TITLE

Status of Lua on Parrot

Introduction

Lua is an extension programming language designed to support general procedural programming with data description facilities. It also offers good support for object-oriented programming, functional programming, and data-driven programming. Lua is intended to be used as a powerful, light-weight scripting language for any program that needs one.

The homepage is http://www.lua.org/.

The reference manual is available on http://www.lua.org/manual/.

This implementation is aligned with Lua 5.1 specifications.

PIR Compiler/Interpreter

lua.pbc is the interpreter/compiler, see languages/lua/src/lua51.pir & languages/lua/lua.pir.

lua.pbc is written in PIR and generates PIR from Lua sources. lua.pbc uses the following Parrot compiler toolchain components :

PGE

The Lua grammar is described in languages/lua/src/lua51.pg.

The PIR code is emitted by CodeString.

PGE is also used by the Lua pattern compiler in languages/lua/lib/luaregex.pir.

TGE

Two stages of tree transformation are used languages/lua/src/PASTGrammar.tg & languages/lua/src/POSTGrammar.tg.

PAST-pm

The AST is represented with compilers/past-pm/PAST/Node.pir and the OST with compilers/past-pm/POST/Node.pir.

HLLCompiler

This Lua compiler extends the base class runtime/parrot/library/Parrot/HLLCompiler.pir.

The lexicography part could be checked with languages/lua/test_lex.pir.

The code generation could be examined with languages/lua/luap.pir.

KNOWN PROBLEMS

in languages/lua/t/closure.t :

    a = {}
    local x = 20
    for i=1,10 do
        local y = 0
        a[i] = function () y=y+1; return x+y end
    end

    print(a[1]())
    print(a[1]())
    print(a[2]())

    --[[
    The loop creates ten closures (that is, ten instances of the anonymous
    function). Each of these closures uses a different y variable, while all
    of them share the same x.
    ]]

y variable is not different.

Perl Compiler (deprecated)

This compiler is written in Perl5 :

• lexer

Implemented with Perl5 regex

languages/lua/Lua/lexer.pm

• parser

Implemented with Parse::Yapp.

It supports the full grammar described in languages/lua/doc/lua51.bnf.

Only one error rule, so the syntax error diagnostic is minimalist.

languages/lua/Lua/lua51.yp

• code generation

languages/lua/Lua/build.pm

• symbole table

languages/lua/Lua/symbtab.pm

• opcode representation

languages/lua/Lua/opcode.pm

• opcode emission

languages/lua/Lua/pir.pm

Lua Types

There are eight basic types in Lua, each of them is implemented by a PMC.

• nil languages/lua/pmc/luanil.pmc
• boolean languages/lua/pmc/luaboolean.pmc
• number languages/lua/pmc/luanumber.pmc
• string languages/lua/pmc/luastring.pmc
• function languages/lua/pmc/luafunction.pmc & languages/lua/pmc/luaclosure.pmc
• userdata languages/lua/pmc/luauserdata.pmc

This type allows OO extension.

Currently, file in I/O library is an userdata.

• thread languages/lua/pmc/luathread.pmc

This type is used to implement coroutines. The current implementation use the library runtime/parrot/library/Parrot/Coroutine.pir.

• table languages/lua/pmc/luatable.pmc

This type is the data structure of the language.

languages/lua/pmc/luaany.pmc provides an abstract base class for all Lua types.

languages/lua/pmc/lua.pmc is a singleton PMC what holds some static methods.

BUGS

Lua PMC have problems with the Parrot garbage collector : used objects are released by the GC (infant mortality ?).

So, use the option --no-gc.

TODO

Arguments passing in invoke method of table. Where are there ?

Weak table, weak reference.

IMPROVEMENT

table with a mixed array and hash (and with an efficient next method).

Lua Standard Libraries

Lua 5.1 defines the following standard libraries:

• basic library languages/lua/lib/luabasic.pir
• coroutine manipulation languages/lua/lib/luacoroutine.pir
• package library languages/lua/lib/luapackage.pir
• string manipulation languages/lua/lib/luastring.pir
• table manipulation languages/lua/lib/luatable.pir
• mathematical functions languages/lua/lib/luamath.pir
• input and output languages/lua/lib/luaio.pir, languages/lua/lib/luafile.pir
• operating system facilities languages/lua/lib/luaos.pir
• debug facilities languages/lua/lib/luadebug.pir

languages/lua/lib/luaaux.pir is the equivalent of Auxiliary Library.

languages/lua/lib/luaregex.pir implements a regex compiler using PGE.

TODO

Except math & table libraries, all of these libraries are incomplete.

IMPROVEMENT

As compiled regex are not stored in Lua variable, the Regex compiler needs a Memoization mecanism (well-known optimization).

Extension Libraries

These libraries are loaded dynamically with the Lua function require.

• alarm library languages/lua/lib/alarm.pir
• Lua File System library languages/lua/lib/lfs.pir

Next Milestones

Debugging & stabilisation.

Add a Lua bytecode translator as a package loader.

Related Projects

Klaas-Jan Stol works on 2 projects :

• Monkey, an implementation of Lua on Parrot

A Lua to PIR compiler implemented in C

• lua2pir

A Lua bytecode to PIR compiler

See http://kjs.home.fmf.nl/.

AUTHOR

Francois Perrad.