# WAG - The WebAssembly Code Generator

This Ruby gem allows you to generate WebAssembly programs programmatically using
a DSL.

It is closely modeled after WAT, the WebAssembly text format, and at this stage
generates WAT and compiles and validates it using [the WebAssembly Binary Toolkit][1].

Due to the flexibility of WAT this library is very flexible in what structures
it allows you to create. Be aware that you can build modules which are not
valid WASM. Always validate your modules by using `#to_wasm.valid?`.

## Keyword conflict

Any WASM instructions whose name conflicts with a Ruby keyword (eg `loop`,
`return`, etc) are also aliased with a underscore suffix for use in the DSL. The
methods defining the original names are also there, so can be used by the likes
of `public_send`, etc.

## Folding

WAG supports generating both the "folded" and "unfolded" variants of the WAT
language. As an example here are two implementations of Euclid's Greatest
Common Divisor algorithm:

### Example of unfolded generation

```ruby
unfolded = WAG::Module.new.build do
  func(:gcd) do
    param(:a, :i32)
    param(:b, :i32)
    result(:i32)
    local(:r, :i32)

    block
    loop_

    # let r = a % b
    local.get(:a)
    local.get(:b)
    i32.rem_s
    local.set(:r)

    # let a = b and b = R
    local.get(:b)
    local.set(:a)
    local.get(:r)
    local.set(:b)


    # if a % b == 0, return b
    local.get(:a)
    local.get(:b)
    i32.rem_s
    i32.eqz
    br_if 1

    br 0
    end_
    end_

    local.get(:b)
    return_
  end
  export("gcd").func(:gcd)
end
```

### Example of folded generation

```ruby
folded = WAG::Module.new.build do
  func(:gcd) do
    param(:a, :i32)
    param(:b, :i32)
    result(:i32)

    local(:r, :i32)

    block do
      loop_ do
        # let r = a % b
        local.set(:r) do
          i32.rem_s do
            local.get(:a)
            local.get(:b)
          end
        end

        # let a = b and b = R
        local.set(:a) do
          local.get(:b)
        end
        local.set(:b) do
          local.get(:r)
        end

        # if a % b == 0, return b
        br_if(1) do
          i32.eqz do
            i32.rem_s do
              local.get(:a)
              local.get(:b)
            end
          end
        end

        br 0
      end
    end

    return_ do
      local.get(:b)
    end
  end
  export("gcd") do
    func(:gcd)
  end
end
```

Both modules emit identical WASM bytecode and produce the same answers:

```ruby
folded.to_wasm.save("folded.wasm")
unfolded.to_wasm.save("unfolded.wasm")
```

```bash
$ sha256sum folded.wasm unfolded.wasm
0023ef97eba001226401e432912f2e644a6cbef107ba183546c51177eee46e2c  folded.wasm
0023ef97eba001226401e432912f2e644a6cbef107ba183546c51177eee46e2c  unfolded.wasm
$ wasmtime folded.wasm --invoke gcd 270 192
6
$ wasmtime unfolded.wasm --invoke gcd 270 192
6
```

1: https://github.com/WebAssembly/wabt

## Installation

Add this line to your application's `Gemfile`:

```ruby
gem 'wag'
```

And then execute:

    $ bundle install

Or install it yourself as:

    $ gem install wag

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome at https://harton.dev/james/wag.

## License

This software is licensed under the terms of the
[HL3-FULL](https://firstdonoharm.dev), see the `LICENSE.md` file included with
this package for the terms.

This license actively proscribes this software being used by and for some
industries, countries and activities. If your usage of this software doesn't
comply with the terms of this license, then [contact me](mailto:james@harton.nz)
with the details of your use-case to organise the purchase of a license - the
cost of which may include a donation to a suitable charity or NGO.