Every example world in examples/, as a route: what each one teaches, what it needs first, how to run it and what you should see, and one thing to change and predict before you run it again. Each opens in one workshop tab, where the button Start this world over on the title card puts it back as it began; the manual explains the parts.
Each card says what you do — try it run it and predict, change it change one thing and predict, read it read the robots to predict, build it train a robot of your own — and, apart from that, how much is inside. Tick tried on a card and this browser remembers it.
One visible change, a small robot, a predictable result.
A robot does one thing to what it is given, and stops when its thought no longer fits.
Run: Give the leaning scale to the Swap robot: it swaps the two pans, the scale tips the other way, and the robot stops after one round.
Change and predict: Give it the OTHER scale, the one already the right way round. Predict: does it run, and why not?
A behaviour is a letter to a bird: [move | across | 1/60] every round, and the star slides.
Needs Swap
Run: Press SPACE on the star: it slides right and stops at the table’s edge; "." stops it early. The Mover is on its back: hold the star and press Ctrl+P to go through its door and watch.
Change and predict: In there, pick up the step and type a minus. Predict which way the star goes — then make the number bigger.
Repeated motion: walk a little, turn a little, thirty-six times, and a ring appears. Two robots share the work box.
Needs Moving
Run: Press Start the robot: the planet walks and turns thirty-six times and a ring of dots appears round the sun. Instant shows the ring at once.
Change and predict: Change steps left to 9 before you start. How much of the ring will be drawn? Then try 18.
A repeat inside a repeat: four sides make a square petal, six petals on spokes make a flower — each its own colour from a queue on a nest, and invisible ink keeps it one drawing.
Needs A step-and-turn planet
Run: Press Start the robot: six square petals appear round a centre, each a different colour. The next member button above Trained actions shows each robot.
Change and predict: Set petals left to 3 and next spoke from 240° to 300°. Predict the flower; then sweep it up with Dusty — one thing.
A repeat inside a repeat inside a repeat: twenty segments make a curved petal, petals make a flower, three flowers make a garden — each flower one trail, the pen invisible between stem, leaves and petals.
Needs An easy flower
Run: Press Start the robot: three pens rise from their pots, grow a stem and two leaves, and draw 8, 10 and 12 tilted petals with a golden centre. Instant shows it at once; the team puts its box away when the garden is done.
Change and predict: Set flowers left to 1 and watch one flower. Then in the letters box change “move yaw” from 18 to 20. Predict the petal.
A movement amount that changes over time: gravity shrinks the upward step inside the letter each jump, and the dots draw an arch.
Needs A step-and-turn planet
Run: Press Start the robot: the spark rises and falls in twenty steps and leaves an arch of dots behind. The world opens from the side, where the arch reads.
Change and predict: Set gravity to 0. Predict the shape before running; then try −1/200.
Angles into positions: every tick each angle grows by its own step, modulo 360, and sin and cos badges turn it into a place on a tilted track — three planets and a moon that adds the blue planet’s position to its own.
Needs A jumping sparkAn ellipse
Run: Press Start the robot: the planets go round the sun on their tracks and the moon round the blue planet, for 120 ticks; the periods are 30, 60, 120 and 15 ticks, so everybody comes home together.
Change and predict: Set ticks left to 30. Predict which planet gets all the way round. Then change the blue planet’s degrees per tick to 12 and predict the moon.
Velocity and gravity: each spark keeps three velocities in its record, moves by them every tick and stamps a dot, and gravity comes off the upward one — so it slows, turns and falls. Eight sparks reused for three bursts.
Needs A jumping spark
Run: Press Start the robot: eight coloured sparks rise from the nozzle in arches of dots, hide after thirty ticks, and burst again turned 15 degrees, three times; the last burst’s dots remain.
Change and predict: Set gravity per tick to −1/250. Predict the height of the arches. Then set sideways speed to 0 and predict the shape of a burst.
Optional challenge — a bigger jump than the cards round it: a list split at a number to pick the Nth thing, and three letters to one pad. Skip it for now and come back after Things that talk.
