This manual tries to be as comprehensive as possible; however, you don't
necessarily have to read all of it before starting to do interesting stuff with
metalua. Here's a brief summary of what the different parts of the manual
address, and why you might want to read them immediately---or not.
Before reading this manual: metalua is based on Lua, so
you'll need a minimal level of Lua proficiency. You can probably get
away without knowing much about metatables, environments or
coroutines, but you need to be at ease with basic flow control,
scoping rules, first-class functions, and the whole
- Meta-programming in metalua: this chapter exposes the generic principles
of static meta-programming: meta-levels in sources, AST representation of
code, meta-operators. You need to read this carefully if you plan to write any
non-trivial meta-programming code and you've never used languages like, Common
Lisp, camlp4 or Converge. If you're familiar with one of these, a cursory look
over this chapter might be enough for you.
- Standard meta-programming libraries: these are the tools that will allow
you to manipulate code effectively; the more advanced an extension you want to
write the more of these you'll want to know.
mlp is the dynamically extensible metalua parser. You need to know it
if you want to change or extend the language's syntax
- gg is the grammar generator, the library which lets you manipulate
dynamic parsers. You need to know it in order to do anything useful with
- match is an extension supporting structural pattern matching (which has
almost nothing to do with regular expressions on strings). It's a construct
taken from the ML language familly, which lets you manipulate advanced data
structures in vrey powerful ways. It's extremely helpful, among others, when
working with AST, i.e. for most interesting meta-programs.
- walk is a code walker generator: smomething akin to a visitor pattern,
which will help you to write code analysers or transformers. Whenever you
want to find and transform all return statements in an AST, rename some
conflicting local variables, check for the presence of nested for loops
etc., you'll have to write a code walker, and walk will get you there much
- hygiene offers hygienic macros, i.e. protects you from accidental
variable captures. As opposed to e.g. Scheme, macro writing is not limited
to a term rewriting system in metalua, which lets more power to the
programmer, but prevents from completely automating macro hygienization. If
you wrote an extension and you want to raise it to production-quality,
you'll need among others to protect its users from variable captures, and
you'll need to hygienize it. If you don't feel like cluttering your code
with dozens of gensym calls, you'll want to use the macro hygienizer.
- dollar: if you wrote a macro, but don't feel the need to give it a
dedicated syntax extension, this library will let you call this macro as a
regular function call, except that it will be prefixed with a ``$''.
- General purpose libraries: Lua strives at staying minimalist, and does
not come with batteries included; you're expected to grab them separately,
currently from luaforge, and eventually from a Lua Rocks repository. Metalua
needs quite some support to run, and relies on a number of imported and
custom-built libraries. Most of them can be reused for many other purposes
A whole category of metalua users, who want to use third party libraries
rather than reinventing their own wheels, will be primarily interested by
metalua.runtime: extensions to Lua core libraries: base, table,
- metalua.compiler: mlc offers a consistent interface to metalua
compilation and code representation transformers. 'package', 'loadstring',
'dostring', 'loadfile' and 'dofile' are also updated to handle metalua
- clopts simplifies and unifies the handling of command line options
for metalua programs.
- springs brings together Lua Ring's handling of separate Lua universes
with Pluto's communication capabilities.
- clist offers an extended tables-as-list interface: lists by
comprehension à la Haskell or Python, list chunks etc.
- xglobal makes global variables declaration mandatory, for safer
programming, with almost no runtime overhead, and a syntax consistant qith
local variables declaration.
- anaphoric introduces anaphoric control structures, akin to Common
Lisp's aif-familly macros.
- trycatch provides a proper exception system, with reliable finally
blocks and exception catching by structural pattern matching.
- log eases the terminal logging of variables, mainly for those from
the Printf-based School of Debugging.
- types offers dynamic type checking to metalua programs. It supports
variable typing as opposed to value typing, and advanced type system
features (polymorphism, dependant types etc.).
- Examples and tutorials: this chapter lists a series of tiny
meta-programs whose main purpose is didactic, and walks through the detailed
implementation of a couple of non-trivial extensions.