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Re: Strange behavior with delayed objects

From: Andy Wingo
Subject: Re: Strange behavior with delayed objects
Date: Fri, 21 May 2010 12:59:31 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)


On Fri 14 May 2010 23:53, user8472 <address@hidden> writes:

> The solution is thus to wrap the defines in (lambda () ...)s.
> <code>
> (define (solve f y0 dt)
>   (define (y) (integral (delay (dy)) y0 dt))
>   (define (dy) (stream-map f (y)))
>   (y))
> (debug-set! stack 2000000)
> (stream-ref (solve (lambda (x) x) 1 0.001) 1000)
> </code>
> will produce the correct answer. The downside is that the function calls
> will be wrapped recursively which necessitates increasing the stack size.
> Plus, it's much slower this way. But it works.

The fact that it's slow is an implementation detail. Lambda expressions
are simply abstractions over scope -- they do not necessitate the
creation of closures. Guile 2.0 is already much faster for this case,
I believe, and with a proper inliner, y and dy would not actually be
implemented with functions.


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