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LiamGoodacre's solution

to Bracket Push in the PureScript Track

Published at Aug 02 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.

Source

Ginna Baker

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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.Array as Array
import Data.List (List(..), uncons)
import Data.Maybe (Maybe(..))
import Data.String as String
import Control.Alt ((<|>))
import Control.MonadZero (guard)

data Bracket
  = Paren
  | Curley
  | Square

derive instance eqBracket :: Eq Bracket

parseAtom :: forall r . r -> Char -> String.CodePoint -> Maybe r
parseAtom r c cp =
  if String.codePointFromChar c == cp
    then Just r
    else Nothing

parseOpenBracket :: String.CodePoint -> Maybe Bracket
parseOpenBracket cp =
  parseAtom Paren '(' cp <|>
  parseAtom Curley '{' cp <|>
  parseAtom Square '[' cp

parseCloseBracket :: String.CodePoint -> Maybe Bracket
parseCloseBracket cp =
  parseAtom Paren ')' cp <|>
  parseAtom Curley '}' cp <|>
  parseAtom Square ']' cp

stepParser ::
  List Bracket ->
  String.CodePoint ->
  Maybe (List Bracket)
stepParser stack cp | Just bracket <- parseOpenBracket cp =
  Just (Cons bracket stack)
stepParser stack cp | Just bracket <- parseCloseBracket cp = do
  {head, tail} <- uncons stack
  guard (head == bracket) $> tail
stepParser stack _ =
  Just stack

isPaired :: String -> Boolean
isPaired =
  (Just Nil == _) <<<
  Array.foldRecM stepParser Nil <<<
  String.toCodePointArray

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