[plt-scheme] What are the semantics of optional variables?

From: David Einstein (deinst at gmail.com)
Date: Thu Jun 26 14:04:18 EDT 2008

If I may join Circular function in asking annoying questions (co-sinning as
it were), what exactly are the semantics of optional variables?
It appears from experiment that they are evaluated sequentially in
environments containing the previously declared parameters, kind of like
In fact, it appears that evaluation of optional parameters can safely[*]
mutate earlier optional and non-optional parameters.

[*] but not necessarily sanely.  I've probably been writing too much R code
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