A pad with a robot on its back: a die picks the Nth colour from a list by splitting the list there, and three letters paint the pad.
Needs Moving
Run: Press SPACE on the pad: its colour changes again and again, one of the seven; "." stops it. Ctrl+P on it shows the robot at work.
Change and predict: Open the panel and join another [name | ink] pair on the list, then give the die a face. Predict how often the new colour comes up.
Nests that receive the world, and letters to birds that change it.
The keyboard is a nest: every key lands on it, and a robot dozing on the nest wakes per key.
Needs Moving
Run: Give the work box to the Scribe, then type: each key you press appears on the pad.
Change and predict: Type a space, then Backspace. Predict what the pad says — the Scribe joins whatever arrives.
The pointer is a nest too: a reading of [across | away] each move, and three steps keep a box up to date.
Needs The keyboard
Run: Give the work box to the Watcher and move the pointer over the table: the two numbers in its box follow the pointer.
Change and predict: Stop moving. Predict whether the robot keeps running — an empty nest is a robot asleep.
The pointer reading put inside a [set | position | …] letter: the star follows your hand.
Needs The pointerMoving
Run: Press SPACE on the star and move the pointer over the table: the star comes to your hand and stays with it. The Follower is on the star’s back: Ctrl+P to watch it.
Change and predict: Change the letter to [move | position | …] instead of set. Predict: does the star follow, or run away?
The edge is a reading; a team of robots differ only in the word they expect, and flipping a step is a ×−1 dropped on a number.
Needs Moving
Run: Press SPACE on the star: it runs to the right edge, turns round, runs back, and keeps going. The team is on its back: Ctrl+P to go through its door and watch them take turns.
Change and predict: Take the “at the right” robot out of the team. Predict what happens at the right edge.
Randomness is a die: a die of 3, a −2 and a ×30 land on the turn in turn, then a yaw and a step go to the bird.
Needs Bouncing
Run: Press SPACE on the star: it drifts about the table, turning at random. The Wanderer is on its back: Ctrl+P to watch the die land.
Change and predict: In there, hold the die and type 5. Predict: which way does the star circle, and why?
A stopwatch that is not built in: robots on the number’s own panel ask the computer the time and tell the number.
Needs The pointer
Run: Press SPACE on the number: it counts up the milliseconds; "." rests it, and SPACE goes on from there.
Change and predict: Drop a 0 with a set badge on it and start it again. Predict what it counts from.
The workshop’s own machine answers letters: [query | time | bird], [query | date | bird], [query | clock | bird].
Needs A stopwatch
Run: Take a letter off a notebook page, put a bird of your own in its last hole, and give it to the bird to the computer: the answer — the time, the date or the clock — lands on your bird’s nest.
Change and predict: Ask for the time twice a minute apart. Predict which holes change — and why the date would not.
A Logo turtle that is not built in: a nest for orders, two robots, and a pen — forward and right are messages the turtle already answered.
Needs Bouncing
Run: Drop the turtle pad on the shell’s EDGE — the middle makes it ride on the shell instead of steering it — and press SPACE; give the bird “pendown”, then [forward] and [right 90] four times: a square is drawn on the table.
Change and predict: Give it [right | 120] instead of 90, three times. Predict the shape.
The same turtle in its own frame: yaw, pitch and roll, so it can climb and draw in the air.
Needs A turtle
Run: As the turtle, with pitch and roll orders on the table: give it a pitch and a forward and the line leaves the table and climbs.
Change and predict: Pitch up 45, forward, pitch down 45, forward. Predict where the line ends up.
An orbit from two numbers: a position set each round from a growing angle, sine and cosine as letters.
Needs Wandering
Run: Drop the ellipse pad on the star’s EDGE (the middle would only make it ride on the star) and press SPACE on the star: it goes round and round an ellipse; "." stops it, Ruby lets go.
Change and predict: Change one of the two radii. Predict the shape before you look.
Loops, recursion, lists and a grammar — data a robot reads rather than rules it was taught.
