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>>>>> "Roland" == Roland Orre <email@example.com> writes: Roland> I think it is time to consider a redefinition of "defined?" to Roland> make it a special form. I'm not sure this is really an objection, but if "defined?" becomes a special form, it becomes more difficult to check if a variable holds a symbol that is defined. Roland> * defined? is still not standardized within the scheme standard Roland> (thanks Bertrand!) which is a pity as it is an essential Roland> procedure for everyone who tries to write code which is Roland> compatible between different interpreters and versions of Roland> interpreters. Perhaps this is a good place for a SRFI. Keith> Why would you want a dynamic test of whether Keith> a variable is defined? Did you not write the program? In reasonably large systems where stuff is dynamically loaded and unloaded, you didn't write the program. It's being written as it runs. Without a procedure like defined? it is difficult to query the state of the system when the program adds new code. Keith> The Garbage Collector cleans up storage. Long running Keith> applications do not typically use up variables as they run; Long running interactive applications and long running hardware control applications often do. It's very nice to be able to completely remove all traces of some code from a system. Keith> The only use I see for Keith> UNDEFINE is during interactive development when you Keith> discover you have made a boo-boo. Even then it doesn't do Keith> much that couldn't be done by (define boo-boo #f). For certain types of applications polution of the namespace is as bad as unclaimed memory. And, in an interpreter a defined symbols do require space even if it they are not attached to a value. Keith> I see DEFINED? as analogous to EVAL. For certain special Keith> purposes (_not_ in ordinary applications) it is useful to Keith> treat lists of symbols as programs. You're "special purpose" may be my "ordinary". That's not an argument to exclude "DEFINED?". Cheers, Clark