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Add new practice exercise split-second-stopwatch (#749)
* Add new practice exercise `split-second-stopwatch` * use aSTate notation * use strings instead of types in test
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‎config.json‎

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"comparison"
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],
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"difficulty": 7
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},
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{
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"slug": "split-second-stopwatch",
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"name": "Split-Second Stopwatch",
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"uuid": "0945769a-6e67-409d-9f11-102112fb8be9",
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"practices": [
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"opaque-types"
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],
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"prerequisites": [
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"opaque-types",
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"custom-types",
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"pattern-matching",
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"strings",
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"lists",
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"result",
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"records"
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],
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"difficulty": 4
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}
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],
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"foregone": [

‎exercises/practice/split-second-stopwatch/.docs/instructions.md‎

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# Instructions
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Your task is to build a stopwatch to keep precise track of lap times.
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The stopwatch uses four commands (start, stop, lap, and reset) to keep track of:
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1. The current lap's tracked time
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2. Previously recorded lap times
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What commands can be used depends on which state the stopwatch is in:
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1. Ready: initial state
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2. Running: tracking time
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3. Stopped: not tracking time
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| Command | Begin state | End state | Effect |
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| ------- | ----------- | --------- | -------------------------------------------------------- |
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| Start | Ready | Running | Start tracking time |
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| Start | Stopped | Running | Resume tracking time |
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| Stop | Running | Stopped | Stop tracking time |
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| Lap | Running | Running | Add current lap to previous laps, then reset current lap |
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| Reset | Stopped | Ready | Reset current lap and clear previous laps |

‎exercises/practice/split-second-stopwatch/.docs/introduction.md‎

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# Introduction
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You've always run for the thrill of it — no schedules, no timers, just the sound of your feet on the pavement.
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But now that you've joined a competitive running crew, things are getting serious.
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Training sessions are timed to the second, and every split second counts.
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To keep pace, you've picked up the _Split-Second Stopwatch_ — a sleek, high-tech gadget that's about to become your new best friend.

‎exercises/practice/split-second-stopwatch/.meta/config.json‎

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{
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"authors": [
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"jiegillet"
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],
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"files": {
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"solution": [
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"src/SplitSecondStopwatch.elm"
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],
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"test": [
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"tests/Tests.elm"
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],
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"example": [
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".meta/src/SplitSecondStopwatch.example.elm"
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]
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},
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"blurb": "Keep track of time through a digital stopwatch.",
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"source": "Erik Schierboom",
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"source_url": "https://github.com/exercism/problem-specifications/pull/2547"
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}

‎exercises/practice/split-second-stopwatch/.meta/src/SplitSecondStopwatch.example.elm‎

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module SplitSecondStopwatch exposing
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( State(..)
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, Stopwatch
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, advanceTime
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, currentLap
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, lap
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, new
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, previousLaps
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, reset
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, start
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, state
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, stop
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, total
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)
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type State
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= Ready
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| Running
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| Stopped
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type Stopwatch
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= Stopwatch
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{ aState : State
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, aCurrentLap : Int
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, aPreviousLaps : List Int
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}
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new : Stopwatch
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new =
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Stopwatch { aState = Ready, aCurrentLap = 0, aPreviousLaps = [] }
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state : Stopwatch -> State
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state (Stopwatch { aState }) =
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aState
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currentLap : Stopwatch -> String
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currentLap (Stopwatch { aCurrentLap }) =
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formatTime aCurrentLap
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previousLaps : Stopwatch -> List String
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previousLaps (Stopwatch { aPreviousLaps }) =
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aPreviousLaps
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|> List.reverse
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|> List.map formatTime
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advanceTime : String -> Stopwatch -> Stopwatch
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advanceTime time (Stopwatch ({ aState, aCurrentLap } as stopwatch)) =
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case aState of
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Running ->
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Stopwatch { stopwatch | aCurrentLap = aCurrentLap + parseTime time }
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_ ->
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Stopwatch stopwatch
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total : Stopwatch -> String
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total (Stopwatch { aCurrentLap, aPreviousLaps }) =
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(aCurrentLap :: aPreviousLaps)
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|> List.sum
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|> formatTime
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start : Stopwatch -> Result String Stopwatch
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start (Stopwatch ({ aState } as stopwatch)) =
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case aState of
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Running ->
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Err "cannot start an already running stopwatch"
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_ ->
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Ok (Stopwatch { stopwatch | aState = Running })
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stop : Stopwatch -> Result String Stopwatch
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stop (Stopwatch ({ aState } as stopwatch)) =
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case aState of
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Running ->
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Ok (Stopwatch { stopwatch | aState = Stopped })
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_ ->
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Err "cannot stop a stopwatch that is not running"
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lap : Stopwatch -> Result String Stopwatch
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lap (Stopwatch ({ aState, aCurrentLap, aPreviousLaps } as stopwatch)) =
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case aState of
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Running ->
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Ok (Stopwatch { stopwatch | aCurrentLap = 0, aPreviousLaps = aCurrentLap :: aPreviousLaps })
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_ ->
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Err "cannot lap a stopwatch that is not running"
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reset : Stopwatch -> Result String Stopwatch
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reset (Stopwatch { aState }) =
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case aState of
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Stopped ->
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Ok new
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_ ->
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Err "cannot reset a stopwatch that is not stopped"
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parseTime : String -> Int
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parseTime time =
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let
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timeValues =
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time
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|> String.split ":"
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|> List.filterMap String.toInt
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in
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case timeValues of
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[ hours, minutes, seconds ] ->
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hours * 3600 + minutes * 60 + seconds
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_ ->
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0
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formatTime : Int -> String
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formatTime time =
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let
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hours =
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time // 3600
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minutes =
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modBy 3600 time // 60
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seconds =
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modBy 60 time
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in
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[ hours, minutes, seconds ]
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|> List.map String.fromInt
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|> List.map (String.padLeft 2 '0')
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|> String.join ":"

