Re: GLOBALSZ space problem...

[Lindsey Spratt]

I implemented XGP, an IDE for gprolog on the mac, that is implemented *in* 
gprolog. It runs fine. Menus, Windows, Graphics (drawing pictures); all done in 
gprolog as extended by XGP.

I make very slight use of globals - I would recommend parameter passing for 
state or asserting/retracting clauses where feasible. The parameter passing 
approach makes the best use of the prolog execution model with its semi-magical 
heap garbage collection.

I use the DCG notation a lot in various programs where I want to pass a context 
around among a collection of predicates.

Consider a predicate foo/3 that has a rule that passes a ‘modifiable’ context 
among three sub-goals, bar1/3, bar2/3, and bar3/3:

foo(s(X, Y, Z), InputContext, OutputContext) :-
  bar1(X, InputContext, InterimContext1),
  bar2(Y, InterimContext1, InterimContext2),
  bar3(Z, InterimContext2, OutputContext).

This can be written using DCG notation as:

foo(s(X,Y,Z)) —>
  bar1(X),
  bar2(Y),
  bar3(Z).

Then add a context modifying predicate such as 

context_p(c(P1,Q,R), c(P2,Q,R), P1, P2).

So bar1/3 can access the context using:

bar1(X, C1, C2) :-
  context_p(C1, C2, X, Y),
  Y is X + 1.

I’m a big fan of DCG programming in ‘stateful’ systems.

Lindsey

> On Aug 5, 2015, at 5:35 PM, emacstheviking <address@hidden> wrote:
> 
> I have written a lovely binding to SDL and I started developing an 
> application and it runs for a while then runs out of globals space.
> 
> In my wisdom, I decided to use globals to hold key items like app. 
> configuration and also the various SDL handles, window, renderer handles etc 
> instead of passing around more and more parameters.
> 
> If I can't solve this I am doomed! I will have to write my world class 
> application in something other than GNI Prolog.
> 
> Is gprolog "suitable" for a graphics based user application that might run 
> for a full working day and be subject to untold requests by users?
> 
> I've invested a *serious* amount of time in my gprolog/SDL2 project: it has 
> 87 SDL functions for lines, points, textures, window creation the lot, as 
> well as predicates for working with TTF fonts, music and samples, hey, I even 
> added some circle drawing in the c-code as well, solid and outline.
> 
> Why do I keep running out of space? I thought a "!" operation in my main loop 
> would do it, I discovered this when writing a proof oc concept video game 
> too, that seemed to be stable when printing out the statistics. I will have 
> to play spot the difference.
> 
> I tried commenting out stuff to pin it down but so far no luck, it just 
> slowly but surely leeks away until it dies.
> 
> I guess I just don't understand how garbage collection works.
> 
> Are g_assign and g_read designed to be hammered hard in a graphics 
> applications rendering loop?
> 
> Gutted!
> 
> Sigh, I hope somebody out there replies, this list seems dead in recent 
> months.
> 
> 
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