A loop with a scale for its test: the count climbs to N, the beam comes level, and the product goes to a bird.
Needs Swap
Run: Give the two-hole box to the Factorial robot: the count climbs to 5, the scale comes level, and the product, 120, flies off with the bird.
Change and predict: Change 5 to 8 before you start. Predict the answer, and how many rounds it takes.
Recursion by houses: each call sends a copy of itself into two houses and the ones pile up on a nest to be summed.
Needs Factorial
Run: Give the five-hole box to the Fib robot; when the smoke stops, give the [0, nest] box to the Sum robot: it adds the ones up and stops at 21.
Change and predict: Ask for fib(5) instead of fib(8). Predict how many ones arrive.
The same recursion with promises: each call makes two nests and dozes until both answer.
Needs Fibonacci by houses
Run: Give the seven-hole box to the fib robot: houses appear and answer one another, and fib(6) arrives on the nest marked “the answer”.
Change and predict: Watch which house answers first. Predict whether the order matters to the answer.
Live numbers: two numbers that listen to each other, each change landing on an event nest, newest underneath.
Needs The computer
Run: Pull both levers up; drop a +3 on A and a ×2 on B: each change lands on the event nest, the newest underneath, and the other number answers.
Change and predict: Drop a +0 on A. Predict whether B moves — an update that changes nothing is swallowed.
A lazy list, a link at a time: each round one link lands on a nest, and a box with no holes means the end.
Needs Factorial
Run: Give the two-hole box to the FinishList robot: 5, 4, 3, 2, 1 land on the nest one a round, then a box with no holes.
Change and predict: Start from 3 instead of 5. Predict the pile on the nest, top to bottom.
Two lazy lists joined: each link lands inside the promise the last one carried, so the answer grows from the outside in.
Needs A list from n to 1
Run: Give the three-hole box to the FinishAppend robot: the joined list grows on “both lists”, a link a round.
Change and predict: Give it two empty lists. Predict what arrives on “both lists”.
Reversal by houses that wait on one another: the last link settles first.
Needs Appending two lists
Run: Give the four-hole box to the Reverse robot: a house appears for each link, and the list comes back the other way round.
Change and predict: Reverse a one-link list. Predict how many houses appear.
A grammar read as data: a rule is a number, the robot splits a copy of the dictionary there and throws its die to choose.
Needs Reversing a listWandering
Run: Pull the lever: sentences pile up on the nest, a new one each round; pull it again when you have enough.
Change and predict: Add a word to one alternative in the dictionary and pull the lever. Predict which sentences change — the robot is untouched.
A sentence factory in a glass room: the same idea with the rules fixed in the robots.
Needs A grammar as data
Run: Pull the lever on the right wall: sentences come out of the room; click the door to step inside and watch the team make them.
Change and predict: Step inside and read the team. Predict which robot would have to change to add an adjective.
What a house keeps to itself, what a live number tells, and things that are not numbers.
A box with a nest for requests: the robot whose thought carries the word wakes, serves it, and dozes again.
Needs The keyboard
Run: Give the account box to the Teller, then drop a message on the “requests” bird: the balance changes and a slip comes back.
Change and predict: Send [withdraw | 500]. Predict what the balance does, and what comes back.
State sealed in a house: nothing outside can reach the balance; the only way in is a request by bird.
Needs Sally’s account
Run: The house is switched on already. Drop a request on the bird marked “requests”: she flies it in, the Teller answers with a slip, and the balance stays out of reach.
Change and predict: Try the −500 request. Predict which slip the Teller sends, and why the scale decides.
A live number as the balance: two rooms deposit at once and every badge is applied whole, so the total is right however the rounds land.
Needs A bank account in a houseA gauge of live numbers
Run: Pull both levers: the two rooms deposit at once and the balance settles on the same total however the rounds fall.
Change and predict: Predict the final balance before you pull; then predict whether pulling one lever first changes it.
Two houses and a bird between them: a halver and a totaller, the totaller asleep until the post comes.
Needs A bank account in a house
Run: Pull the lever on each house: the bird carries halves from the halver to the totaller, and the total climbs toward 1 without reaching it.
