Metalua Manual

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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 everything-is-a-table approach.
  • 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 mlp.
    • 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 faster.
    • 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 including yours.
    A whole category of metalua users, who want to use third party libraries rather than reinventing their own wheels, will be primarily interested by these.
    • metalua.runtime: extensions to Lua core libraries: base, table, string.
    • 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 source files.
    • 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 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.

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