regexp function to compile an optimized Str.regexp struct. *)
  let r = regexp "p[a-z]+ch" in

  (* Many functions are available on these structs. Here's a match test like we saw earlier. *)
  Printf.printf "%b\n" (string_match r "peach" 0);

  (* This finds the match for the regexp. *)
  Printf.printf "%s\n" (matched_string (string_match r "peach punch" 0));

  (* This also finds the first match but returns the start and end indexes for the match. *)
  let (start_idx, end_idx) = matched_group 0 (string_match r "peach punch" 0) in
  Printf.printf "idx: [%d %d]\n" start_idx end_idx;

  (* The group variants include information about both the whole-pattern matches and the submatches. *)
  let result = string_match r "peach punch" 0 in
  Printf.printf "[%s %s]\n" (matched_string result) (matched_group 1 result);

  (* To find all matches for a regexp, we can use a recursive function. *)
  let rec find_all_matches str pos =
    try
      let result = search_forward r str pos in
      (matched_string result) :: (find_all_matches str (result + 1))
    with Not_found -> []
  in
  let all_matches = find_all_matches "peach punch pinch" 0 in
  Printf.printf "%s\n" (String.concat " " all_matches);

  (* The Str module can also be used to replace subsets of strings with other values. *)
  Printf.printf "%s\n" (global_replace (regexp "p[a-z]+ch") "<fruit>" "a peach");

  (* We can use a custom function to transform matched text. *)
  let upper_case_match s = String.uppercase_ascii (matched_string s) in
  Printf.printf "%s\n" (global_substitute (regexp "p[a-z]+ch") upper_case_match "a peach")

let _ = main ()