Programming a Time Machine

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PROGRAMMING A TIME MACHINE WITH AN EVENT-BASED LANGUAGE THAT USES RISK-BASED TESTING DAVE COPELAND • @davetron5000

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OUR GOALS • Intro to time travel using the Timeline Programming Language • Understand Timeline's design decisions so you can apply them: • To your API or Library Designs • To your own programming languages • To the way you approach developer or user experience

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TIMELINE BASICS • An event-based programming language to program a one-time flight plan for a specific journey • Eschews unit tests for a risk-assessment based on Monte Carlo simulations • An extreme focus on observability - what will the program do? what did the program do?

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HELLO TIMELINE on vortex established [] { send disconnect [] now }

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WHAT PROBLEM DOES TIMELINE SOLVE?

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REMEDIAL TEMPORAL MECHANICS HOW DOES TIME TRAVEL WORK?

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TIME TRAVEL IS SPACE TRAVEL NOW THEN

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DRS NEIL BELL & CHRIS CLARKE • 10 years validating the approach • 5 more to make it practicable • Dr. Bell focused on hardware • Dr. Clarke on firmware & software • Result is the Time Space Manifold (TSM)

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THE PROBLEM

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TRAVEL HAPPENS THROUGH A VORTEX THAT INTERSECTS SPACE

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THE PROBLEM SPACE HAS A LOT OF STUFF IN IT

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AND IT COULD BE IN OUR WAY

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THE PROBLEM AND HITTING IT WOULD BE BAD

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AND…THE TRIP IS JUST MILLI- SECONDS

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DR. CLARKE'S FIRST SOLUTION A GENERAL PURPOSE AUTOMATED PILOT

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ONE PROBLEM THE 2043 BAN ON NEURAL NETWORKS AND MACHINE LEARNING "Flags and ofﬁces" by 4nitsirk is licensed under CC BY-SA 2.0

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BUT REAFFIRMS THE REASON FOR THE BAN THE FIRST WAIVER IS GRANTED • A generalized pilot was created based on vast training data about our universe • First flight was a success, however the second was disasterous • Machine Learning algorithms are inherently incomprehensible and unpredictable • Impossible to explain the behavior observed • And therefore impossible to predict

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FORGET THE GENERAL AND FOCUS ON THE SPECIFIC - SOLVE THE PROBLEM IN FRONT OF US EACH TIME

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CONSEQUENCES • Instead of a general pilot, write a flight plan for each flight • Use a language that makes it obvious how the system will behave when flight happens • Use simulation instead of specification to understand the risks with a given flight plan • Produce comprehensive output about what actually happened.

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— Timeline's Core Value THE MOST IMPORTANT THING ABOUT A PROGRAM IS WHAT IT WILL DO. THE SECOND IS WHAT IT DID. ” “

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SUCCESS! 100 YEAR BOTTLE AGED RUM FIRST FLIGHT WITH A SINGULAR FLIGHT PLAN

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HELLO (AGAIN) TIMELINE on vortex established [] { send disconnect [] now } ALL CODE IS IN RESPONSE TO AN EVENT NO RETURN VALUES OR I/O - YOU CAN ONLY SEND EVENTS

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LET'S TRY IT > timeline plan.timeline Success..............98.00% Failure..............02.00% Hardware failure..........02.00% Failed connection..............01.23% Disconnect failed..............00.77% Seed: 98798798743 98% CHANCE EVERYTHING WORKS AS EXPECTED FUNNY STORY

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TESTING IN PRODUCTION 5 minutes ago disconnect failed office chair

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TO THE MOON AS OF LAST MONTH A REAL TRIP

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CHARTING A COURSE • A destination in space • A length of time to go back • The size and mass of what is traveling

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INTERNATIONAL CELESTIAL REFERENCE FRAME

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INTERGALACTIC CELESTIAL REFERENCE FRAME

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REMEMBER, THERE IS NO I/O—ONLY EVENTS on start [] { send trip details [ destination:[ ascension:60º23'42" declination:75º02'12" distance:384,402km duration:1,296,000s ] traveler:[ weight:90kg dimensions: [ width:1m height:2m depth:0.3m ] ] ] now } ICRF COORDINATE HOW FAR BACK CUBE THAT COMPLETELY ENCLOSES THE TRAVELER STANDARD LIBRARY - TRIGGERS THE VORTEX

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OK, WHAT IS GOING ON? HOW IS THAT A PROGRAM?

