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# mstream's solution

## to Bracket Push in the PureScript Track

Published at Oct 28 2020 · 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.Foldable
( foldl
)
import Data.List
( List
, (:)
, null
)
import Data.Set
( Set
, fromFoldable
, member
)
import Data.String.CodeUnits
( toCharArray
)

isPaired :: String -> Boolean
isPaired =
null <<<
foldl r mempty <<<
toCharArray
where
parentheses :: Set Char
parentheses = fromFoldable
[ '(', ')', '[', ']', '{', '}' ]
r :: List Char -> Char -> List Char
r ('(' : ps) ')' = ps
r ('[' : ps) ']' = ps
r ('{' : ps) '}' = ps
r ps c
| c member parentheses = c : ps
| otherwise = ps