Re: Creating inline closures

[Ilya Zakharevich <nospam-abuse@ilyaz.org>]

On Sat, Dec 08, 2018 at 02:15:17PM +0100, Bill Allombert wrote:
> >       Suppose I have a C function
> >         GEN mysummand(GEN I, void *mydata);
> >       It is completely unclear how can I make out of it something to
> >       pass to (e.g.) somme() to make an analogue of
> >         sum(I=1,3,mysummand(I))
> 
> Hello Ilya,
> 
> To help you to upgrade, I join a program that should do what you want.
> 
> 1) use pari_add_module to add your functions to GP.
>   pari_add_module(functions_ilya);

???  Why would I want to expose my function to the interpreter, if it
     is not usable standalone?

> 2) use strtoclosure to create the partial function as t_CLOSURE object
>   fun = strtoclosure("_ilya_mysummand",1,stoi((long)&mydata));
> This returns a t_CLOSURE x -> mysummand(x, &mydata)

It looks like a very strong overkill.  As far as I can see, (1)+(2)
can be replaced by a call to snm_closure().

> At this point you can use the t_CLOSURE directly in functions like
> apply that need a true closure (code "G" or "J")

I do not care about these anyway…

> 3) for functions like sum that need a inline closure (code "E" or "I"),
> you need to create a gadget that will inline your closure inside the
> sum. The simplest is to use the GP compiler:
>   sum_gadget = gp_read_str("(a,b,C)->sum(i=a,b,C(i))")
> and then use closure_callgenall to evaluate it with C set to your
> closure.
>   s = closure_callgenall(sum_gadget, 3, stoi(1), stoi(3), fun);

Using a compiler is exactly what I want to avoid.

It looks like what I need is essentially a new function
snm_lex_closure() with exactly the same semantic as snm_closure(), but
taking the first n C-arguments not from GP-arguments, but from the
last n defined lexical variables.  (So the produced function is 0-ary,
same as an inline closure.)

But thanks anyway,
Ilya

P.S.  What does snm_ mean?