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on start [] { } KEYWORD EVENT NAME PARAMS LIST (THIS ONE IS BLANK)

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send trip details [ destination:[ … ] traveler:[ … ] ] now KEYWORD EVENT NAME WHEN TO TRIGGER THE EVENT PARAMS TO THE EVENT - NAMED

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destination:[ ascension:60º23'42" declination:75º02'12" distance:384,402km duration:1,296,000s ] BRACKETS ARE A CONSTRUCTOR THESE ARE TYPED LITERALS type Destination [ ascension:Angle declination:Angle distance:Distance duration:Time ]

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OK, BUT WHY IS IT LIKE THAT?

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LANGUAGE CHOICES send trip details [ destination:[ … ] traveler:[ … ] ] now send disconnect [] now ALWAYS USE BRACKETS - CONSISTENCY ALWAYS USE BRACKETS - CONSISTENCY ALSO, THEY ARE EASIER TO TYPE THAN PARENS NO NEED FOR QUOTES - IT'S OBVIOUS WHAT THE EVENT NAMES ARE

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LANGUAGE CHOICES destination:[ ascension:60º23'42" declination:75º02'12" distance:384,402km duration:1,296,000s ] LITERALS ARE TRUE LITERALS, NOT NUMBERS WE ASCRIBE MEANING TO - NO AMBIGUITY LARGE VALUES ARE EASY TO MISTYPE, SO WE REQUIRE COMMAS - THIS CODE IS FOR HUMANS 60º 23' 42" 1,296,000 S

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NOT "TDD" BUT "RDD" - RISK DRIVEN DEVELOPMENT WORKFLOW 1. Provide plan details 2. Simulate the plan 3. Assess the risk of failure 4. Add code only to reduce risk 5. When risk is acceptable - Go!

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LET'S SIMULATE OUR PLAN > timeline plan.timeline Success..............00.00% Failure.............100.00% Hardware failure..........01.23% Failed connection..............01.23% Large Object Collision....98.77% Known Object Collision..........90.45% unknown Object Collision........08.32%

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WHAT ARE WE COLLIDING WITH? > timeline -seed 98798798743 \ --details="Known Object Collision" \ plan.timeline Success..............00.00% Failure.............100.00% Hardware failure..........01.23% Failed connection..............01.23% Large Object Collision....98.77% Known Object Collision..........90.45% Satellite 4F76......................90.45% collision at 86ms unknown Object Collision........08.32% 86MS INTO OUR JOURNEY, WE HIT A SATELLITE

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CONSULT THE STANDARD LIBRARY // Triggered when traveler enters the // vortex to start the trip on traveler entered [] {} // Trigger a change in the vortex heading send adjust vortex direction [ // angle relative to our // current heading direction:Angle ]

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80MS IN, WE ADJUST TO AVOID THE SATELLITE ALLOW 35MS TO PASS IT, THEN ADJUST BACK

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SOME REAL CODE on traveler entered [] { direction is 45º send adjust vortex direction [ direction:direction ] in 80ms reverse-direction is 360º - direction send adjust vortex direction [ direction:reverse-direction ] in 115ms } "=" IS AMBIGUOUS, SO INSTEAD BE VERY CLEAR SINCE "-" IS DEFINED ON ANGLES, THE RESULT IS AN ANGLE DASHES ARE EASY TO TYPE AND EASY TO READ

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YOU CANNOT INLINE EXPRESSIONS on traveler entered [] { direction is 45º send adjust vortex direction [ direction:direction ] in 80ms send adjust vortex direction [ direction:360º - direction ~~~~~~~~~~~~~~~~ \-- must be literal or variable ] in 115ms INLINING INCREASES DENSITY, WHICH REDUCES COMPREHENSIBILITY THIS ALSO FORCES ALL EXPRESSIONS TO HAVE NAMES

