For conditional variables you gave a default value. So then why on earth do you not have an implicit let ? There must be a good reason.
On Sat, Feb 5, 2022 at 12:39 AM Maxime Devos <maximede...@telenet.be> wrote: > Stefan Israelsson Tampe schreef op vr 04-02-2022 om 22:40 [+0100]: > > Anyhow conditional defining vars is a common theme in other languages > > so I think it was kind of natural to implement if as it was done. > > AFAIK no Lisp or Scheme except for Guile < 2.0 implements conditionally > defining local variables (but then I usually only consider Guile Scheme > and the RnRS, so this doesn't mean much). In my experience, I have > never seen a need for conditionally defining a local variable in Scheme > code (if you have a real-world example, please share). > > It also seems impossible to implement this w.r.t. the macro system --- > what should, say, bound-identifier=? do when one of its identifiers is > only conditionally bound? Or for another example: > > If I do > > (define foo 'bar) > (define-syntax foobar > (syntax-rules (foo) > ((_ foo) > (begin (pk "it's a foo!") foo)) > ((_ goo) > (begin (pk "it's not a foo ...") goo)))) > > (define (zebra stripes) > (if stripes > (define foo 'quux)) > (foobar foo)) ;; <--- *** > > then sometimes the 'foo' in '***' refers to the global variable 'foo' > and hence 'foobar' expands to the "it's a foo'.' Sometimes the 'foo' > in '***' refers to the local variable 'foo' (!= the global foo) hence > 'foobar' expands to the "it's not a foo ...". > > However, it's impossible for a macro to expand to multiple things at > once! > > Greetings, > Maxime. >
