Re: Parsing from continuous stream

[Bob Rossi]

On Sat, Jan 19, 2008 at 05:33:32PM +0000, Daniel Kraft wrote:
> Hi,
>
> I'm trying to use GNU bison to parse from a "continuous" stream, that is, I 
> do want to implement a program similar to a shell:  parse one "command" at 
> a time, process it, and continue until end-of-stream is encountered.
>
> However, I do want my parser to return the parsed tree to the calling 
> program to process it on each step, so ideally I'd like bison to return 
> from yyparse() when a complete instance of the start symbol is read, but it 
> seems it does not do this (waits for special 0-token, as far as I found 
> out)--to counter-act, I currently do something like this:
>
> start_symbol:
>   real_start_symbol
>   {
>     storeValueForProcession($1);
>     YYACCEPT;
>   }
> ;
>
> This works, except that the YYACCEPT seems to discard the current 
> look-ahead-token if some has been read, meaning it is missing from the 
> input when parsing the next step.
>
> I'm aware that I could do the processing right inside the bison action 
> instread of returning the token value, but this is something I'd like to 
> avoid because it does not fit in well with my current design.  Is there 
> some way I can make bison return whenever the start-symbol is successfully 
> reduced and keep its stack and the like so I can continue parsing the next 
> instance of it with the next call to yyparse()?

Aha, Yes!

Use the push parser that I have just implemented in Bison. You will be
the first beta tester. The documentation should be in CVS and you need a
CVS version of bison.

Bob Rossi