 # revazi's solution

## to Bracket Push in the PureScript Track

Published at Oct 10 2018 · 0 comments
Instructions
Test suite
Solution

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

Ginna Baker

## Submitting Incomplete Solutions

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

### Main.purs

module Test.Main where

import Prelude

import Effect (Effect)
import Test.Unit.Assert as Assert
import Test.Unit (TestSuite, suite, test)
import Test.Unit.Main (runTest)
import BracketPush (isPaired)

main :: Effect Unit
main = runTest suites

suites :: TestSuite
suites = do
suite "BracketPush.isPaired" do

test "paired square brackets" $Assert.equal true (isPaired "[]") test "empty string"$
Assert.equal true
(isPaired "")

test "unpaired brackets" $Assert.equal false (isPaired "[[") test "wrong ordered brackets"$
Assert.equal false
(isPaired "}{")

test "paired with whitespace" $Assert.equal true (isPaired "{ }") test "simple nested brackets"$
Assert.equal true
(isPaired "{[]}")

test "several paired brackets" $Assert.equal true (isPaired "{}[]") test "paired and nested brackets"$
Assert.equal true
(isPaired "([{}({}[])])")

test "unopened closing brackets" $Assert.equal false (isPaired "{[)][]}") test "unpaired and nested brackets"$
Assert.equal false
(isPaired "([{])")

test "paired and wrong nested brackets" $Assert.equal false (isPaired "[({]})") test "math expression"$
Assert.equal true
(isPaired "(((185 + 223.85) * 15) - 543)/2")

test "complex latex expression" $Assert.equal true (isPaired "\\left(\\begin{array}{cc} \\frac{1}{3} & x\\\\ \\mathrm{e}^{x} &... x^2 \\end{array}\\right)") module BracketPush ( isPaired ) where import Prelude import Data.List (List(..), fromFoldable) import Data.Maybe (Maybe(..)) import Data.String.CodeUnits (toCharArray) data Bracket = SquareBracket | RoundedBracket | CurlyBracket | AngleBracket derive instance eqBracket :: Eq Bracket openBracket :: Char -> Maybe Bracket openBracket '[' = Just SquareBracket openBracket '(' = Just RoundedBracket openBracket '{' = Just CurlyBracket openBracket '<' = Just AngleBracket openBracket _ = Nothing closeBracket :: Char -> Maybe Bracket closeBracket ']' = Just SquareBracket closeBracket ')' = Just RoundedBracket closeBracket '}' = Just CurlyBracket closeBracket '>' = Just AngleBracket closeBracket _ = Nothing isPaired :: String -> Boolean isPaired a = isPaired' Nil$ fromFoldable (toCharArray a)

isPaired' :: List Bracket -> List Char -> Boolean
isPaired' bs Nil = case bs of
Nil -> true
Cons _ _ -> false
isPaired' bs (Cons c cs) = case openBracket c of
Just b -> isPaired' (Cons b bs) cs
Nothing -> case closeBracket c of
Just b -> case bs of
Cons b' bs' -> if b == b'
then isPaired' bs' cs
else false
Nil -> false
Nothing -> isPaired' bs cs