Avatar of MokuHazushi

MokuHazushi's solution

to Matching Brackets in the OCaml Track

Published at Dec 13 2019 · 0 comments
Instructions
Test suite
Solution

Given a string containing brackets [], braces {}, parentheses (), or any combination thereof, verify that any and all pairs are matched and nested correctly.

Getting Started

  1. Install the Exercism CLI.

  2. Install OCaml.

  3. For library documentation, follow Useful OCaml resources.

Running Tests

A Makefile is provided with a default target to compile your solution and run the tests. At the command line, type:

make

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

Feedback, Issues, Pull Requests

The exercism/ocaml repository on GitHub is the home for all of the Ocaml exercises.

If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue or submit a PR. We welcome new contributors!

Source

Ginna Baker

test.ml

open Base
open OUnit2
open Matching_brackets

let ae exp got _test_ctxt =
  assert_equal exp got ~printer:Bool.to_string

let tests = [
  "paired square brackets" >::
  ae true (are_balanced "[]");
  "empty string" >::
  ae true (are_balanced "");
  "unpaired brackets" >::
  ae false (are_balanced "[[");
  "wrong ordered brackets" >::
  ae false (are_balanced "}{");
  "wrong closing bracket" >::
  ae false (are_balanced "{]");
  "paired with whitespace" >::
  ae true (are_balanced "{ }");
  "partially paired brackets" >::
  ae false (are_balanced "{[])");
  "simple nested brackets" >::
  ae true (are_balanced "{[]}");
  "several paired brackets" >::
  ae true (are_balanced "{}[]");
  "paired and nested brackets" >::
  ae true (are_balanced "([{}({}[])])");
  "unopened closing brackets" >::
  ae false (are_balanced "{[)][]}");
  "unpaired and nested brackets" >::
  ae false (are_balanced "([{])");
  "paired and wrong nested brackets" >::
  ae false (are_balanced "[({]})");
  "paired and incomplete brackets" >::
  ae false (are_balanced "{}[");
  "too many closing brackets" >::
  ae false (are_balanced "[]]");
  "math expression" >::
  ae true (are_balanced "(((185 + 223.85) * 15) - 543)/2");
  "complex latex expression" >::
  ae true (are_balanced "\\left(\\begin{array}{cc} \\frac{1}{3} & x\\\\ \\mathrm{e}^{x} &... x^2 \\end{array}\\right)");
]

let () =
  run_test_tt_main ("matching-brackets tests" >::: tests)
open Base
exception Error of string

let are_balanced s =
        let is_open_bracket c = 
                List.exists ['(';'{';'['] ~f:(fun k -> c==k)
        in
        let is_close_bracket c =
                List.exists [')';'}';']'] ~f:(fun k -> c==k)
        in
        let bracket_matches a b =
                List.exists [('(',')');('{','}');('[',']')] ~f:(fun k -> (fst k)==a && (snd k)==b)
        in
        let check_bracket_order openned_bracket_l b =
                if is_open_bracket b then
                        b::openned_bracket_l
                else if is_close_bracket b then
                        match openned_bracket_l with
                        | h::t when (bracket_matches h b) -> t
                        | h::_ when not (bracket_matches h b) -> raise (Error "Bracket order error")
                        | [] -> raise (Error "No openned bracket error")
                else openned_bracket_l
        in
        try
                String.to_list s
                |> List.fold ~init:[] ~f:check_bracket_order
                |> List.is_empty
        with Error _ -> false
;;

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?