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1 point by almkglor 5774 days ago | link | parent

> Does it mean positive interesting, as in you'd be interested in trying it?

This one. If it were the negative interesting, I'd ask you directly "what for?" ^^

Hmm. Although it might be difficult to do with a copying GC.

As an aside, I'm thinking of exposing the "sharedvar" objects into arc, basically they would be called the "container" type. An arc-on-mzscheme implementation would be:

  (require "lib/settable-fn.arc")
  (def container ((o val))
    (add-attachments
      '= (fn (v) (= val v))
      (annotate 'container
        (fn () val))))
Basically it would be used this way:

  (= foo (container 0))
  (foo)
  => 0
  (= (foo) 42)
  (foo)
  42
Basically assigning to it would be equivalent to setting the pointer, and (foo) would be equivalent to (* foo) in C.

I thought it might be useful in a C FFI (when I get there in, say, T=inf). If a C function accepts a int*, for example, where it would put an int, you would pass in a container, which would automagically get the int.



1 point by shader 5774 days ago | link

Sounds like a reasonable syntax. Would the value in a container in a container be accessed with ((foo))? It fits, but it might get old after a while.

Also, how similar would these "containers" be to pointers? It doesn't seem like it would be as useful, because I doubt you can increment/decrement a container.

So, what are the problems we might encounter if we actually use this?

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1 point by almkglor 5774 days ago | link

The value pointed to by the container would be accessed with (foo), just a single layer of parens. The container's pointer would be mutated as (= (foo) ...) though. Oh well.

Edit: Oh, you said "container in a container". Yes, ((foo)) it is.

> It doesn't seem like it would be as useful, because I doubt you can increment/decrement a container

This functionality would be in a scanner, although a scanner, technically, would be just an iterator.

For instance, I fully intend to implement string scanners and input file scanners on the C++-side in SNAP; they would be somewhat "safe" wrappers around C++ iterators, which are just a generalization on the pointer. so (car foo) would be *foo and (cdr foo) would be (foo + 1).

> what are the problems we might encounter if we actually use this?

None at all, if you're talking about just containers and scanners. A container is just a reference to an Arc object. A scanner would just be an Arc-safe wrapper around an iterator.

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1 point by almkglor 5724 days ago | link

http://okmij.org/ftp/Scheme/pointer-as-closure.txt

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