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Re: [Scheme-reports] Some comments after reading the r7rs public draft

On Thu, 2012-06-07 at 15:30 -0400, John Cowan wrote:

> Please let me know if you object to the presence of either note.

At the moment, I am inclined to object to both. The idea behind DELAY
and FORCE is that at some point you are intentionally saying, "Do not
evaluate this yet," and at some later point, "Now you should evaluate
this."  I think the terms DELAY and FORCE strongly suggest this
interpretation, and as you pointed out, the semantics of all major
implementations coincides with this. Additionally, creating a large
unspecified set of valid uses of force (involving parameters) just to
enable an optimization that is likely to be undesirable in many cases,
and for which a perfectly valid and more obvious solution exists,
reduces the value of DELAY and FORCE to an extent that I find

I do not think we should use space to mention this issue, but
implementations are obviously free to use threads to evaluate suitable
delayed expressions if they follow the correct behavior, as Alex

Thus, instead, I would prefer to clarify that a forced thunk should
evaluate in a context equivalent to the dynamic context (including
exception handlers and parameters) of the call to force which first
requested the delayed expression's value.

Aaron W. Hsu | arcfide@x | http://www.sacrideo.us
Programming is just another word for the lost art of thinking.

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