Re: Pure (side-effect-free) calls into c/c++?

[Linus Björnstam]

I have a macro called lambda/memo and define/memo for these situations: 
https://hg.sr.ht/~bjoli/misc/browse/default/memoize.scm

If the function gets called with a gazillion different arguments the 
memoizatiin hash gets large, and there are no mechanisms to stop that from 
happening. It also lacks a fast path for single argument functions.

You can disregard the repo license. Use that function is you like, if you like 
to.


-- 
  Linus Björnstam

On Fri, 10 Jan 2020, at 23:36, Linas Vepstas wrote:
> So, I've got lots of C code wrapped up in guile, and I'd like to declare
> many of these functions to be pure functions, side-effect-free, thus
> hopefully garnering some optimizations.  Is this possible? How would I do
> it? A cursory google-search reveals no clues.
> 
> To recap, I've got functions f and g that call into c++, but are pure (i.e.
> always return the same value for the same arguments).   I've got
> user-written code that looks like this:
> 
> (define (foo x)
>     (g  (f 42) (f x) (f 43))
> 
> and from what I can tell, `f` is getting called three times whenever the
> user calls `foo`. I could tell the user to re-write their code to cache,
> manually: viz:
> 
> (define c42 (f 42))
> (define c43 (f 43))
> (define (foo x) (g c42 (f x) c43))
> 
> but asking the users to do this is .. cumbersome.  And barely worth it: `f`
> takes under maybe 10 microseconds to run; so most simple-minded caching
> stunts don't pay off. But since `foo` is called millions/billions of times,
> I'm motivated to find something spiffy.
> 
> Ideas? suggestions?
> 
> -- Linas
> -- 
> cassette tapes - analog TV - film cameras - you
>