Specification

This document strictly outlines the defined behaviour for the META Compiler writing language.

Matching

META matches a set of characters when written as a string.

These matches will not be pushed onto the stack

RULE = "some string";
// Will only match "some string"

Variables

Variables in META are prefixed by a & (and) sign to differentiate them from parse rules, valid characters are:

[A-Za-z_][A-Za-z0-9_]*

[define variablename "awd"]

RULE = &variablename;
// Will match "awd"

The Stack

Every match except for raw strings will be pushed onto a global stack that can be accessed by either using .STACK or it’s shortcut %. Indexing the stack is done in reverse, meaning that 0 will resolve to the last element on the stack, 1 to the second to last one and so on. If you want to index the stack from the start, you may use negative offsets.

RULE = .NUMBER %[0];
// Will match any number that occurs twice, like "4 4"

Slicing the stack

The stack is an array of strings, or a **char[]. It can be sliced using comma indexing.

• %[...,] Reverse indexing, will slice it from the end to the front of the array.
• %[,...] Forward indexing, will slice the array from the front to the specified offset in ....

RULE = $.NUMBER %[0,];
// Will parse everything in reverse, like "1 2 3 3 2 1" will resolve but "1 2 2" won't.

Capture

Capturing is quite important in some cases when using META. Every match will be pushed onto a stack where it can be collected later on.

RULE = .NUMBER ~ #
// &num doesn't exist in the current scope so it will be created and the last element on the stack will be assigned to it.

Scopes

Additional scopes may be created when certain output or input buffers need to be used.

RULE = @(ID) ~ &scope;