On Thu, Sep 4, 2014 at 9:42 AM, Alex Shinn <alexshinn@gmail.com> wrote:
>
> The original question was whether cycles were possible in "strict
> immutable structures."  I would allow promises as part of that
> structure, and consider them immutable so long as they aren't using
> mutable variables or data structures.

OK, so IOW nothing new.

> There's no reason immutable pairs couldn't be implemented in terms of
> promises, in which case the tying the knot trick could be used (under
> the hood) to provide utilities for generating cyclic immutable lists.

IME, it comes out like regular code -- not much different from Racket's
reader graphs which are used to implement cyclic cons structures.  (Only
that requires an explicit step that turns the "reader graph" into a
sexpr.)

--
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!

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