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.

Compiler

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

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.

TODO

Handle arguments from command line.

Try to use Parse::RecDescent (the original Lua uses a LL parser).

Lua PMC

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
• 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.

• table languages/lua/pmc/luatable.pmc

This type is the data structure of the language.

languages/lua/pmc/luabase.pmc provides an abstract base class for some Lua types (nil, boolean, number, string, table).

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.

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
• 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.

TODO

Except math library, all of these libraries are incomplete.

And the coroutine library does not work.

KNOWN PROBLEMS

Currently, these libraries are included as PIR file (not loaded as bytecode PBC) because HLL support for Sub/Closure is incomplete with PBC.

Next Milestones

Understand how work PGE & TGE and write an interpreter in PIR.

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://members.home.nl/joeijoei/.

AUTHOR

Francois Perrad.