Newsgroups: comp.lang.scheme
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From: hbaker@netcom.com (Henry Baker)
Subject: (Force-able) Delays First-Class in Scheme???
Message-ID: <hbaker-1710951136260001@10.0.2.15>
Sender: hbaker@netcom19.netcom.com
Organization: nil organization
Date: Tue, 17 Oct 1995 19:36:26 GMT
Lines: 25

I know that Scheme provides for expressions of the form (delay <exp>),
which can be forced (touched) using (force <delayed object>).  The question
is whether Scheme requires these objects to be truly first-class lazy
objects -- i.e., whether (+ (delay 3) (delay 4)) and
(if (delay (< 4 3)) (foo) (bar)) will always work.

My R^4 report (Lisp Pointers IV,3 (1991)) says that delays aren't
guaranteed to be first-class.  Has this been changed/upgraded??

----

Whether or not this is required, which Schemes currently implement
first-class delays??

I understand from Miller's PhD thesis that MultiScheme implemented first
class delays.  Are there any others?

----

Has 'delay'/'force' been a big hit in the Scheme community?  Or are they
used only for teaching about lazy evaluation?

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