Exercism v3 launches on Sept 1st 2021. Learn more! ๐๐๐

Published at Oct 10 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
( isPaired
) where
import Prelude
import Data.List (List(..), fromFoldable)
import Data.Maybe (Maybe(..))
import Data.String.CodeUnits (toCharArray)
data Bracket
= SquareBracket
| RoundedBracket
| CurlyBracket
| AngleBracket
derive instance eqBracket :: Eq Bracket
openBracket :: Char -> Maybe Bracket
openBracket '[' = Just SquareBracket
openBracket '(' = Just RoundedBracket
openBracket '{' = Just CurlyBracket
openBracket '<' = Just AngleBracket
openBracket _ = Nothing
closeBracket :: Char -> Maybe Bracket
closeBracket ']' = Just SquareBracket
closeBracket ')' = Just RoundedBracket
closeBracket '}' = Just CurlyBracket
closeBracket '>' = Just AngleBracket
closeBracket _ = Nothing
isPaired :: String -> Boolean
isPaired a = isPaired' Nil $ fromFoldable (toCharArray a)
isPaired' :: List Bracket -> List Char -> Boolean
isPaired' bs Nil = case bs of
Nil -> true
Cons _ _ -> false
isPaired' bs (Cons c cs) = case openBracket c of
Just b -> isPaired' (Cons b bs) cs
Nothing -> case closeBracket c of
Just b -> case bs of
Cons b' bs' -> if b == b'
then isPaired' bs' cs
else false
Nil -> false
Nothing -> isPaired' bs cs
```

A huge amount can be learned from reading other peopleโs 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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