Advanced Exercism • crystal

Split-Second Stopwatch

Challenge Overview

Keep track of time through a digital stopwatch.

Introduction

You’ve always run for the thrill of it — no schedules, no timers, just the sound of your feet on the pavement. But now that you’ve joined a competitive running crew, things are getting serious. Training sessions are timed to the second, and every split second counts. 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.

Instructions

Your task is to build a stopwatch to keep precise track of lap times.

The stopwatch uses four commands (start, stop, lap, and reset) to keep track of:

The current lap’s tracked time
Previously recorded lap times

What commands can be used depends on which state the stopwatch is in:

Ready: initial state
Running: tracking time
Stopped: not tracking time

Command	Begin state	End state	Effect
Start	Ready	Running	Start tracking time
Start	Stopped	Running	Resume tracking time
Stop	Running	Stopped	Stop tracking time
Lap	Running	Running	Add current lap to previous laps, then reset current lap
Reset	Stopped	Ready	Reset current lap and clear previous laps

Source: Exercism crystal/split-second-stopwatch