Re: Push parsing from lexer?

[Mark Bannister]

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 regardsMark

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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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