Re: Push parsing from lexer?

[Martin Alexander Neumann]

Hi Mark,

ah, yypush_parse does not take a pointer to yylex as second parameter,
the second parameter is the actual token (you have scanned somewhere else).

Yours,
Alex
On 14.08.19 17:28, Mark Bannister wrote:
> Hi Alex
> 
> Thanks for your reply, I had already read up on push parsers before my
> posting.
> 
> As you will see from the example on the Push-Decl page, yypush_parse()
> takes a pointer to yylex(), so the push parser will call my lexer in
> order to get tokens.
> 
> However, if in effect my lexer has the control loop, it already has the
> tokens so I would need a way of calling yypush_parse() with a token that
> I already have and not require it to make a separate call to yylex().
> 
> Is that possible?
> 
> Best regards
> Mark
> 
> Sent from Yahoo Mail on Android
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> 
>     On Wed, 14 Aug 2019 at 16:02, Martin Alexander Neumann
>     <address@hidden> wrote:
>     Hi Mark,
> 
>     please have a look at instructing Bison to generate a push parser
>     instead of a pull parser (which is the default):
> 
>     https://www.gnu.org/software/bison/manual/html_node/Push-Decl.html
> 
>     Yours,
>     Alex
> 
>     On 14.08.19 09:14, Mark Bannister via help-bison wrote:
>     > I am writing a Bison re-entrant push parser with my own lexical
>     analyser.  However, if my understanding is correct, the only way I
>     know to make this work is a bit inefficient.
>     > I have a debugger interface that I'm developing that takes one
>     line of input at a time.  The debugger then decides which language
>     module to call based on a simple pattern match.  It invokes an
>     entry-point in the correct module with the line of input it has
>     received.  Only one of the language modules will use bison, the
>     other interfaces are too simple to need it.  Once I am in the
>     language module I am scanning for tokens and some simple context. 
>     For example, it's possible to call out to another language module
>     from here too so this loop cannot be implemented in bison as the
>     full grammar cannot be defined at this point. Also, the syntax
>     structure may be varied depending on the value of a variable, and
>     this affects whether or not a complete statement is or is not
>     terminated by semicolons, for example.
>     > What I would like to do is call my bison parser for each token
>     that I collect in the main loop of my language module, and from
>     there I can create an AST.  So, for example, I would go:
>     > Debugger -> Module Loop -> Bison (per token) -> AST
>     > This obviously requires a push parser, but the problem I am facing
>     - and the reason for my call for help - is that bison wants to call
>     a lexer even though I already have the token I need to push to it. 
>     So it appears to be back-to-front.  The only way I can think of
>     right now to solve the problem is to store my token in a structure
>     that I pass by reference to bison, which it passes to a lexer
>     function that just extracts the details and returns it back to
>     bison.  I think this should work but it is suboptimal and looks like
>     this:
>     > Debugger -> Module Loop -> Bison (per token) -> lexer (return
>     token) -> Bison -> AST
>     > Is there a better way?
>     > Best regardsMark
>     >
>     > Sent from Yahoo Mail on Android
> 
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