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to Gigasecond in the Elm Track

Published at Jul 13 2020 · 0 comments
Test suite

Given a moment, determine the moment that would be after a gigasecond has passed.

A gigasecond is 10^9 (1,000,000,000) seconds.

Elm Installation

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

Writing the Code

The first time you start an exercise, you'll need to ensure you have the appropriate dependencies installed. Thankfully, Elm makes that easy for you and will install dependencies when you try to run tests or build the code.

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!


Chapter 9 in Chris Pine's online Learn to Program tutorial. http://pine.fm/LearnToProgram/?Chapter=09

Submitting Incomplete Solutions

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


module Tests exposing (tests)

import Expect
import Gigasecond exposing (add)
import Iso8601
import Parser
import Test exposing (..)
import Time

tests : Test
tests =
    describe "Gigasecond"
        [ describe "add"
            [ test "2011-04-25" <|
                \() ->
                    Expect.equal "2043-01-01T01:46:40.000Z"
                        (gigasecond "2011-04-25")
            , skip <|
                test "1977-06-13" <|
                    \() ->
                        Expect.equal "2009-02-19T01:46:40.000Z"
                            (gigasecond "1977-06-13")
            , skip <|
                test "1959-07-19" <|
                    \() ->
                        Expect.equal "1991-03-27T01:46:40.000Z"
                            (gigasecond "1959-07-19")
            , skip <|
                test "full time specified" <|
                    \() ->
                        Expect.equal "2046-10-02T23:46:40.000Z"
                            (gigasecond "2015-01-24T22:00:00.000Z")
            , skip <|
                test "full time with day roll-over" <|
                    \() ->
                        Expect.equal "2046-10-03T01:46:39.000Z"
                            (gigasecond "2015-01-24T23:59:59.000Z")

gigasecond : String -> String
gigasecond date =
    case Iso8601.toTime date of
        Ok posix ->
                |> Gigasecond.add
                |> Iso8601.fromTime

        _ ->
module Gigasecond exposing (add)

import Time

add : Time.Posix -> Time.Posix
add timestamp =
        numMillis =
            Time.posixToMillis timestamp

        millisToAdd =
            (10 ^ 9) * 1000

        futureMillis =
            numMillis + millisToAdd
    Time.millisToPosix futureMillis

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