WaLua - Lua web assembly builder

This script compiles a Web Assembly version of lua.

It downloads the lua sources and Emscripten utilities from the git repositories. However it still depends on some system installed software: python, cmake and posix shell and utilities.

You can try the on-line version.

Build

To build using the software from your os use:

./walua.sh make

Note that emsdk is still downloaded and any other system-wide installation is ignored. This method requires python, git and cmake installed on your machine.

To build using a container, use:

docker build -t walua .
docker run --rm -v "$PWD:/DATA" walua

This method requires docker installed and running on your machine.

The build script generates a walua_build subfolder in the current directory containing all the files needed to run the PUC-Rio lua VM in a browser. Most of the files and sub-folders are just needed at build time. The only release files are: walua.js and walua.wasm. The walua.merged.js contains an amalgamation of both walua.js and walua.wasm that can be used as a single file release.

Usage

To use walua, you just have to load walua.js from a html page, the walua.wasm will be automatically loaded by it. It will expose the following global function:

• compile_lua - It accept a string and compile it as lua chunk. It returns 0 if all is right, or -1 if there is an error. In such case, it also write some information on the standard error (descripted in the following)
• step_lua - It performs an execution step. It returns 0 if no other step are needed, 1 otherwise. By default all the script previously passed to the compile_lua function is executed in one step, so it always returns 0.

The following global function are used if defined:

• append_output is called everytime lua wants to write to the standard output. If undefined, console.log is used.
• append_error is called everytime lua wants to write to the standard error. If undefined, console.log is used.

The compile_lua and step_lua can be redefined by your lua code. The functions just calls the lua functions stored in the WALUA_COMPILE and WALUA_STEP globals. So, for example, the following javascript code:

compile_lua("WALUA_COMPILE = function() error('compilation disabled') end")

will disable any further compilation.

The defult compiler and runner are kept simple by purpose: it supposes that you will write one suitable to your application. A simple exaple Is in playground.html. More complex ones can be found int the Client-side tools project, e.g. Lua playground.

Example

In the playground.html there is a little usage example. The one in the root directory is just a template, a runnable amalgamation can be found in the distribution directory. It can be run directly from the disk without a proper web server.

This example just run a lua code snipeet at startup, showing its stdout/stderr. You can easly change the snippet: it is at end of the html file, in the <script> tag with id startup_code.

So... just click on playground.html to let the browser run the lua code!