Change and predict: Pull only the totaller’s lever. Predict what it does with no post.
A shelf of behaviours to drop on your own things: sixteen gadgets and a star to try them on.
Needs Bouncing
Run: Drop a gadget on the star and press SPACE on it: the star does what the gadget says; "." stops it; Ruby lets go.
Change and predict: Drop bouncing AND wandering on the star. Predict what happens when it reaches the right wall.
The yard: seven animals on the grass behind the workshop, each a thing with a name.
Needs The shelf of behaviours
Run: Go out through the green back door: seven animals stand on the grass, each with its name.
Change and predict: Drop the wandering gadget on the lion and press SPACE. Predict where it goes.
A button that asks the yard who is there — [query | things | bird] — and gives every animal a wiggle.
Needs The zoo
Run: Go outside and press SPACE on the keeper: every animal in the yard wiggles.
Change and predict: Carry one animal indoors first. Predict how many wiggle.
A toy airplane that takes off, flies a loop and lands: position, up and facing as letters over time.
Needs A turtle in the air
Run: Press SPACE on the airplane: it takes off, flies a loop, and lands.
Change and predict: Change the climb letter’s number. Predict how high the loop goes.
The same flight with a pilot aboard: a thing riding a thing, carried wherever it goes.
Needs An airplane’s flight
Run: Press SPACE on the airplane: it flies its loop with the pilot aboard all the way.
Change and predict: Take the pilot off before take-off. Predict whether the flight changes.
What a sound is: a frequency, seconds and a shape, made by a box dropped on a silent sound.
Needs Swap
Run: Press SPACE on a sound to hear it; drop the box on the silent one and it sings too, the waveform on its screen.
Change and predict: Change 440 to 880. Predict what you hear.
A number dropped on a sound remakes it: ×2 is faster and an octave up, ×−1 plays it backwards.
Needs Tones
Run: Drop the ×2 and the ×−1 on a sound, then SPACE to hear it: faster and an octave up, then backwards.
Change and predict: Drop ×1/2 twice. Predict the pitch.
A tune built the way a sentence is: a note longer each round, joined on the right edge.
Needs Remaking a soundThe keyboard
Run: Give the work box to the Singer: the tune plays, a note longer each round.
Change and predict: Put the pitches on the nest in another order. Predict the tune.
A picture is a pad: it takes the same letters, and rides on a pad like anything else.
Needs Moving
Run: Pick a picture up: the card reads it as a picture. Hold one and press Ctrl with the up arrow: it grows, keeping its own proportions. Drop one in the empty box: it goes in like anything else.
Change and predict: Take a letter such as [set | width | 2] off a notebook page, put a picture’s bird in its last hole, and send it. Predict what happens to the picture.
A notebook files things and a picture is a thing, so a notebook of pictures is an album — and no album was ever written.
Needs Pictures
Run: Point at the album and press the left and right arrow keys, or click its gold corner tabs: six pages, a picture on each. Click a picture to lift it off its page as an ordinary pad; drop it back to file it.
Change and predict: Drop the spare star picture on a blank page. Predict whether the arrow keys reach it — then click the spine and pick up the whole album at once.
A team that names what it sees: seven pictures come off the nest and seven names pile up.
Run: Give the work box to the team leader: seven pictures come off the nest and seven names pile up.
Change and predict: Put the star on the nest twice. Predict how many names arrive.
The full games are the destination; open one behaviour at a time.
Pong from the ordinary parts: a ball, a bat that follows the pointer, a counter, a pitch.
Needs BouncingFollowing the pointer
Run: Set Speed to Instant, point at the pitch and press ENTER, then SPACE: the ball is in play and the bat follows your pointer up and down.
Change and predict: Make the ball’s step bigger. Predict whether the bat can keep up.
The same game built by dropping behaviours from the shelf on the ball and the bat.
Needs Pong, from the partsThe shelf of behaviours
Run: Press SPACE on the ball, then on the bat: the ball bounces about the pitch and the bat follows the pointer.
