ðŸŽ‰ Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io ðŸŽ‰

Published at Mar 14 2021
·
0 comments

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 where
import Data.Array (foldl, snoc, null, last, tail, singleton, fromFoldable, take, length, init)
import Data.Maybe (Maybe(..), fromJust)
import Data.String.CodeUnits (toCharArray)
import Data.Tuple (Tuple(..))
import Prelude (($), (==), (||), (/), (+), (-))
bracketToInt :: Char -> Maybe Int
bracketToInt '(' = Just 1
bracketToInt '[' = Just 2
bracketToInt '{' = Just 3
bracketToInt ')' = Just 4
bracketToInt ']' = Just 5
bracketToInt '}' = Just 6
bracketToInt _ = Nothing
stackBrackets :: Maybe (Array Int) -> Char -> Maybe (Array Int)
stackBrackets Nothing _ = Nothing
stackBrackets (Just brackets) c
| c == '[' || c == '(' || c == '{' = case (bracketToInt c) of
Just bracketInt -> Just $ snoc brackets bracketInt
Nothing -> Nothing
stackBrackets (Just brackets) c =
case { l: last brackets, bi: (bracketToInt c) } of
{l: _, bi: Nothing} -> Just brackets
{l: Just lastBracket, bi: Just bracketInteger} -> if (lastBracket + 3) == bracketInteger then init brackets else Nothing
_ -> Nothing
isPaired :: String -> Boolean
isPaired pairs = case foldl stackBrackets (Just ([] :: Array Int)) $ toCharArray pairs of
Just brackets -> null brackets
Nothing -> false
```

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?

Level up your programming skills with 3,450 exercises across 52 languages, and insightful discussion with our volunteer team of welcoming mentors.
Exercism is
**100% free forever**.

## Community comments