[plt-scheme] Project Euler was Hash Table implementation

The revised implementation of SRFI-40 uses the delay and force of SRFI-45.

On 8/4/07, Will M Farr <farr at mit.edu> wrote:
>
> On Aug 4, 2007, at 5:33 PM, David Einstein wrote:
>
> > I was the one who said that srfi-40 streams are tricky.  The fact that
> > they do not always delay when you expect them to coupled with the fact
> > that mzscheme 370 will occasionally crash on windows when you run out
> > of memory (even with memory limited) has caused me a certain amount of
> > anguish.  It took me a while to get an intuitive sense of what was
> > going on, but now it pretty much makes sense.  I suspect that either
> > too many forces, or too few delays are the penalty one pays for lazy
> > programming in an eager language (the Wadler paper is on my to read
> > list.)
>
> As an aside, you might have a look at SRFI-45 (http://
> srfi.schemers.org/srfi-45/srfi-45.html ); it introduces a new
> primitive, (lazy ...), which acts like an atomic (delay (force ...))
> from SRFI-40, but does so "tail-recursively".  This means that many
> lazy algorithms which should be iterative, but are not with the
> (delay (force ...)) of SRFI-40, truly become iterative.  (See the
> srfi document for an extensive discussion of the problems with (delay
> (force ...)) and unbounded allocation with algorithms that should be
> iterative.)  Perhaps some of your problems running out of memory
> could be avoided this way?
>
> Will
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