Luax Design Document

• opcode explanation
• luax syntax BNF
• source code structure
• test luax code
  • opcode generator test
  • Virtual Machine test

syntax parser

• Luax syntax BNF

Luax uses a simple token scanner and recursive descent parser. These codes are located at parser.c. These functions of every nonterminal symbols are named the same as BNF.txt, which makes it easy to view the whole code. When parser find one rule, it would call the callback function of this rule. These callback functions are located at parser_callback.c.

opcode explanation and opcode generator

• opcode explanation

VM

(namespace)environment

environment table's meta functions

garbage collection

run-time environment

luax complier translate luax code to one kind of middle code, we call it opcode. luax virtual machine run commands in opcode one by one. The luax statement is runed in a default function, created by the VM. It's very important to know that every luax statement runs in a luax function. A function has these things hanged on it:

• a table object used to store local variable
• a table reference used to link to it's father environment When a function was created, it store it's current environment as it's father environment. Every time this function was called, it created a table used to store it's local variable, and in the same time, we can access it's father environment(these variables when it was created). We use this to achieve closure.

sequence in stack

forward: first one first in. For example, func(1, 2) => push 1; push 2 reverse:

        situation               |   type  |   explain

------------------------------------|---------|------------------------------------------------------------ func(1, 2) | reverse | return 1, 2 | reverse | func = function() return 1, 2; end; local a, b = func(); local a, b | reverse | local a, b = 1, 2, 3 | reverse |