PEP 671: Since it keeps getting asked about, add a para on deferreds (#2661)

Author: Rosuav

pep-0671.rst

@@ -128,7 +128,7 @@ While this does not completely explain all the subtleties, it is sufficient to
 cover the important distinction here (and the fact that they are similar).
 
 
-Interaction with other open PEPs
+Interaction with other proposals
 ================================
 
 :pep:`661` attempts to solve one of the same problems as this does. It seeks to
@@ -141,6 +141,16 @@ of the common cases would no longer need sentinels if the true default could
 be defined by the function. Additionally, dedicated sentinel objects can be
 used as dictionary lookup keys, where :pep:`671` does not apply.
 
+A generic system for deferred evaluation has been proposed at times (not to be
+confused with :pep:`563` and :pep:`649` which are specific to annotations).
+While it may seem, on the surface, that late-bound argument defaults are of a
+similar nature, they are in fact unrelated and orthogonal ideas, and both could
+be of value to the language. The acceptance or rejection of this proposal would
+not affect the viability of a deferred evaluation proposal, and vice versa. (A
+key difference between generalized deferred evaluation and argument defaults is
+that argument defaults will always and only be evaluated as the function begins
+executing, whereas deferred expressions would only be realized upon reference.)
+
 
 Implementation details
 ======================