meta_compile

A meta compilation framework for Ruby à la Meta-II by Val Schorre.

This uses a C version of Meta-II developed by Long Nguyen to bootstrap a Ruby version from a fully self-contained, 26 (non-empty) line specification file. The generated Ruby Meta-II compiler file is 231 lines of Ruby code.

Install

Clone the git repo and then run:

    rake bootstrap

and it will bootstrap and print info about each step. This requires gcc, rake and a recent ruby.

If you only want the finished result you can just install as a gem:

    gem install meta_compile

since it is available on rubygems.org.

Manually verifying that it is a meta compiler

In your local copy of the git repo, use the pre-generated binary to compile the specification file to a ruby file:

    bin/meta_compile syntaxes/meta_to_ruby_minimal.meta > t.rb

This generates a t.rb which is itself a compiler for meta syntax specs. So lets use it to generate itself:

    ruby t.rb syntaxes/meta_to_ruby_minimal.meta > t2.rb

And ensure they are really the same:

    diff t.rb t2.rb

To be really sure we can try the generated t2.rb as a meta-compiler:

    ruby t2.rb syntaxes/meta_to_ruby_minimal.meta > t3.rb

and this should convince us:

    diff t2.rb t3.rb

Limitations

• Very bad/little error handling

Ok, now what?

Once the first meta compiler is up and running we can evolve the language. For example I made a change so Ruby regexps can be used instead of only string literals. Note that we need to use a stepping stone syntax file before we can create a new meta compiler that accepts the new syntax.

Let's use this to compile programs which can only contain assignments of numbers to variables:

    .syntax assignments
    assignments = as *as;
    as = /\w+/ <'address ' $> ':=' ex1 <'store'> ';';
    ex1 = /\d+/ <'literal ' $>;
    .end

The new thing here compared to the original Meta-II syntax is the two Regexp's (in as and ex1). First we need to bootstrap the meta compiler that accepts regexps:

    rake bootstrap_re

Then we create a compiler for the assignments syntax:

    ruby bin/metacomp_re syntaxes/assignments.meta > tas.rb

We now have a compiler for assignments and if we apply it to the file:

    a := 137;
    b := 4;

by running the command:

    ruby tas.rb inputs/assignments.input1

it prints:

    address a
    literal 137
    store
    address d
    literal 4
    store

Not bad. :)