path: root/2022/captions/emacsconf-2022-asmblox--asmblox-a-game-based-on-webassembly-that-no-one-asked-for--zachary-romero--main.vtt

WEBVTT captioned by sachac

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Hi, I'm Zach and today I'll be giving

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a presentation on asm-blox,

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a programming game inspired by WebAssembly.

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So programming games came into prominence

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about a decade ago and are loved for providing

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interesting programming challenges

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without all the messiness of real world programming.

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I wanted to make a programming game

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and I decided to base it off of TIS-100,

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having a pretty basic UI.

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It seemed pretty doable in Emacs.

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TIS 100 is a programming game

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where you write a fictional assembly language

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into a grid of cells which can each

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communicate with one another,

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you're tasked with solving

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fairly simple CS 101 like problems.

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To mix things up a bit I decided to base

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the language of asm-blox off of

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WebAssembly, which is stack based,

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as opposed to TIS-100 which is registered based.

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Here you can see the same program

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written in the game TIS-100,

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what it looks like in asm-blox,

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and the original WebAssembly that it's based off of.

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With that said, let's get into a demo.

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This is the game board.

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It's a 4 by 3 grid.

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Each cell has a stack of size 4.

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First off, I'll show some of the stack editing commands.

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We can add a value with the const function.

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Here we're adding two values to this stack

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to get added, and eventually the stack gets overflowed.

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We can fix that as follows with the clear command,

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so that clears the stack.

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We can duplicate values on the stack.

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This duplicates the item at the bottom of the stack.

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10 gets put on, 20 gets put on,

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then 10 will get duplicated

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and put on the top of the stack.

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We can increment. For example, this increments

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the second to bottom, the second to bottom

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from the stack.

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So 10, 20, increment that, clear.

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That's basic stack operations.

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Next up, we have numeric commands.

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For example, here, if we add "add",

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it pops two values off the stack,

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adds them, and pushes the result on.

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Another way we can write this is as follows.

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We can have the add here

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and then nest the two constants,

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and then this does the same thing.

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First, the inner constant operations run,

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and then the outer add operation runs.

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We can nest as deeply as we want.

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There's also subtraction, multiplication, and whatnot.

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Next up are Boolean operations.

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Zero counts as true.

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Anything else--sorry, zero counts as false.

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Anything else is true.

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For example, this would give us false and true,

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so that result should be false.

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Zero gets put on the stack,

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one gets put on, and then the "and" operation.

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So there's also or, not,

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and various numerical comparison operations

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like greater than and less than.

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Next up are the port operations.

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We can send values to other cells as follows.

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Here we create a value

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and then send it right.

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Let's run this.

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The 10 goes on the stack,

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and then it gets sent to the right.

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Here it's waiting for this cell to pick it up.

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It can pick it up just as follows.

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So left... and then why don't we have it

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drop that value after it gets it.

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So the 10 gets sent to the right.

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This one picks it up and drops it.

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Lastly, we have control flow,

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which is a bit tricky,

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but with this visual,

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it helps explain it.

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There are two block constructs, "block" and "loop",

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and there's two jumping constructs, "br" and "brif".

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So if "loop" is jumped to,

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the control flow goes to the beginning,

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the top of the loop.

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If a block is jumped to,

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it goes to the end of the block,

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and these various blocks

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are identified by their level of nestedness.

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From the point of view of this jump statement,

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this "br" statement, this is block level 0,

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this is 1, this is 2.

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So here, "br 1" would be referring to this loop.

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What this [br 1] would do is,

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it would jump to this loop right here.

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If we were to do this [br 2], what this would do is,

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this would jump past this block right here.

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So as another example, this right here,

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this is a loop that generates increasing numbers.

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Let's see. Next up, we have modules.

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This is an example of a stack module.

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In addition to stack, there's also heaps.

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What this does is it allows us to create

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an extra stack that we can push and pop items onto.

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This one can have as large size as we need.

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Here it has a size of 20.

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It's taking values from up

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and exposing those values on the left.

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This loop right here, it generates numbers,

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and it's putting them onto the stack.

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We can see here that those numbers

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are being exposed to this cell right here.

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It's just taking values, and eventually,

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it's going to overflow and cause an error.

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That finishes the basic commands.

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Why don't we try solving this puzzle.

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The puzzle description is right here.

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We want to read a value from I.

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Send 1 to G if I is greater than 0.

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Send 1 to E if it's equal to 0.

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Send 1 to L if it's less than 0.

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And then all the other ones, we send 0 to.

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First things first, let's send the value we get

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from the input down as follows.

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Let's send that value right.

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You get from up.

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Okay. So next, we're getting a value on the left.

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Now we want to compare if this number is greater than 0.

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If it's greater than 0, we send 1 to G.

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Let's perform the greater than operation

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on that item we just got, and we're comparing it to 0.

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Now that result, we're going to send down,

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and we're going to send this original value

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we got from here to the right.

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Here, we do a similar step.

