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

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Thu Jun 26 14:15:19 EDT 2008


On Jun 26, 2008, at 2:04 PM, David Einstein wrote:

> 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 let*.
> 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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