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Re: [Chicken-hackers] clarification of multiple evaluation of promises

From: John Cowan
Subject: Re: [Chicken-hackers] clarification of multiple evaluation of promises
Date: Mon, 13 May 2013 07:37:31 -0400
User-agent: Mutt/1.5.20 (2009-06-14)

Jörg F. Wittenberger scripsit:

> BTW: To those concerned with r7rs: I really don't like that the draft
> still leaves it undefined what the result of (force <promise>) is,
> if the promise returns multiple values.  force/delay are not that
> complicated to implement.  The way the r7rs draft is now, one would
> still need to duplicate the definition in applications if one wanted
> to be sure that multiple values are ok.

Because multiple values are not first class, supporting this requires
collecting the multiple values in a data structure such as a list,
remembering that they are not really a list but multiple values, and then
returning them as multiple values. You get no space benefit that way,
and might as well put a call to call-with-values inside the delay.

I have filed this as informal objection #532 at

Is not a patron, my Lord [Chesterfield],        John Cowan
one who looks with unconcern on a man 
struggling for life in the water, and when      address@hidden
he has reached ground encumbers him with help?
        --Samuel Johnson

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