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TatriX'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 where

import Prelude

import Control.Monad.Writer (Writer, runWriter, tell)
import Data.Array (elem)
import Data.List (List(..), fromFoldable, null, (:))
import Data.Maybe (fromJust)
import Data.String (toCharArray)
import Data.Tuple (Tuple(..), fst, lookup, snd)
import Partial.Unsafe (unsafePartial)

type BracketPair = Tuple Char Char
type Brackets = Array BracketPair
brackets :: Brackets
brackets = [ Tuple '{' '}'
           , Tuple '[' ']'
           , Tuple '(' ')'

isPaired :: String -> Boolean
isPaired s = fst $ runWriter $ isPaired' brackets s

isPaired' :: Brackets -> String -> Writer (Array String) Boolean
isPaired' bs s = go Nil $ fromFoldable $ toCharArray s where
  go st Nil = pure $ null st
  go st (x : xs)
    | x `elem` closing = do
      tell ["poping " <> show x]
      case st of
        (top : st') -> if x == top then go st' xs else pure false
        _ -> pure false
    | x `elem` opening = do
      tell ["pushing " <> show x]
      go (pair x : st) xs
    | otherwise = do
      tell ["skipping non-bracket" <> show x]
      go st xs

  opening :: Array Char
  opening = fst <$> bs

  closing :: Array Char
  closing = snd <$> bs

  pair :: Char -> Char
  pair c = unsafePartial $ fromJust $  c `lookup` bs

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