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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
<http://trac.sacrideo.us/wg/ticket/532>.
--
Is not a patron, my Lord [Chesterfield], John Cowan
one who looks with unconcern on a man http://www.ccil.org/~cowan
struggling for life in the water, and when address@hidden
he has reached ground encumbers him with help?
--Samuel Johnson