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Published at Jul 13 2018
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Instructions

Test suite

Solution

Given a string containing brackets `[]`

, braces `{}`

and parentheses `()`

,
verify that all the pairs are matched and nested correctly.

Ginna Baker

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
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
where
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
```

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
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