Change and predict: Take the bouncing gadget off the ball. Predict what the ball does at the wall.
Pong with collisions: the ball bounces off anything on the table, so first clear the court.
Needs Pong, from the shelf
Run: Vacuum the pads away, set Speed to Instant, and press SPACE on the ball: it bounces off the walls and off the bat.
Change and predict: Leave one pad on the court. Predict the rally.
A whole game to be read: a field, a ship on the arrow keys, bullets that vanish, invaders that are hit, a score.
Needs Pong, with collisionsThe keyboard
Run: Point at the dark field and press SPACE; arrows move, up fires: the invaders march, hits take them out, and the score climbs.
Change and predict: Open one invader’s panel. Predict which robot makes it drop down a row.
Each activity has a finite trace to inspect before the argument about its continuation.
Exploring Infinity 1: three rooms in a pipeline, each waking as the first number reaches it, and the evens keep pace with the whole numbers.
Needs Zeno’s postman
Run: Pull the lever on the Add 1 room: the numbers pass down the pipeline and the nests fill, doubles keeping pace with the whole numbers.
Change and predict: Is there an even number on B that is not on doubled? Predict, then watch the two nests fill.
Exploring Infinity 2: the negatives merged in, fairly — Merge waits for the matching negative.
Needs Even numbers
Run: Pull the lever on the Add 1 room: positives and negatives arrive on the merged nest in turn; pull it again when you have seen enough.
Change and predict: Predict the order on the merged nest before it fills.
Exploring Infinity 3: squares, and pairs [n, n²] — a sequence of boxes.
Needs All the integers
Run: Pull the lever on the Add 1 room: squares and [n, n²] pairs land on their nests.
Change and predict: Train a robot of your own for cubes and put it in the squarer’s place. Predict the pairs.
Exploring Infinity 4: every fraction between 0 and 1, the scale pans as holes.
Needs Sequences and pairs
Run: Pull the lever on the All Fractions room: fractions between 0 and 1 arrive on the nest, none missed.
Change and predict: Does 2/4 appear, and 1/2 as well? Predict, then look.
Exploring Infinity 5: the fractions above one are the reciprocals of those below.
Needs All the fractions between 0 and 1
Run: Pull the lever on the All Fractions room: each fraction below one lands with its reciprocal on the other nest.
Change and predict: Predict the first five on the reciprocals nest.
Exploring Infinity 6: every positive rational, five rooms waking in turn, Merge keeping it fair.
Needs The fractions above one
Run: Pull the lever on the All Fractions room: the five rooms wake in turn and the merged nest fills with the positive rationals, none missed.
Change and predict: Predict where 3/2 comes in the merged order relative to 2/3.
Exploring Infinity 7: three nests filling term by term, one for one — the pairing made visible (the post takes a moment, so the counts can differ briefly).
Needs All the positive rationals
Run: Pull the lever on the All Fractions room: the three nests fill together, term for term.
Change and predict: The argument is that ×2 can be undone. Predict what the halving room sends for 3/8.
Exploring Infinity 8: the team takes the first term of the first sequence, the second of the second… a diagonal.
Needs Any interval
Run: Give the three Sequence boxes to the All Sequences bird and pull the three levers: the team takes a term from each in turn and the diagonal piles up.
Change and predict: Predict the first six terms the team takes, in order.
Resort Infinity: cottages without end, guests to house and to move up five — the robots are yours to train.
Needs Counting the sequences
Run: Go outside. Train a robot on the practice letter and give it to the front desk’s bird: each guest is answered and walks to its cottage.
Change and predict: Before you train: predict what the guest at cottage 1 must be told when five more arrive.
Resort Infinity 3: a whole infinite group arrives at a full resort. Adding five will not do — everybody moves from i to 2i, and the newcomers take the odd cottages, 2i − 1.
Needs Resort Infinity
Run: Go outside. Train a mover for the moving office (given [where I live | bird]) and a clerk for the front desk (given [number | group | bird]), give each to its bird, then SPACE on the gold group: everybody moves to the even cottages and the gold guests take the odd ones.