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VARIABLE NAMES MUST BE DEFINED WORDS on traveler entered [] { direction is 45º send adjust vortex direction [ direction:direction ] in 80ms rev-direction is 360º - direction send adjust vortex direction [ direction:rev-direction

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VARIABLE NAMES MUST BE DEFINED WORDS on traveler entered [] { direction is 45º send adjust vortex direction [ direction:direction ] in 80ms rev-direction is 360º - direction ~~~~~~~~~~~~~ \-- “rev” is not a word send adjust vortex direction [ direction:rev-direction ABBREVIATIONS OR NON- WORDS HURT COMPREHENSION. ALL VARIABLES MUST BE COMPRISED OF DEFINED WORDS YOU CAN ADD NEW WORDS TO THE DICTIONARY, BUT MUST DEFINE THEM

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HOW'S OUR PLAN LOOK NOW? > timeline plan.timeline Success..............62.00% Failure..............38.00% Hardware failure..........02.23% Failed connection..............01.23% Failed midstream...............01.00% Small Object Collision....34.70% Large Object Collision....01.07% SPACE IS FILLED WITH LOTS OF STUFF WE DON'T TRACK

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WE DON'T KNOW THE SIZE, SHAPE, OR POSITION OF THIS OBJECT

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WE CAN SEND A "PING" TO SEE WHAT'S AHEAD OF US

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IF SOMETHING'S THERE, WE'LL GET TELEMETRY BACK

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STANDARD LIBRARY AGAIN // ask for telemetry send ping [] // When a ping detects an object ahead on collision imminent [ // How many ms ahead of us? distance:Time // Angle inside vortex position:Angle // cube that encompasses // the object's intersection dimensions:Dimension ]

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SEND A PING ONCE WE ENTER on traveler entered [] { «previous code» send ping [] now }

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RESPOND TO THE IMMINENT COLLISION on collision imminent [ distance: position: dimensions: ] { «???» }

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VIEW STRAIGHT AHEAD INSIDE THE VORTEX OBJECT DETECTED BY PING ANGLE OF WHERE IT INTERSECTS

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WE NEED TO MOVE OPPOSITE OF THE ANGLE OF INTERSECTION

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MOVING BY JUST ENOUGH TO AVOID COLLISION

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IF THE OBJECT IS TOO CLOSE, THERE'S NO TIME TO REACT

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STANDARD LIBRARY YET AGAIN // Adjust our speed through the vortex send adjust vortex speed [ speed: Percent ]

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COMPLEX LOGIC 1. If the object is too close, slow down 2. Avoid the object 3. Correct our course 4. If we had to slow down, speed back up

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SAME ALGORITHM, MORE GENERAL adjustment is distance - 2ms adjustment-back is adjustment + 4ms direction is 180º + position « SLOWDOWN LOGIC TBD » send adjust vortex direction [ direction:direction ] in adjustment send adjust vortex direction [ direction:direction ] in adjustment-back send ping [] in adjustment-back

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SLOWING DOWN too-close? = distance < 10ms if too-close? { speed-adjustment is 90% speed-adjustment-back is 110% object-distance-after-speed-adjustment is speed-adjustment-back x distance adjustment is now 1ms adjustment-back is now object-distance-after-speed-adjustment + 5ms send adjust vortex speed [ speed:speed-adjustment ] now send adjust vortex speed [ speed:speed-adjustment-back ] in adjustment-back } else { do nothing } BOOLEANS ARE SPECIAL, SO THEY MUST END IN A "?" REASSIGNMENT IS ERROR- PRONE, SO MUST BE DONE EXPLICITLY BOTH CASES OF AN IF MUST BE HANDLED EXPLICITLY

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INLINE EXPRESSIONS IN CONTROL STATEMENTS? too-close? = distance < 10ms if distance < 10ms { speed-adjustment is 90% speed-adjustment-back is 110% « etc »

