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hendrikniemann's solution

to Bracket Push in the PureScript Track

Published at Jul 13 2018 · 0 comments
Test suite

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


Ginna Baker

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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(..), (:))
import Data.Maybe (Maybe(..))
import Data.String (uncons)
import Data.String.Regex (replace)
import Data.String.Regex.Flags (global)
import Data.String.Regex.Unsafe (unsafeRegex)

isOpen :: Char -> Boolean
isOpen c = c == '(' || c == '[' || c == '{'

matches :: Char -> Char -> Boolean
matches '(' ')' = true
matches '[' ']' = true
matches '{' '}' = true
matches _   _   = false

onlyBrackets :: String -> String
onlyBrackets = replace (unsafeRegex "[^()[\\]{}]" global) ""

isPaired :: String -> Boolean
isPaired = onlyBrackets >>> isPaired' Nil
    isPaired' :: List Char -> String -> Boolean
    isPaired' Nil   ""  = true
    isPaired' stack str = case uncons str of
        Nothing -> false
        Just { head, tail } ->
            if isOpen head
            -- open brackets get pushed to stack
            then isPaired' (head:stack) tail
            -- closed brackets need to match the stack head
            else case stack of
                Nil -> false
                Cons x xs -> matches x head && isPaired' xs tail

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