Re: Push parsing from lexer?

[Mark Bannister]

Hi Alex
I see my mistake!  I read the docs incorrectly and presumed yypush_parse() was 
taking a function pointer.  Excellent, I think this is just what I want.
So in the example:
status = yypush_parse(ps, yylex(), NULL);
I take it that the first argument is yypstate* and the second argument is the 
next token. What is the third argument?  bison.info only appears to document a 
single-argument version (the impure version).
Thanks,Mark

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  On Wed, 14 Aug 2019 at 16:44, Martin Alexander Neumann<address@hidden> wrote: 
  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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