# bgraf's solution

## to Matching Brackets in the OCaml Track

Published at Aug 04 2019 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

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. 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

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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 "[({]})");
"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)

### matching_brackets.ml

let are_balanced expr =
let tos_equals stack item =
match stack with
| h::_ when h = item -> true
| _ -> false
in
(* Custom iteration, as we want to realize early return in case
on an unmatching bracket. *)
let rec scan stack = function
| [] -> begin match stack with [] -> true | _ -> false end
| h::t -> begin
match h with
| '(' | '[' | '{' -> scan (h::stack) t
| ')' when tos_equals stack '(' -> scan (List.tl stack) t
| '}' when tos_equals stack '{' -> scan (List.tl stack) t
| ']' when tos_equals stack '[' -> scan (List.tl stack) t
| ')' | ']' |'}' -> false
| _ -> scan stack t
end
in
expr |> String.to_seq |> List.of_seq |>
scan []

### matching_brackets.mli

val are_balanced : string -> bool