Transforming js_eval Results into Streams

[constraintAutomaton]

Hi,

I'm not sure if this is the right place to ask, but I was wondering if there is a way to transform the -Result of a js_eval statement into a stream.

Additionally, can something similar be done with foreign_struct?

[triska]

Maybe functionality to make a string available as a stream is needed?

[constraintAutomaton]

It seems like a good idea, but why not for every types that can be output by the ffi modules? But, I do not understand yet streaming in prolog.

[bakaq]

I've always wanted this, and it seems there is already internal code that does it that I've seen when I worked on streams last time.

[bakaq]

Why exactly do you want a stream there? And what do you mean by a stream? In Prolog a stream is a thing that you can possibly read and write, like a file handle in other languages. If you are talking more about an iterator-like thing, then Prolog doesn't have that in any official way but there are many ways you can do it.

[constraintAutomaton]

I am not sure because I am trying to implement incremental reasoning with a lot of data. I'll definitely look into prolog iterators. I need to prototype more.

[jjtolton]

What I want is a data structure that will not stock a whole "array" in memory, so that I can do some operation in the head of data structure and then discard the head and pull a new element to the head. So, it is more the memory management than I am looking for.

The bigger issue I'm seeing is that js_eval/2 will materialize the entire data structure, so unless you are materializing a lazy data structure, you won't get any memory savings from Prolog.

If you ARE using a lazy data structure, you could just "loop" and process until what you need is done.

loop(LazyData) :- 
   ( process(LazyData, LazyData1) -> loop(LazyData1)
   ; true
   ).

process(LazyData, LazyData1) :-
   first(LazyData, Head, LazyData1), % side-effecting on lazy data structure, maybe js interop? fails if empty
   do_something(Head). 

Now if you want loop to be "lazy", you will need to use library(cont), which is a whole thing.

If there are js promises involved, we are in some very different territory.

[constraintAutomaton]

Thank you! It helps. I also did not know the cont library.

[jjtolton]

Using library(cont) to implement cooperative concurrency is something I'm particularly interested in right now. If I manage to get anything working I will post about it somewhere here. It might be awhile though depending on work schedule :(

[constraintAutomaton]

I would like to know!