‎exercises/practice/split-second-stopwatch/.meta/tests.toml‎

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[ddb238ea-99d4-4eaa-a81d-3c917a525a23]
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description = "new stopwatch starts in ready state"
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[b19635d4-08ad-4ac3-b87f-aca10e844071]
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description = "new stopwatch's current lap has no elapsed time"
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[492eb532-268d-43ea-8a19-2a032067d335]
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description = "new stopwatch's total has no elapsed time"
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[8a892c1e-9ef7-4690-894e-e155a1fe4484]
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description = "new stopwatch does not have previous laps"
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[5b2705b6-a584-4042-ba3a-4ab8d0ab0281]
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description = "start from ready state changes state to running"
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[748235ce-1109-440b-9898-0a431ea179b6]
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description = "start does not change previous laps"
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[491487b1-593d-423e-a075-aa78d449ff1f]
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description = "start initiates time tracking for current lap"
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[a0a7ba2c-8db6-412c-b1b6-cb890e9b72ed]
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description = "start initiates time tracking for total"
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[7f558a17-ef6d-4a5b-803a-f313af7c41d3]
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description = "start cannot be called from running state"
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[32466eef-b2be-4d60-a927-e24fce52dab9]
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description = "stop from running state changes state to stopped"
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[621eac4c-8f43-4d99-919c-4cad776d93df]
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description = "stop pauses time tracking for current lap"
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[465bcc82-7643-41f2-97ff-5e817cef8db4]
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description = "stop pauses time tracking for total"
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[b1ba7454-d627-41ee-a078-891b2ed266fc]
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description = "stop cannot be called from ready state"
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[5c041078-0898-44dc-9d5b-8ebb5352626c]
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description = "stop cannot be called from stopped state"
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[3f32171d-8fbf-46b6-bc2b-0810e1ec53b7]
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description = "start from stopped state changes state to running"
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[626997cb-78d5-4fe8-b501-29fdef804799]
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description = "start from stopped state resumes time tracking for current lap"
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[58487c53-ab26-471c-a171-807ef6363319]
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description = "start from stopped state resumes time tracking for total"
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[091966e3-ed25-4397-908b-8bb0330118f8]
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description = "lap adds current lap to previous laps"
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[1aa4c5ee-a7d5-4d59-9679-419deef3c88f]
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description = "lap resets current lap and resumes time tracking"
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[4b46b92e-1b3f-46f6-97d2-0082caf56e80]
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description = "lap continues time tracking for total"
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[ea75d36e-63eb-4f34-97ce-8c70e620bdba]
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description = "lap cannot be called from ready state"
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[63731154-a23a-412d-a13f-c562f208eb1e]
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description = "lap cannot be called from stopped state"
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[e585ee15-3b3f-4785-976b-dd96e7cc978b]
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description = "stop does not change previous laps"
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[fc3645e2-86cf-4d11-97c6-489f031103f6]
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description = "reset from stopped state changes state to ready"
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[20fbfbf7-68ad-4310-975a-f5f132886c4e]
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description = "reset resets current lap"
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[00a8f7bb-dd5c-43e5-8705-3ef124007662]
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description = "reset clears previous laps"
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[76cea936-6214-4e95-b6d1-4d4edcf90499]
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description = "reset cannot be called from ready state"
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[ba4d8e69-f200-4721-b59e-90d8cf615153]
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description = "reset cannot be called from running state"
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[0b01751a-cb57-493f-bb86-409de6e84306]
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description = "supports very long laps"

‎exercises/practice/split-second-stopwatch/elm.json‎

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{
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"type": "application",
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"source-directories": [
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"src"
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],
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"elm-version": "0.19.1",
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"dependencies": {
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"direct": {
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"elm/core": "1.0.5",
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"elm/json": "1.1.3",
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"elm/parser": "1.1.0",
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"elm/random": "1.0.0",
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"elm/regex": "1.0.0",
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"elm/time": "1.0.0",
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"elm/html": "1.0.0"
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},
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"indirect": {}
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},
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"test-dependencies": {
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"direct": {
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"elm-explorations/test": "2.1.0",
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"rtfeldman/elm-iso8601-date-strings": "1.1.4"
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},
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"indirect": {
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"elm/bytes": "1.0.8",
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"elm/virtual-dom": "1.0.3"
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}
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}
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}

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