me_intro - Man Page

Introduction to virtual machines for parsing token streams


This document is an introduction to and overview of the basic facilities for the parsing and/or matching of token streams. One possibility often used for the token domain are characters.

The packages themselves all provide variants of one virtual machine, called a match engine (short ME), which has all the facilities needed for the matching and parsing of a stream, and which are either controlled directly, or are customized with a match program. The virtual machine is basically a pushdown automaton, with additional elements for backtracking and/or handling of semantic data and construction of abstract syntax trees (AST).

Because of the high degree of similarity in the actual implementations of the aforementioned virtual machine and the data structures they receive and generate these common parts are specified in a separate document which will be referenced by the documentation for packages actually implementing it.

The relevant documents are:


Virtual machine specification.


Specification of various representations used for abstract syntax trees.


Utility commands.


Singleton ME virtual machine implementation tied to Tcl for control flow and stacks. Hardwired for pull operation. Uninteruptible during processing.


Object-based ME virtual machine implementation with explicit control flow, and stacks, using bytecodes. Suspend/Resumable. Push/pull operation.


Core functionality for state manipulation and stepping used in the bytecode based implementation of ME virtual machines.

Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category grammar_me of the Tcllib Trackers []. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.


CFG, CFL, LL(k), PEG, TPDL, context-free grammar, context-free languages, expression, grammar, matching, parsing, parsing expression grammar, push down automaton, recursive descent, top-down parsing languages, transducer, virtual machine


Grammars and finite automata


0.1 tcllib Grammar operations and usage