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We get the value from the left,

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but this time, we have to do an equal operation.

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Is that number we got equal to 0?

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We send that result down,

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and then send this number to the right.

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Lastly, we get this number from the left.

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Here, we need to compare if it's less than 0.

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We send that result down,

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and now lastly, we drop that remaining value.

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Okay, let's--oh, and then lastly,

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we need to send down the value we get up.

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Send down, up, send down, up.

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Okay, so let's try running this.

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Let's see. We notice that

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the numbers are coming in from I.

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They're going through our various conditions

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and should be sending all the correct values.

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It looks like we're not getting any errors so far.

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Let's speed this up.

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That completes the puzzle.

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Now let's get into some of the implementation details.

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The first thing is the game loop.

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The game loop is... So this is actually extremely simple.

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All the state for the entire game

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is stored in just a few variables.

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There's one variable storing

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the text of each cell as a vector of strings.

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There's a single function

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that renders the entire game, the entire board.

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There's a single function that would render

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this entire screen based off of the state,

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and then the game waits for you to press a key.

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The key usually, depending on what action you perform,

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updates the state and causes a re-render.

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It's an extremely simple game loop,

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but it makes implementing it pretty easy.

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To demonstrate how this game loop works,

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I have a simple demo prepared.

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This is a game of tic-tac-toe.

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Let me show this real fast.

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It's an extremely simple implementation,

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but it follows the same principles

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that I used in asm-blox.

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First, we have the state defined in variables.

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Here we have two pieces of state.

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We have which player's turn it is

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and the state of the game board.

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The player turn can be nil if it's empty,

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the string "x" or the string "o".

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Then the game board is a list of nine board elements.

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So that's the state.

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Then we have a helper function.

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You can go into the details,

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but it just returns true

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if the board has a winning player.

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Part two is the rendering function.

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Only based off of the game state,

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we have a function that erases the buffer

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and draws this from scratch.

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That's this part right here.

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Lastly, we have the action.

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We have one action which is bound to RET,

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and it places a player token.

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Once it places a player token,

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it rerenders the board,

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and all the rerendering is handled by this function.

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Then we have just creating of the mode

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and initialization function.

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With these three steps

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it clearly separates out all of the state,

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the rendering, and the actions,

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and it makes implementing it very simple.

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One trick that's used here and that I use

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in my asm-blox game is that

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when I render the board,

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I propertize the text to contain extra information.

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For example, here, each cell has

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a tic-tac-toe index to indicate which number cell it is.

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This has index 0, 1, 2, all the way up to 8.

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That way, for placing, the only thing it has to do

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is just look at its position

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based off of the text property.

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It makes implementation extremely simple.

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Next up, we have the implementation of the code cells.

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If you notice, here it's kind of weird

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how it's like a buffer, but each cell kind of acts

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like its own buffer, and it has its own limits.

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All of the Emacs editing--

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well, some of the Emacs editing commands kind of work,

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like beginning-of-line, end-of-line, end-of-buffer.

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How is that done?

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Well, it's all just a trick, actually.

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Each cell has text properties of which line it's at

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and its cell coordinates.

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Whenever a key is pressed for editing, moving lines--

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there's even kind of more complicated things

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like switching cells around--

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so all of that,

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it knows which position it's in,

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it knows what cell it's in,

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and then it copies the text of the cell,

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because remember, the contents of the cell

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are stored in internal state.

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It copies that cell contents into a temporary buffer.

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It then moves the point to whichever line it was

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in the game board.

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It performs the action.

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It makes sure that the resulting text isn't

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longer than the cell width or the cell height.

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If everything checks out,

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it updates the state and calls a re-render.

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So there's nothing going on in here

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that's, like, actually inserting a letter A.

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It's all updating the state and causing a re-render.

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So this makes things like certain

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internal Emacs editing constructs

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pretty hard to use, like undoing.

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Normally the undoing construct

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works off the contents of the buffer.

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But if your buffer is actually just

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a reflection of the internal state,

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then how does undoing work?

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Well, it pretty much is kind of a hack.

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I mean, undoing is here,

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but it's pretty much redone

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in a not so configurable, not so modifiable way.

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Pretty much everything is like that,

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from these parentheses highlighting...

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Normally, parentheses highlighting

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would be kind of weird,

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with cross-line parentheses and everything.

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All of that had to be redone.

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Another point about how this is implemented

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is the assembly text to executable code.

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If you're familiar with WebAssembly

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you might have encountered a tool wat-wasm.

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It basically converts the WebAssembly text format

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to byte code.

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And what I do here... It goes through a similar process.

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Normally, when you're writing this text format,

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you can nest things as deeply as you want.

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Basically, what happens is it flattens out everything.

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It kind of knows the order

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that all these things are going to get executed,

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and then it puts it into one single line

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that it can just run through and execute.

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The same thing for the loops and blocks.

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It internally generates labels and jump statements.

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So that concludes this presentation.

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Thank you for listening,

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and I hope you enjoy the rest of the conference.