Re: [ANN] New library stream.el in ELPA

[John Wiegley]

>>>>> Nicolas Petton <address@hidden> writes:

> Here is an example implementation of the Fibonacci numbers implemented as in
> infinite stream:

>     (defun fib (a b)
>       (stream-cons a (fib b (+ a b))))
>     (fib 0 1)

How bizarre, just yesterday I started a file called "thunks.el" to generalize
this kind of behavior. Since I didn't get very far, I'm glad to see the idea
taking shape elsewhere!

What I wonder is, can you generalize this beyond cons cells?  I mean, can we
have a general lazy evaluation framework, instead of just lazy lists?  The API
I was thinking of was:

    (let ((x (thunk-create FORM)))
      (thunk-eval x))

The idea being that 'x' is a self-modifying thunk which only evaluates FORM
the first time it is forced, but immediately returns the result value after.

I think that stream-cons and seq-take could be implemented on top of this
lower-level behavior.

John