Re: Benchmarks of guile-www against HB's Guile module.

[Neil Jerram]

>>>>> "Alejandro" == Alejandro Forero Cuervo <address@hidden> writes:

    Alejandro> Hey. :)

    Alejandro> Thanks for your cooperation, Neil.

I'm getting there, slowly :-)  (And I also appreciate that thi has
given you useful answers to your questions in another thread.)

    Alejandro> You suggest the following: [...]

    Alejandro> I can't see a difference with doing the following:

    Alejandro>     SCM hb_register (SCM name, SCM proc)
    Alejandro>     {
    Alejandro>       HB_FILE *hb_file = hb_get_current_file();

    Alejandro>       hb_file = hb_get_current_file();

    Alejandro>       ...;
    Alejandro>     }
    
    Alejandro>     init_hb ()
    Alejandro>     {
    Alejandro>       gh_new_procedure2_0 ("hb-register", hb_register);
    Alejandro>     }

I agree, there's no difference.

    Alejandro> Does your answer mean I'm forced  to declare a global variable 
(where is
    Alejandro> hb_get_current_file going  to get the current  file from?) if I  
want to
    Alejandro> have  it passed  to my  function?  Is  there no  way to  
register a  new
    Alejandro> procedure associating it a void pointer?

OK, I think I finally get it.  There is only one "current file" at any
moment, but it changes from time to time.  And, whenever it changes,
you want to redefine `hb-register' by calling, ideally,
gh_new_procedure2_0_data.  And you'd prefer not to keep a global
variable around in C to remember what the current file is.

If I'm now understanding correctly, you can achieve this using the
general idea of closure, but you have to involve the Scheme level, as
C primitives don't support closure.  [Aside: so what is a "C closure"
then?  I may be missing something here.]  And it is more tricky than
the example I referred to in the manual.

Suppose the C function that does all the work is

SCM hb_register_internal (SCM file, SCM name, SCM proc)

and is exported to the Scheme level as `hb-register-internal'.

Now take this Scheme code:

(set! hb-register #f)

(define (setup-hb-register file)
  (set! hb-register
        (lambda (name proc)
          (hb-register-internal file name proc))))

Whenever you call `setup-hb-register', it rebinds `hb-register' to a
new procedure which takes two args - NAME and PROC - and which has the
right FILE stored in its environment.  So users calling `hb-register'
don't need to mention the FILE argument, but `hb-register-internal'
will always receive the FILE that was originally passed to
`setup-hb-register'.  Cunning, huh?

That just leaves you with two problems:

1. You need to wrap HB's file structure somehow as a SCM value.  But I
believe you've already done this.

2. You need to call `setup-hb-register' from C.  I believe the proper
   way to do this is:

scm_call_1 (SCM_VARIABLE_REF (scm_c_lookup ("setup-hb-register")),
            file);

where file is the current file structure wrapped as a SCM value.

Am I any closer this time?

        Neil