[antlr-interest] grammar for jdk1.5 parameterized types

[Anthony W Youngman]

I'm going to hit this problem ...

But can't you get the lexer to create eg

">>" will return tokens GT NWGT while
"> >" will return GT GT

So the parser, where it wants >, will accept either GT or NWGT, but if
you actually want >>, then it looks for GT NWGT or possibly NWGT NWGT

Cheers,
Wol

-----Original Message-----
From: mzukowski at yci.com [mailto:mzukowski at yci.com] 
Sent: 18 September 2003 19:57
To: antlr-interest at yahoogroups.com
Subject: RE: [antlr-interest] grammar for jdk1.5 parameterized types


Yep, you're right!

Monty

-----Original Message-----
From: John P N Pybus [mailto:john-yahoo at pybus.org] 
Sent: Thursday, September 18, 2003 11:56 AM
To: antlr-interest at yahoogroups.com
Subject: Re: [antlr-interest] grammar for jdk1.5 parameterized types


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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