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## to Bracket Push in the PureScript Track

Published at Jul 13 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" $Assert.equal true (isPaired "\\left(\\begin{array}{cc} \\frac{1}{3} & x\\\\ \\mathrm{e}^{x} &... x^2 \\end{array}\\right)") module BracketPush ( isPaired ) where import Data.Array (elem, foldM) import Data.List (List(..), (:)) import Data.Maybe (Maybe(..)) import Data.String (toCharArray) import Data.Tuple (Tuple(..), fst, lookup, snd) import Prelude (flip, map, otherwise, ($), (<$>), (==)) isPaired ∷ String → Boolean isPaired = isPaired' [ (Tuple '(' ')') , (Tuple '[' ']') , (Tuple '{' '}') ] isPaired' :: Array (Tuple Char Char) → String → Boolean isPaired' ps xs = Just Nil == (foldM f Nil$ toCharArray xs)
where
f stack ch
| ch elem map snd ps =
case stack of
(top : stack') -> if ch == top then Just stack' else Nothing
_ -> Nothing
| ch elem map fst ps = (flip (:) stack) <\$> lookup ch ps
| otherwise = Just stack

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