Change and predict: Before you train: which cottages come free when everybody doubles their address? How many is that?
Resort Infinity 4: three infinite groups at once. Everybody moves from i to 4i; guest i of group j takes 4i − j — the group number is in the letter now.
Needs Resort Infinity 3: a new infinite group
Run: Go outside. A mover that multiplies by four, a clerk that computes 4i − j from the number and the group in the letter, and SPACE on three groups: green, plum and teal fill three cottages in every four.
Change and predict: Or solve it as problem 3 three times over. Predict where green guest 2 ends up either way.
Resort Infinity 5: infinitely many infinite groups. Everybody doubles; a newcomer (i, j) gets one whole number n by counting the grid in growing squares — a scale weighs i against j to pick the sum — and takes cottage 2n − 1.
Needs Resort Infinity 4: three infinite groups
Run: Go outside. Give Double to the moving office and Weigh — a team of four: weigh, then one of two sums — to the front desk, then SPACE on the groups: rose, lime and brown take 1, 3, 5, 7, 9, 11 and on into the mist.
Change and predict: Read the pad “Why growing squares”. Predict n for (3, 2) and for (2, 3) before you look at the cottages.
Robots that train robots. Read the pupil’s desired program first, then watch the teacher make it.
A robot that trains a robot: the pupil takes a desk, is shown its step, and has its thought loosened by Ruby.
Needs Factorial
Run: Give the four-hole box to the teacher and press Start: the pupil takes a desk and is taught; then click the pupil and press Start to see it do what it learned.
Change and predict: Predict what the pupil’s thought says after the lesson, before you look.
A teacher whose pupil learns to write to the perch: [set | value | 5] lands on “what it told”.
Needs The teacherMoving
Run: Give the four-hole box to the teacher and press Start: the pupil is taught, and [set | value | 5] lands on “what it told”.
Change and predict: Change the reading before the lesson. Predict the letter that lands.
A teacher that builds the stopwatch: robots that really ask the computer and really tell the number.
Needs TellingA stopwatch
Run: Give the eleven-hole box to the teacher and press Start: four pupils are trained in turn and go on to a number’s panel; take the number out and SPACE on it, and it counts.
Change and predict: Predict which pupil asks and which tells, from their thoughts alone.
A robot solves Resort Infinity in front of you: it trains the two robots and gives them to the birds.
Needs The stopwatch teacherResort Infinity
Run: Go outside and give the teacher its box: it trains the two robots, gives them to the birds, and the guests are housed.
Change and predict: Predict which of the two lessons it gives first, and why the order matters.
A robot solves Resort Infinity 3: teaches the mover (×2), waits for the bell on a nest of its own, teaches the clerk (×2, then −1) on a three-hole letter, and lets the gold group in.
Needs The resort teacherResort Infinity 3: a new infinite group
Run: Go outside and give the teacher its eleven-hole box: everybody doubles, the gold guests take the odd cottages, and it reads “Done” out.
Change and predict: Why does it wait for the bell before letting the newcomers in? Predict where the gold guests would end up if it did not.
A robot solves Resort Infinity 4: teaches ×4 to the mover and 4i − j to the clerk — a copy of the group wearing a minus sign — and lets three groups in.
Needs The resort teacher, problem 3Resort Infinity 4: three infinite groups
Run: Go outside and give the teacher its box: everybody moves to four times their address, and green, plum and teal fill three cottages in every four.
Change and predict: Read the clerk it taught: which step is the minus sign? Predict what the clerk would do to plum guest 2 without it.
A robot solves Resort Infinity 5: teaches the mover and, since a lesson trains one robot and the clerk is a team on a scale, hands the growing-squares team over ready-made — and says so.
Needs The resort teacher, problem 4Resort Infinity 5: infinitely many groups
Run: Go outside and give the teacher its box: everybody doubles, the pairs (i, j) are numbered by growing squares, and rose, lime and brown take the odd cottages.
Change and predict: Could a teacher teach a team? Predict what the lesson would have to do that this one cannot.