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Published at Aug 02 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.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
```

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?
- Are there new concepts here that you could read more about to improve your understanding?

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