# thbel's solution

## to Matching Brackets in the OCaml Track

Published at Apr 29 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


## 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)
(* use a stack based approach and implement ListStack from https://www.cs.cornell.edu/courses/cs3110*)

open Base

let push stck c = c::stck

let peek stck = match stck with
| [] -> 'n'
| x::_ -> x

let pop stck =  match stck with
| [] -> failwith "pooop"
| _::xs -> xs

let is_closing c c' =
match c, c' with
| '(', ')' -> true
| '{', '}' -> true
| '[', ']' -> true
| _,_ -> false

let rec balanced stck lst =
match lst, stck with
| [], [] -> true
| [], _ -> false
| x::xs, _ when List.mem ['(';'{';'[';] x ~equal:Char.equal -> balanced (push stck x) xs
| x::xs, _ when List.mem [')';'}';']';] x ~equal:Char.equal -> if (is_closing (peek stck) x) then (balanced (pop stck) xs) else false
| _::xs, _ -> balanced stck xs

let are_balanced s =
s |> String.to_list |> balanced []