Grammatica TODO-List

Known Issues

This is a list of the known issues as of the release of version 1.6 (2015-05-17). Please verify that any new problem found is not in this list before sending a bug report.

• Parser: Some grammar ambiguities may go undetected
  When the last element of an alternative is optional, some ambiguities may go undetected. This is due to not properly comparing the tokens in the optional element with the tokens after the production. The ambiguious grammar A = B ["x"]; B = "y" ["x"]; illustrates this. In some cases this may also lead to parse errors as ambiguities have not been resolved with the appropriate number of look-ahead tokens. This error is present in all versions of Grammatica, but occurs infrequently. Bug #4117

Suggested Improvements

This is a list of the currently known suggested improvements.

• Grammar: Add support for modular grammars
  By allowing one grammar to reference another, it would be possible to create more complex modular parsers. This feature also requires support for modular tokenizers and parses, as well as the generation of modular code. Bug #3599
• Grammar: Add localization support
  This includes finding an architecture that works for grammar files, making it possible to localize the error messages without rewriting the grammar file. This architecture must support different methods depending on generated source (ResourceBundles in Java, Gnu Gettext in C & C++). Bug #3600
• Grammar: Production representation should be improved
  The internal representation of a production makes it hard for several alternatives to share a several left-hand side elements. This may cause inherent ambiguities to be found, as the number of look-ahead tokens needed to separate the alternatives is infinite. If these alternatives could share the first elements, this ambiguity would not require a rewrite of the grammar. Bug #4322
• Grammar: Identical productions should be unified
  Identical syntetic productions are not indentified as such. Instead, a new syntetic production is added in each case. This will cause problems for LR parsers, and is generally inefficient. Identical syntetic productions should be unified. Bug #3602
• Tokenizer: Add support for modes
  When reading certain tokens the tokenizer should be able to enter some kind of "mode", limiting the set of tokens that are considered for a match. This is highly useful in some grammars, where the token syntax isn't easily represented with regular expressions. Bug #3604
• Parser: Add support for LR grammars
  This probably means writing at least an LALR(1) parser, and probably also some kind of LR(k) parser. Bug #3606
• Parser: Add parsing through code callbacks
  This would allow more complex grammars to be parsed where some productions cannot be expressed in EBNF. Instead a callback method would be called to parse some specific productions. Bug #3607
• Analyzer: Allow node values propagating downwards
  Improve the analyzer framework to handle node values propagating downwards or sideways in the tree as well. Bug #3608
• Code Generation: Support creation of a C parser
  This requires the writing of a C runtime library. Bug #3609
• Code Generation: Support creation of a C++ parser
  This requires the writing of a C++ runtime library plus appropriate code generation classes. Bug #3610
• Error Handling: Add file reference in errors
  The exceptions could be extended with a file location object (a file reference) to simplify the error handling when several files are parsed. Bug #4180

Grammatica 1.6 (2015-05-17). See the Grammatica web site for more information.

Copyright © 2003-2015 Per Cederberg. This document is distributed as part of Grammatica under the BSD license.