Re: Is gentemp or gensym "safe"?

[Martin Grabmueller]

> From: Rob Browning <address@hidden>
> Date: 24 Apr 2001 15:02:58 -0500
> 
> I'm nearly finished implementing srfi-11 using define-macro, and while
> let*-values was fairly easy to implement elegantly, let-values is
> somewhat uglier, and I need to create safe temporary values in the
> expansion.  Is that possible with gensym or gentmp?

They are not really safe, but see below.

> The documentation for gentemp seems off, indicating it takes 2
> optional args, when in fact it takes only one.

For me it does take 0 to 2 args.

guile> (gentemp)
t0
guile> (gentemp "foo")
foo1
guile> (gentemp "foo" '#(() () ()))
foo2

>  Also, if you specify a prefix to gensym, it starts generating very
> simple symbols.

The symbols are always very simple.  Whether that's a good idea, I am
not sure.

guile> (gensym)
g0
guile> (gensym "foo")   
foo1

>  These are guaranteed not to conflict with the existing bindings,
> right?

The implementation of gentemp looks like it is avoiding already
defined symbols, but it obviously doesn't.  What's wrong here?

guile> (gensym "foo")   
foo1
guile> (gensym "foo")
foo2
guile> (define foo3 1)
guile> foo3
1
guile> (gensym "foo") 
foo3

Regards,
  'martin