Hello, I have been thinking about writing a Lua to JavaScript translator.
The main use case would simply be to provide an alternative language for
the web. You would just have to run the translator before you use the
script.
This would be different than the lua2js which already exists on LuaForge
since I would want to make it work in all cases with the only restrictions
being on what modules can be used. I think lua2js only does a superficial
translation. For example, I don't think it handles using functions as an
index into a table.
I do not have a goal of making the output readable. In fact I might
purposely obfuscate the output to hinder reverse-engineering efforts of
the translated code.
The approach that seems the easiest to me is to run the Lua source through
luac.exe and use the output of luac as the input of the translator. This
way I don't have to worry about lexing or parsing. I also could have a
smaller range of inputs to worry about; there would only be the 38 types
of instructions to translate. The down-side to this approach is that the
format of the luac output could change significantly between versions.
Now for my questions:
Is this already being work on?
Can you think of any major problems that would prevent the approach
described in the previous paragraph from working?
Can you think of a better approach?
Thanks,
Phil
P.S. I couldn't find a search feature for the mailing list archive; so
sorry if this has already been discussed.

wiki

lua2c is a Lua module and utility to convert Lua 5.1 source code to C API code.

Translate.lua translate.lua Table of contents. Data options Translator options Tokenizer options Cuda options HookManager options Logger options Other options tag.lua lm.lua tools/buildvocab.lua tools/releasemodel.lua tools/tokenize.lua tools/learnbpe.lua tools/translationserver.lua. Converter c code to python code. History folderopen save clouddownload deleteoutline contentcopy openinfull. Paste or type your data here. Code to translate: Input language: Output language: Download file Switch languages. Universal Transpiler Code to translate: Input language: Output language: Download file Switch languages.

Description

This utility converts a given Lua source file into an equivalent C source file written in terms of Lua C API calls. At least, this works for a large subset of the Lua language (see limitations below).

The compiler is written entirely in Lua, and no build/install is needed. This project reuses Metalua's gg/mlp parser to convert Lua source to a Metalua-style [1] AST over which the compiler then operates. lua2c does not require Metalua itself though since gg/mlp is bundled in the distribution (patched metalua-0.4.1-rc1) and is written in pure Lua.

Usage

Example usage:

which generates a C file similar to as shown here: [bisect.c].

You may also use the shell script 'clua' to compile Lua->C->machine code and execute all in one step. However, you may need to edit the variables in the file to match your system since this utility invokes the C compiler.

lua2c can even compile itself! (Note: the -c option compiles only without running.)

Related Work

luac2c - This related effort by Hisham Muhammad [2] converts Lua bytecodes to C source, whereas this project converts Lua source to C source. luac2c runs into a few similar limitations as given below. luac2c has remained experimental but superseded Luiz Henrique De Figueiredo's very basic but similarly named lua2c for Lua 4.0 [3].

luagen++ [4] uses C++ expression templates to translate Lua-like C++ statements to C API calls. Some of the code generation structure is actually fairly similar to lua2c.

Python Pyrex [5] does something similar in Python but has the added goal of lowering the boundary between C and Python code. Something like that could be done with lua2c, especially since lua2c uses the extensible gg parser.

Clue by David Given [6] does the opposite: convert C source to Lua source.

luac + BinToCee [10] allow compilation of Lua source to bytecodes and/or embedding in a C file.

LuaInterpreterInLua [12] - is the Lua interpreter (lua.c) reimplemented in Lua. It can be compiled to C via lua2c (e.g. for scaffolding).

Potential Uses

I think this project not only is theoretically nice to have but has a number of potential uses:

Provide another approach of compiling Lua to machine code (rather than luac + BinToCee).
Streamline the interface between C and Lua code and allow efficient access to C datatypes from Lua (see Pyrex above).
Compile Lua to optimized C. For example, by statically determining that certain variables are used in a restricted way (e.g. by decorating the Lua source file with pragmas or determining this implicitly by inference), certain code constructs might be simplified to use plain C rather that the Lua C API. This could allow certain Lua code written with sufficient care to run at native speeds. Since it compiles to C, it will even work on CPUs where LuaJIT is not available.

Limitations

WARNING: This code passes much of the Lua 5.1 test suite [7] and can compile itself, but the code is new and there can still be errors. In particular, a few language features (e.g. coroutines) are not implemented. See comments in lua2c.lua for details. Please report bugs/patches on the wiki.

lua2c does not currently support coroutines, functions that normally reject C functions (e.g. setfenv), and possibly tail call optimizations. Not all of these have the exact analogue in C. Coroutines might not ever be supported. However, some solutions might be explored [8][9], including possibly generating code that maintains the coroutine context in Lua tables.

Closures and upvalues are implemented, but creating and accessing upvalues is somewhat slow due to the implementation (see implementation notes below) and hopefully can be improved.

Now that the code is fairly complete/robust, more attention can be given to optimizing the code generation. Performance was 25%-75% of regular Lua when running a few tests [11], but hopefully future optimizations will improve that.

Lua 5.2 Notes

LuaFiveTwo (as of 5.2.0-work4) deprecates getfenv and setfenv, which eliminates one of the limitations above.
LuaFiveTwo has new lua_arith and lua_compare C API functions, which eliminate the need for lua2c to reimplement these functions.
LuaFiveTwo also has new lua_yieldk, lua_callk, and lua_pcallk functions for coroutines and might help to implement coroutines in lua2c.
lua2c might implement upvalues as C function upvalues rather than tables, given LuaFiveTwo implements lua_upvaluejoin/lua_setupvalue/lua_setupvalue, so C functions can share upvalues directly.
Concerning tail calls, see [1].

Download

Latest development source (recommended): http://github.com/davidm/lua2c/ . From here you can browse the source, download a tar/zip snapshot, or checkout with git by running 'git clone git://github.com/davidm/lua2c.git'.
Last release distribution: [lua2c-0.2.1-20080802.tar.gz]; Older versions: [achive]

Project Page

The project page is currently http://lua-users.org/wiki/LuaToCee .

Author

Licensing

Implementation Notes

Some implementation notes will likely go here.

Important topics include

Implementing closures with upvalues in C. The current approach is to store local variables that are used as upvalues in a Lua table scoped to the block (lc_newclosuretable). Utility functions lc_getupvalue/lc_setupvalue access it.
Supporting vararg (...) functions. Mainly, this just requires allowing the stack to be shifted by an arbitrary amount (lc_nextra).
The transformation process: Lua code string -> Lua AST -> C AST -> C code string
Implementation of uti

Lua C++ Translator