# goderich's solution

## to Matching Brackets in the OCaml Track

Published at Jul 01 2020 · 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. 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


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## 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

(* I'm using a short-circuiting fold and a list instead
* of a stack, this way I'm working with language
* primitives in a functional way.
*
* I pattern matched against different closing brackets
* separately, because I couldn't see a good way to
* abstract this out, but also because I don't see the
* point. I think what I have now is much more readable
* at the expense of maybe an extra two lines. *)

let are_balanced s =
String.fold_until s ~init:[]
~f:(fun acc c -> match c, acc with
| '(', _ | '[', _ | '{', _ -> Continue (c :: acc)
| ')', ('('::tl)
| ']', ('['::tl)
| '}', ('{'::tl) -> Continue tl
| ')', _ | ']', _ | '}', _ -> Stop false
| _ -> Continue acc)
~finish:List.is_empty