WebAssembly - Text Format: A Beginner's Guide

Hello there, future coding superstar! Today, we're going to embark on an exciting journey into the world of WebAssembly's Text Format, affectionately known as WAT. Don't worry if you've never coded before – we'll start from the very beginning and work our way up together. By the end of this tutorial, you'll be WAT-ting like a pro! (See what I did there? ?)

What is WebAssembly Text Format (WAT)?

Before we dive into the nitty-gritty, let's understand what WAT actually is. WebAssembly Text Format is a human-readable representation of WebAssembly binary code. It's like the friendly, approachable cousin of the more intimidating binary format. WAT allows us to write and read WebAssembly code in a text format, making it easier for humans like us to understand and work with.

Why Learn WAT?

You might be wondering, "Why should I bother learning WAT?" Well, my curious friend, WAT is an excellent way to understand how WebAssembly works under the hood. It's like learning to read sheet music before playing an instrument – it gives you a deeper appreciation and understanding of the craft.

WAT Code Basics

Let's start with the basics of WAT code. Don't worry; we'll take it step by step, and before you know it, you'll be writing your own WAT code!

Module Structure

Every WAT program starts with a module. Think of a module as a container for all your code. Here's what it looks like:

(module
  ;; Your code goes here
)

This is like saying, "Hey, computer! I'm about to give you some instructions, so pay attention!"

Functions

Functions are the building blocks of our WAT code. They're like little machines that do specific tasks. Let's create a simple function that adds two numbers:

(module
  (func $add (param $a i32) (param $b i32) (result i32)
    local.get $a
    local.get $b
    i32.add
  )
)

Let's break this down:

1. (func $add ...: This declares a function named "add".
2. (param $a i32) (param $b i32): These are our input parameters. We're saying we expect two 32-bit integers.
3. (result i32): This specifies that our function will return a 32-bit integer.
4. local.get $a and local.get $b: These lines retrieve our input parameters.
5. i32.add: This performs the addition operation.

Exporting Functions

Now, we've created a function, but it's like a hidden treasure – no one outside our module can use it! Let's fix that by exporting our function:

(module
  (func $add (param $a i32) (param $b i32) (result i32)
    local.get $a
    local.get $b
    i32.add
  )
  (export "add" (func $add))
)

The (export "add" (func $add)) line makes our add function available to the outside world. It's like putting a "OPEN" sign on our little addition machine!

More Complex Operations

Now that we've got the basics down, let's try something a bit more challenging. How about a function that calculates the factorial of a number?

(module
  (func $factorial (param $n i32) (result i32)
    (local $result i32)
    (local $i i32)

    i32.const 1
    local.set $result

    i32.const 1
    local.set $i

    (loop $continue
      local.get $i
      local.get $n
      i32.gt_u
      if
        local.get $result
        return
      end

      local.get $result
      local.get $i
      i32.mul
      local.set $result

      local.get $i
      i32.const 1
      i32.add
      local.set $i

      br $continue
    )

    local.get $result
  )
  (export "factorial" (func $factorial))
)

Wow, that's a mouthful! Let's break it down:

1. We declare our function with one parameter $n and two local variables $result and $i.
2. We initialize $result to 1 and $i to 1.
3. We start a loop that continues until $i is greater than $n.
4. In each iteration, we multiply $result by $i and increment $i.
5. Once the loop is done, we return $result.

This function calculates the factorial of the input number. For example, if we input 5, it will calculate 5 4 3 2 1 = 120.

WAT Methods Table

Here's a table of some common WAT methods we've used and a few more:

Method	Description
i32.add	Adds two 32-bit integers
i32.sub	Subtracts two 32-bit integers
i32.mul	Multiplies two 32-bit integers
i32.div_s	Divides two 32-bit integers (signed)
i32.const	Declares a constant 32-bit integer
local.get	Retrieves a local variable
local.set	Sets a local variable
i32.gt_u	Unsigned greater than comparison
if	Starts an if statement
loop	Starts a loop
br	Branch (jump) to a specific point

Conclusion

And there you have it, my coding apprentice! You've just taken your first steps into the world of WebAssembly Text Format. We've covered the basics of modules, functions, exporting, and even tackled a more complex factorial function. Remember, learning to code is like learning a new language – it takes practice and patience. But with each line of WAT you write, you're getting closer to becoming a WebAssembly wizard!

Keep experimenting, keep learning, and most importantly, keep having fun with WAT. Before you know it, you'll be writing complex algorithms and impressing all your friends with your WebAssembly skills. Happy coding!

Credits: Image by storyset