[antlr-interest] grammar for jdk1.5 parameterized types
Ernest Pasour
sasecp at wnt.sas.com
Fri Sep 19 06:09:19 PDT 2003
I looked at Jamie's solution, but I don't believe it works correctly (I may be wrong, I am no parsing expert). It appears that he has kept a counter that he increments when he sees LT and decrements on GT. Then he uses a syntactic predicate (I think that's what it's called) to prevent lexical recognition of ">>" if the counter is at 2. This forces the '>' to be recognized, which allows the parameterized types to be parsed. However, I believe a piece of code like the following will cause problems:
{
if (a<b) a++;
if (a<b) a++;
a>>2;
}
In this case, the ">>" will be recognized as two separate '>' symbols since it was preceded by 2 '<' without any intervening operation that zeroes out the counter.
-----Original Message-----
From: Terence Parr [mailto:parrt at antlr.org]
Sent: Thursday, September 18, 2003 3:02 PM
To: antlr-interest at yahoogroups.com
Subject: Re: [antlr-interest] grammar for jdk1.5 parameterized types
For some reason my last post didn't appear.
See the C++ templates added to Java solution by Jamie Herre on the
antlr site. Not sure what he did any more. However, it's a simple
matter in the lexer to track a tiny bit of context I think (i.e., did I
see "class" or a class name)? It means the lexer needs access to the
symbol table. I think Jamie did something clever, but can't remember.
Perhaps my audio lectures have the answer ;)
Ter
On Thursday, September 18, 2003, at 11:55 AM, John P N Pybus wrote:
> mzukowski at yci.com wrote:
>> You can't switch your lexer from the parser safely. ANTLR doesn't
>> work that way (infinite lookahead and all that). I suggest getting
>> rid of ">>" as a
>> token and making the parser look for '>' '>' as GT.
>>
>> Monty
>
> Hmm, with the lexer ignoring Whitespace wouldn't the parser then allow
> "n > > 3" as well as "n >> 3"?
>
> I'd suggest using lookahead in the lexer to define 3 tokens GT_GT,
> GT_EQ, and GT corresponding to a '>' directly followed by another '>';
> '>' followed by '=' and all other '>' chars, respectively.
>
> You can use ( GT | GT_GT ) in your parser rules for generics, and can
> define the various shift operators as GT_GT GT; GT_GT GT_EQ EQ etc...
>
> I haven't done this with the antlr java grammar myself, but I believe
> I've seen this approach used in other java1.5 recognisers (sorry no
> reference handy).
>
> Hope this makes some sense.
>
> Yours,
>
> John
>
>
>
>
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>
>
>
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