Hi Ben,
I can't help you with the Python part, but below is a quick & dirty
grammar for Java which more or less does do what you want.
Most likely your errors will come from the lexer, hence I throw the
exception there to show you. So in your python program catching that
should tell you it was wrong. The rest of the grammar fills a list
with text or numbers that are parsed, and prints it in the @after of
begin rule (which is only there so a quick printout was possible).
Martijn
grammar test001;
@lexer::members {
@Override
public void reportError(RecognitionException e) {
throw new RuntimeException(e);
}
}
@members {
java.util.List result = new java.util.ArrayList();
public List getResult() {
return result;
}
}
begin
@after {
System.out.println("RESULT=" + result);
}
: expr
;
expr
: what (DOT expr)?
;
what
: TEXT
{
if($TEXT.text != null) {
result.add($TEXT.text);
}
}
| NUMBER
{
if($NUMBER.text != null) {
result.add($NUMBER.text);
}
}
;
DOT
: '.'
;
TEXT
: 'A'..'Z'+
;
NUMBER
: '0'..'9'+
;
WS : ( ' '
| '\t'
| '\r'
| '\n'
) {$channel=HIDDEN;}
;
On Mon, Sep 7, 2009 at 5:18 PM, Ben<[email protected]> wrote:
> Hi all, I'm trying to use the Python backend. I wanted to start with
> something simple and I didn't see an example like this either in Parr's book
> or on the wiki.
>
> So, suppose I just want to recognize a string with (uppercase) letters and
> numbers separated by a dot. The parse function needs to return the letters
> and numbers separately, or else the value None if the expression doesn't
> parse. Below are how it might be done with regular expressions, and how I've
> tried to do it with ANTLR3 using the AST generator.
>
> ============== Regular expression example
> import re
>
> def parse(s):
> """Parse string s and return pair [letters, numbers]"""
> m = re.match("([A-Z]+)\\.([0-9]+)$", s)
> return (m.group(1), m.group(2)) if m else None
>
> ============== My ANTLR attempt: Example.g
> grammar Example;
>
> options {
> language=Python;
> output=AST;
> ASTLabelType=CommonTree;
> }
>
> @lexer::members {
> def reportError(self, e):
> raise e
> }
> @members {
> def mismatch(self, input, ttype, follow):
> raise MismatchedTokenException(ttype, input)
>
> def recoverFromMismatchedSet(self, input, e, follow):
> raise e
> }
> @rulecatch {
> except RecognitionException, e:
> raise
> }
>
> expr : LETTERS '.' NUMBERS EOF -> LETTERS NUMBERS;
>
> LETTERS : 'A'..'Z'+ ;
>
> NUMBERS : '0'..'9'+;
>
> ============== My ANTLR attempt: example.py
>
> import StringIO
> import antlr3
> import ExampleLexer, ExampleParser
>
> def parse(s):
> """Parse string s and return pair [letters, numbers]"""
> stringio = StringIO.StringIO(s)
> char_stream = antlr3.ANTLRInputStream(stringio)
> lexer = ExampleLexer.ExampleLexer(char_stream)
> tokens = antlr3.CommonTokenStream(lexer)
> parser = ExampleParser.ExampleParser(tokens)
> try: expr = parser.expr()
> except antlr3.RecognitionException: return None
> return tuple(child.text for child in expr.tree.getChildren())
>
> ============== End code
>
> So first, do I have the right basic idea here? It seems to be getting pretty
> complicated and already into some undocumented stuff for a simple example.
>
> Second, this example still doesn't really work, because it still matches
> strings like "3452EOUSNTHO.32423AOE" that it shouldn't. Also, this solution
> is hard to package because the modules in the antlr3 runtime refer to other
> antlr3 modules like "antlr3.streams" instead of just "streams" so I have to
> start messing with python's module path. How can I fix this?
>
> Thanks for any advise,
> --
> Ben
>
>
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