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https://issues.apache.org/jira/browse/LUCENE-6417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14639933#comment-14639933
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Jack Conradson edited comment on LUCENE-6417 at 7/24/15 5:06 AM:
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This patch contains the code necessary to upgrade to ANTLR 4.5.
The following changes are included:
* Updated the build.xml and ivy.xml to use ANTLR 4.5 instead of the prior
version.
* Modified the grammar to use only two parser rules including a left-hand
recursive rule for the majority of the language. Simplified the lexer rules.
* Used the provided visitor pattern classes ANTLR 4.5 provides to move through
the ANTLR parse tree. The JavascriptCompiler nows inherits from a
JavascriptBaseVisitor class. While this does add some extra methods, it's also
a well-known design pattern that can be easily modified by future contributors.
This allows for easy use of new rule context objects, so that some tokens may
be ignored that aren't necessary. Note that ANTLR 4.5 no longer has ASTs
because it does not allow for tree rewriting. The provided parse tree required
some changes to the compiler since the root nodes now contain 3 children with
something like '2' '-' '3' rather than tokens such as '-' with 2 children.
* Moved all error handling out of the grammar file making the grammar language
agnostic. Error handling is now part of separate java classes.
was (Author: jdconradson):
This patch contains the code necessary to upgrade to ANTLR 4.5.
The following changes are included:
* Updated the build.xml and ivy.xml to use ANTLR 4.5 instead of the prior
version.
* Modified the grammar to use only two parser rules including a left-hand
recursive rule for the majority of the language. Simplified the lexer rules.
* Used the provided visitor pattern classes ANTLR 4.5 provides to move through
the ANTLR parse tree. The JavascriptCompiler nows inherits from a
JavascriptBaseVisitor class. While this does add some extra methods, it's also
a well-known design pattern that can be easily modified by future contributors.
This allows for easy use of new rule context objects, so that some tokens may
be ignored that aren't necessary. Note that ANTLR 4.5 no longer has ASTs
because it does not allow for tree rewriting. The provided parse tree required
some changes to the compiler since the root nodes now contain 3 children with
something like '2' '*' '3' rather than tokens such as '*' or '-' with 2
children.
* Moved all error handling out of the grammar file making the grammar language
agnostic. Error handling is now part of separate java classes.
> Upgrade ANTLR to version 4.5
> ----------------------------
>
> Key: LUCENE-6417
> URL: https://issues.apache.org/jira/browse/LUCENE-6417
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Jack Conradson
> Attachments: LUCENE-6471.patch
>
>
> I would like to upgrade ANTLR from 3.5 to 4.5. This version adds several
> features that will improve the existing grammars. The main improvement would
> be the allowance of left-hand recursion in grammar rules which will reduce
> the number of rules significantly for expressions.
> This change will require some code refactoring to the existing expressions
> work.
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