🎉 Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io 🎉
Avatar of leojpod

leojpod's solution

to Matching Brackets in the Elm Track

Published at Jan 24 2020 · 0 comments
Instructions
Test suite
Solution

Given a string containing brackets [], braces {}, parentheses (), or any combination thereof, verify that any and all pairs are matched and nested correctly.

Elm Installation

Refer to the Installing Elm page for information about installing elm.

Writing the Code

The code you have to write is located inside the src/ directory of the exercise. Elm automatically installs packages dependencies the first time you run the tests so we can start by running the tests from the exercise directory with:

$ elm-test

To automatically run tests again when you save changes:

$ elm-test --watch

As you work your way through the tests suite in the file tests/Tests.elm, be sure to remove the skip <| calls from each test until you get them all passing!

Source

Ginna Baker

Submitting Incomplete Solutions

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

Tests.elm

module Tests exposing (tests)

import Expect
import MatchingBrackets exposing (isPaired)
import String
import Test exposing (..)


tests : Test
tests =
    describe "MatchingBrackets"
        [ test "paired square brackets" <|
            \_ ->
                Expect.equal True (isPaired "[]")
        , skip <|
            test "empty string" <|
                \_ ->
                    Expect.equal True (isPaired "")
        , skip <|
            test "unpaired brackets" <|
                \_ ->
                    Expect.equal False (isPaired "[[")
        , skip <|
            test "wrong ordered brackets" <|
                \_ ->
                    Expect.equal False (isPaired "}{")
        , skip <|
            test "wrong closing bracket" <|
                \_ ->
                    Expect.equal False (isPaired "{]")
        , skip <|
            test "paired with whitespace" <|
                \_ ->
                    Expect.equal True (isPaired "{ }")
        , skip <|
            test "partially paired brackets" <|
                \_ ->
                    Expect.equal False (isPaired "{[])")
        , skip <|
            test "simple nested brackets" <|
                \_ ->
                    Expect.equal True (isPaired "{[]}")
        , skip <|
            test "seceral paired brackets" <|
                \_ ->
                    Expect.equal True (isPaired "{}[]")
        , skip <|
            test "paired and nested brackets" <|
                \_ ->
                    Expect.equal True (isPaired "([{}({}[])])")
        , skip <|
            test "unopened closing brackets" <|
                \_ ->
                    Expect.equal False (isPaired "{[)][]}")
        , skip <|
            test "unpaired and nested brackets" <|
                \_ ->
                    Expect.equal False (isPaired "([{])")
        , skip <|
            test "paired and wrong nested brackets" <|
                \_ ->
                    Expect.equal False (isPaired "[({]})")
        , skip <|
            test "math expression" <|
                \_ ->
                    Expect.equal True (isPaired "(((185 + 223.85) * 15) - 543)/2")
        , skip <|
            test "complex latex expression" <|
                \_ ->
                    Expect.equal True (isPaired "\\left(\\begin{array}{cc} \\frac{1}{3} & x\\\\ \\mathrm{e}^{x} &... x^2 \\end{array}\\right)")
        ]
module MatchingBrackets exposing (isPaired)


type TypeOfBracket
    = Bracket
    | Brace
    | Parenthesis


isPaired : String -> Bool
isPaired =
    String.toList
        >> List.indexedMap Tuple.pair
        >> List.foldl
            (\( position, char ) res ->
                res
                    |> Result.andThen
                        (\list ->
                            case char of
                                '{' ->
                                    Ok <| Brace :: list

                                '}' ->
                                    case list of
                                        Brace :: rest ->
                                            Ok rest

                                        _ ->
                                            Err <| "miss matching '}' at position " ++ String.fromInt position

                                '[' ->
                                    Ok <| Bracket :: list

                                ']' ->
                                    case list of
                                        Bracket :: rest ->
                                            Ok rest

                                        _ ->
                                            Err <| "miss matching '}' at position " ++ String.fromInt position

                                '(' ->
                                    Ok <| Parenthesis :: list

                                ')' ->
                                    case list of
                                        Parenthesis :: rest ->
                                            Ok rest

                                        _ ->
                                            Err <| "miss matching '}' at position " ++ String.fromInt position

                                _ ->
                                    Ok list
                        )
            )
            (Ok [])
        >> Result.map List.isEmpty
        >> Result.withDefault False

Community comments

Find this solution interesting? Ask the author a question to learn more.

leojpod's Reflection

I'd wish to change the return type of this function to return a `Result ParsingError ()` which would be a bit more interesting in terms of type definition and such.