Some tools output an Antlr grammar in a human-unreadable form, at least with ugly placing of parens and indentation. I'd like to transform the grammar into a more readable (standard?) form. The only reference I found is ANTLR pretty printer which is quite old, and looking at its source, it seems to be removing parts of a grammar rather than pretty print it.
How can I format/pretty print a grammar file?
I know of no tool that does this. The one you mentioned, prettyPrinter, is written in - and seems to handle only - ANTLR v2.x grammars, making it unsuitable for v3 grammars.
If you're going to write your own, I'd recommend using the grammar of ANTLR v3 itself to parse a .g grammar file and emit it in a readable form. Terence Parr has posted the grammar here: http://www.antlr.org/grammar/ANTLR
I just installed an Antlr plugin for Eclipse. It can do a lot more than syntax highlight and code formatting...
Related
I am wondering if I can generate ANTLR grammar from java source code. I want to do some kind of research project, but I am just exploring different open sources to see which one is best.
For ANTLR, do I always have to write a grammar and pass it to the ANTLR?
Is there a way to generate grammar from an existing Java source code?
Not easily. ANTLR generate a recursive descent parser from your grammar, encoding the tests into procedural code, as well as lots of other bookkeeping stuff.
Knowing how the code is generated, you might be able to take it apart but you'll have to reach into the middle of generated statements and that isn't easy without a full parser for the generated language. (Hint: regex won't work).
I don't see a lot of point of this exercise. Why don't you just use the original grammar?
I'm new to Xtext and wondering what's the purpose of antlr is in xtext. As I've understand so far, antlr generate a parser based on the grammar and the parser then deal with the text models. Right?
And what about the other generated stuff like the editor or the ecore. Are there other components behind xtext which generate them?
Xtext needs a parser generator to produce a parser for the language you define. They could have built one of their own. They chose to use ANTLR instead.
I don't know what other third party machinery they might have chosen to use.
I've been hacking one Xtext based plugin and from what I saw I think it works like this:
Xtext has it's own BNF syntax, which is very similar to ANTLR one. In fact its it's subset.
Xtext takes your grammar, and generates the ANTLR one from it(.g file). The generated ANTLR grammar adds specific actions to your BNF rules. The actions code interacts with the Xtext runtime and (maybe) with the Eclipse itself. The .g file is processed using some older version of ANTLR and .java file is generated. This file is then compiled.
Anybody know of a tool, that generates EBNF from ANTLR?
ANTLR is already close to EBNF, but for documentation purpose I would like to have a clean EBNF description (without the Code in between).
With antlrworks and this its already nice to get the syntax diagrams:
java -cp antlrworks-1.1.4.jar org.antlr.works.Console -f yql.g -o output/ -sd eps
but it would like to have a bare textual description, preferable text, tex, html, xml, or similar.
I have an online tool that converts foreign grammars to W3C grammar notation. It has an ANTLR3 grammar parser, so maybe this gets close to what you were looking for. W3C notation is also useful for generating syntax diagrams.
I have a little bit large ANTLR parser grammar file and want to make a tree grammar for it. But, as far as I know this work of tree grammar generation can't be done automatically, i.e., I should generate it manually by copying parser grammar, removing some unnecessary code, etc. I want to know if there is a systematic way to generate a tree grammar file from a parser grammar file.
P.S. I read an article that insists that 'Manual Tree Walking Is Better Than Tree Grammars'. Is this reliable information? If so, would it be better for me to make a manual tree walker than writing an ANTLR tree grammar file? And then, how do I make a manual tree walker with my ANTLR parser grammar file(it makes an AST using rewrite rules)?
Thanks in advance.
sky wrote:
I want to know if there is a systematic way to generate a tree grammar file from a parser grammar file
You've already described the systematic way to do this: copy the parser/production rules in the tree grammar and only leave the rewrite rules in it. This will probably handle the larger part of your rules, but with other parser rules (using inline AST rewrite rules), it might look slightly different. Because of that, there is no automatic way to generate a tree grammar.
sky wrote:
P.S. I read an article that insists that 'Manual Tree Walking Is Better Than Tree Grammars'. Is this reliable information?
Yes, it is. Note that Terence Parr (creator of ANTLR) posted the article on the ANTLR wiki himself, so that says the author of it (Andy Tripp) raises valid points.
sky wrote:
If so, would it be better for me to make a manual tree walker than writing an ANTLR tree grammar file?
As Andy mentioned in his conclusion: "The decision about whether to use a "Tree Grammar" approach to translation vs. just "doing it by hand" is a matter of taste.". So, if you think writing tree grammar is too much hassle, go the manual way. It's up to you: there is no best way here.
sky wrote:
And then, how do I make a manual tree walker with my ANTLR parser grammar file(it makes an AST using rewrite rules)?
Your parser will create an AST, which by default is of type CommonTree (API-doc). You can use that tree to get the children, the parent, the type of the token etc.: all you need to manually walk the tree.
EDIT
Note that in the next version of ANTLR (version 4) it will (most likely) be possible to automatically generate a tree walker given a combined- or parser grammar.
See:
https://web.archive.org/web/20130620232750/http://www.antlr.org/wiki/display/~admin/ANTLR+v4+plans
https://web.archive.org/web/20130927174157/http://www.antlr.org/wiki/display/~admin/2011/09/05/Auto+tree+construction+and+visitors
https://web.archive.org/web/20130927175520/http://www.antlr.org/wiki/display/~admin/2011/09/08/Sample+v4+generated+visitor
As an project assignment, I need to parse a plain-C grammar from Java to generate AST output. As a startup, I am using the file c.jj that I have found among grammar files at
http://java.net/projects/javacc/sources/svn/
but I found that it only has syntactic and lexical actions and no real semantics for parsing C source. Is there some other source that incorporate typedef, variables, construct functions, include files?
You could go looking for a complete grammar. Will you learn much this way?
You could ask your lecturer which would impress them more: implementing some small subset of C grammar by writing your own rules, or by searching google for alternative complete rules?
I trust writing your own rules - and even your own hand-crafted parser - will be more a more useful exercise. Even if its only parsing expressions.