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Keith Wright <email@example.com> writes: > > From: Roland Orre <firstname.lastname@example.org> > > > > I think it is time to consider a redefinition of "defined?" to > > make it a special form. > > There is no mention of "special forms" in RnRS, I assume you mean > that you want (defined? x) rather than (defined? 'x). > > > * defined? is still not standardized within the scheme standard > > (thanks Bertrand!) which is a pity as it is an essential procedure > > for everyone who tries to write code which is compatible between > > different interpreters and versions of interpreters. > > The problem is that the standard trys to accomodate the needs of > compilers as well as interpreters. If you think of the program > as a completed text to be compiled once and then executed repeatedly, > then DEFINED? begins to look very odd at best. Why would you want > a dynamic test of whether a variable is defined? Did you not write > the program? Did you forget what you did? _All_ variables are > defined, otherwise they are not variables, but just some identifers > that should not occur in the program at all. I'm not sure if this was the intended usage, but a defined? special form would be useful in a compiled context for compatibility between different scheme implementations for defining what's needed in the case that it's not provided by the implementation, as in, for example: (if (not (defined? string->regexp)) (define (string->regexp s) ...)) I guess SLIB addresses this to some extent by providing separate source code file for each implementation which is written to state more or less what's provided by the implementation & what needs to be loaded from SLIB. -- Harvey J. Stein BFM Financial Research email@example.com