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sporto's solution

to Matching Brackets in the OCaml Track

Published at Mar 26 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.

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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

let equal =
    Char.equal

let is_matching a b =
    if equal a '(' && equal b ')' then
        true
    else if equal a '[' && equal b ']' then
        true
    else if equal a '{' && equal b '}' then
        true
    else
        false

let is_opening c =
    equal c '(' || equal c '[' || equal c '{'

let is_closing c =
    equal c ')' || equal c ']' || equal c '}'

let rec consume (stack: char list) (input: char list) : bool =
    match input with
    | [] ->
        List.is_empty stack

    | input_head :: input_rest ->
        if is_opening input_head then
            consume (input_head :: stack) input_rest

        else if is_closing input_head then
            match stack with
            | [] ->
                false

            | stack_head :: stack_rest ->
                if is_matching stack_head input_head then
                    consume stack_rest input_rest
                else
                    false

        else
            consume stack input_rest

let are_balanced input =
    input
        |> String.to_list
        |> consume []

What can you learn from this solution?

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

  • What compromises have been made?
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