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is it a new data type?

This page is part of the web mail archives of SRFI 39 from before July 7th, 2015. The new archives for SRFI 39 contain all messages, not just those from before July 7th, 2015.

A few questions/comments:

Are parameters a new data type? This srfi does not define any procedures on parameters, so in that sense they are not. However, implementations may want to define such procedures, in which case having a predicate |parameter?| would be essential. Note however that r5rs compliance would still require |procedure?| to return #t for parameters.

What happens when the converter procedure returns more than once, e.g. when a continuation captured inside it is invoked?

It would be useful for (<parameter> <value>) to return the existing value since a lot of uses of dynamic parameters are of the pattern:
 * get parameter value -> old_value
 * set parameter value
 * do something
 * set parameter value to old_value
Having a setter that returns the existing value allows elimination of the first step.