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Re: datum comments of sweet-expressions

This page is part of the web mail archives of SRFI 110 from before July 7th, 2015. The new archives for SRFI 110 contain all messages, not just those from before July 7th, 2015.

On Fri, 12 Jul 2013 10:10:43 -0400, John Cowan <cowan@xxxxxxxxxxxxxxxx> wrote:
> I think the EMPTY tag works
> better.  However, I think the habit of using conses as unique tags
> just makes debugging output hard to decipher.  I much prefer this style:
> (define foo-tag (string-copy "foo"))
> This is guaranteed to return a unique object.

Interesting. I've tended to use conses as unique tags because that ports to
essentially every Lisp in existence, past and present.
Kind of weird to use a string this way, really.

But we'll only use "eq?" on it, so that should be fine.
Okay, I'll give that a whirl.

>  In Common Lisp, this
> is spelled:
> (defconstant foo-tag (copy-seq "foo"))

In Common Lisp I think I'd use this instead:
  (make-symbol "empty-values")
Mentally I think the empty tag is more like a special symbol than a string.
Of course, I can't use Scheme's string->symbol the same
way, because that would *reuse* a symbol of the same name.

--- David A. Wheeler