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Author image Jeffrey Kegler
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Marpa::Doc::To_Do - Marpa's To Do List


  • Allow cloning of unstripped recognizers

  • Add a SYNOPSIS to the Plumbing document.

  • Parse bocage creation can probably be made a bit slightly cleaner. At least I think so, based on what I found when revising that part of the Internals doc.

  • Make sure that nulling symbols can never be terminals


  • Better evaluation of sequences -- just push onto an array via a ref, reversing at the end if necessary. All that code could use better comments.

  • Add a trace_choices option. There was an option to trace non-trivial evaluation choices in the old evaluator, and the new trace_iterations doesn't entirely replace it.

  • Add a show_derivation option.

  • Add to test set: Basic tests of sequences. The matrix is separation (none/perl5/proper) and minimium count (0 or 1). Eliminate keep vs. no-keep, right vs. left.


  • Test lexing suffixes? Remove them?

  • Speed-up for pre-computing lexables? Predict lexables based on user request?

  • show_tree before first call to value? Should it cause an error message? How about after unsuccessful call to value?


For the moment, I will do only bug fixes on the Marpa Demonstration Language, or features for which there is specific demand from the users. I'm currently thinking of creating another interface language, with syntax like Perl 6 regexes and the PGE input. So for the time being, nothing will happen on any of the items in this section.

Terminal Priorities Cannot Be Set in MDL

Priorities cannot be set in MDL for terminals. So far there's been no need for this, and I don't want to invent an artificial test case. Once there is an application, I will use that as the test case.

Workaround: Add extra rules with the terminals you want to prioritize on their right hand side, and assign priorities to the rules.

Other MDL Changes

  • Allow alternation?

  • Downgrade version conflict or semantics mismatch to warning?

  • Add {} and [] syntax to MDL production statements.


Lifting Restrictions on Sequence Productions

The restriction of sequences to sequence productions and of sequence productions to a single sequence is not the result of any limit of the Marpa parse engine. It would not be hard to allow any number of sequences and optional sequences on the right hand side of any BNF production. I'm open to revisiting this issue and lifting the restriction.

The problem is figuring out how to conveniently specify their semantics. As the right hand side of a production grows more complex, the semantics becomes more complex to write, more bug-prone, and harder to debug.


See the support section in the main module.


Jeffrey Kegler


Copyright 2007 - 2009 Jeffrey Kegler

This program is free software; you can redistribute it and/or modify it under the same terms as Perl 5.10.0.