[antlr-interest] another milestone for v3.0
parrt at cs.usfca.edu
Thu Mar 17 13:02:19 PST 2005
Just this morning I was able to get ANTLR to *interpret* the java.g
grammar. In other words, instead of generating a parser in some
language, compiling it, and then running it on some java input, I was
able to parse Java w/o generating code or compiling at all. The result
of interpretation is a parse tree always. If there is a parse error,
it blasts out of the interpreter, but leaves an error node in the tree
indicating where the problem was.
The reason you care about this is because of the GUI dev environment.
Imagine prototyping a language. You're building the grammar and you
want to constantly check a small sample input against your grammar.
Generating code, compiling, and running it is a hassle. With the GUI,
you'll be able to immediately test input against the grammar or just a
single rule etc... :) Hooray!
BTW, the interpreter is actually pretty fast. :)
For the curious, here is what the code looks like that reads in the
java.g grammar dynamically and interprets an input file. Note that the
java.g file is a combined parser/lexer and hence the call to get the
lexer grammar from the original grammar. This seems pretty clean to me
for such a real world problem.
Grammar parser =
new Grammar("java.g", new BufferedReader(new FileReader("java.g")));
String lexerGrammarText = parser.getLexerGrammar();
Grammar lexer = new Grammar();
lexer.importTokenVocabulary(parser); // make sure token types line up
CharStream input = new ANTLRFileStream(args);
Interpreter lexEngine = new Interpreter(lexer, input);
CommonTokenStream tokens = new CommonTokenStream(lexEngine);
// parser tunes to channel one by default, ignores stuff on other
// can't execute actions in the lexer so I have to force certain tokens
// be ignored
System.out.println("tokens="+tokens.toString()); // print all tokens
Interpreter parseEngine = new Interpreter(parser, tokens);
ParseTree t = parseEngine.parse("compilationUnit"); // interpret
System.out.println(t); // print parse tree
CS Professor & Grad Director, University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
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