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ALL EXPRESSIONS MUST BE NAMED too-close? = distance < 10ms if distance < 10ms { ~~~~~~~~~~~~~~~ \--- must be literal or variable speed-adjustment is 90% speed-adjustment-back is 110% « etc » ALL EXPRESSIONS MUST BE NAMED, EVEN IN CONTROL STRUCTURES

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COMPOUND EXPRESSIONS object-distance-after-speed-adjustment is speed-adjustment-back x distance adjustment is now 1ms adjustment-back is now 110% x distance + 5ms

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COMPOUND EXPRESSIONS - NOT ALLOWED object-distance-after-speed-adjustment is speed-adjustment-back x distance adjustment is now 1ms adjustment-back is now 110% x distance + 5ms ~~~~~~~~~~~~~~~~~~~ \--- All expressions must be named COMPOUND EXPRESSIONS INCREASE DENSITY

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HOW ABOUT NOW? > timeline plan.timeline Success..............95.00% Failure..............05.00% Hardware failure..........02.23% Failed connection..............01.23% Failed midstream...............01.00% Small Object Collision....01.70% Large Object Collision....01.07% 95% CHANCE SUCCESS + 1.23% CHANCE WE CAN'T CONNECT = 96.23% CHANCE OF NOT DYING 95% CHANCE SUCCESS + 1.23% CHANCE WE CAN'T CONNECT = 96.23% CHANCE OF NOT DYING CAN'T FIX THIS

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THE LAST 2.77% • Handling more edge cases requires a lot of complexity • Unit Tests could let us drive that • Early versions of Timeline supported unit testing… • …but it allowed the creation of complex code whose behavior could not be understood or explained • Instead, we focused on observability

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WHAT HAPPENS IN A FAILURE? > timeline plan.timeline \ --black-box-for="Small Object Collision" Success..............95.00% Failure..............05.00% Hardware failure..........02.23% Failed connection..............01.23% Failed midstream...............01.00% Small Object Collision....01.70% Large Object Collision....01.07% Black Box in: small-object-collision.blackbox

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THE BLACK BOX IS…DETAILED Time Trip Time Type Event Source Params 0 0 Trigger start TSM [] 1 0 Handle start plan.timeline:1 [] 2 0 Trigger trip details plan.timeline:2 [ … ] 3 0 Handle trip details TSM [] 5 0 Trigger vortex established TSM [] 6 0 Handle vortex established plan.timeline:5 [] 10 0 Trigger traveler entered TSM [] 11 0 Handle traveler entered plan.timeline:8 []

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THE BLACK BOX IS…DETAILED Time Trip Time Type Event Source Params 13 2 Schedule adjust vortex direction plan.timeline:10 [ direction: 45º ] 14 2 Schedule adjust vortex direction plan.timeline:14 [ direction: 315º ] … … … … … … 90 80 Trigger adjust vortex direction TSM [ direction: 45º ] 125 115 Trigger adjust vortex direction TSM [ direction: 315º ]

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THE BLACK BOX IS…DETAILED Time Trip Time Type Event Source Params 125 115 Trigger adjust vortex direction TSM [ direction: 315º ] 127 117 Trigger vortex adjusted TSM [] 128 118 Trigger collision TSM [ … ] WE ADJUSTED RIGHT INTO SPACE JUNK :(

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NEXT STEPS • Is this a risk we want to mitigate? ➡ Write code to try to mitigate it • Otherwise, decide if we want to go…or not • While testing gives assurance, risk assessment gives confidence

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— Timeline's Core Value THE MOST IMPORTANT THING ABOUT A PROGRAM IS WHAT IT WILL DO. THE SECOND IS WHAT IT DID. ” “

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TAKE AWAYS • Learn more about time travel and Timeline at timeline-lang.com • When designing APIs or languages, consider both the problem you are solving as well as what you value: • Timeline solves a very specific problem • Timeline values observability and predictability, so: • reduce density • require readability/comprehensibility • testing as simulation instead of verification

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THANKS! •Dave Copeland •@davetron5000 on Twitter •davetron5000.com •timeline-lang.com