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

Published at Jul 13 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.

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 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
```

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