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to Word Count in the Elm Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given a phrase, count the occurrences of each word in that phrase.

For example for the input "olly olly in come free"

olly: 2
in: 1
come: 1
free: 1

Elm Installation

Refer to the Exercism help page for Elm installation and learning resources.

Writing the Code

The first time you start an exercise, you'll need to ensure you have the appropriate dependencies installed.

$ elm-package install --yes

Execute the tests with:

$ elm-test

Automatically run tests again when you save changes:

$ elm-test --watch

As you work your way through the test suite, be sure to remove the skip <| calls from each test until you get them all passing!

Source

This is a classic toy problem, but we were reminded of it by seeing it in the Go Tour.

Submitting Incomplete Solutions

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

Tests.elm

module Tests exposing (..)

import Dict exposing (Dict)
import Expect
import Test exposing (..)
import WordCount exposing (wordCount)


tests : Test
tests =
    describe "Word Count"
        [ test "count one word" <|
            \() ->
                Expect.equal [ ( "word", 1 ) ]
                    (wordCount "word" |> Dict.toList)
        , skip <|
            test "count one of each word" <|
                \() ->
                    Expect.equal [ ( "each", 1 ), ( "of", 1 ), ( "one", 1 ) ]
                        (wordCount "one of each" |> Dict.toList)
        , skip <|
            test "multiple occurrences of a word" <|
                \() ->
                    Expect.equal [ ( "blue", 1 ), ( "fish", 4 ), ( "one", 1 ), ( "red", 1 ), ( "two", 1 ) ]
                        (wordCount "one fish two fish red fish blue fish" |> Dict.toList)
        , skip <|
            test "ignore punctuation" <|
                \() ->
                    Expect.equal [ ( "as", 1 ), ( "car", 1 ), ( "carpet", 1 ), ( "java", 1 ), ( "javascript", 1 ) ]
                        (wordCount "car : carpet as java : javascript!!&@$%^&" |> Dict.toList)
        , skip <|
            test "include numbers" <|
                \() ->
                    Expect.equal [ ( "1", 1 ), ( "2", 1 ), ( "testing", 2 ) ]
                        (wordCount "testing, 1, 2 testing" |> Dict.toList)
        , skip <|
            test "normalize case" <|
                \() ->
                    Expect.equal [ ( "go", 3 ), ( "stop", 2 ) ]
                        (wordCount "go Go GO Stop stop" |> Dict.toList)
        ]

elm-package.json

{
    "version": "3.0.0",
    "summary": "Exercism problems in Elm.",
    "repository": "https://github.com/exercism/elm.git",
    "license": "BSD3",
    "source-directories": [
        ".",
        ".."
    ],
    "exposed-modules": [],
    "dependencies": {
        "elm-lang/core": "5.0.0 <= v < 6.0.0",
        "elm-community/elm-test": "4.0.0 <= v < 5.0.0"
    },
    "elm-version": "0.18.0 <= v < 0.19.0"
}
module WordCount exposing (..)
import Dict exposing (Dict)
import Char

wordCount: String -> Dict String Int
wordCount sentence =
    sentence
        |> removePunctuation
        |> String.words
        |> List.foldl populateDict Dict.empty

removePunctuation: String -> String
removePunctuation sentence =
    sentence
        |> String.toLower
        |> String.filter isLetterDigitOrWhitespace

isLetterDigitOrWhitespace: Char -> Bool
isLetterDigitOrWhitespace char =
    Char.isLower char ||
    Char.isDigit char ||
    char == ' '

populateDict: comparable -> Dict comparable Int -> Dict comparable Int
populateDict word dict =
    Dict.update word incrementValue dict

incrementValue : Maybe Int -> Maybe Int
incrementValue maybe =
    (Maybe.withDefault 0 maybe) + 1
        |> Just

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