[asdf-devel] :DBG

Ken Tilton kentilton at gmail.com
Mon Nov 18 09:24:30 UTC 2013

packages do not obviate the need for prefixes, essential to code
readability. And then we do need packages, the worst thing that ever
happened to lisp..

but the problem here originates from a desire to share a debug hack, so the
solution prolly involves a way to share debug hacks. Could be a fun
project. We could call it :dbg.


On Mon, Nov 18, 2013 at 2:56 AM, Stas Boukarev <stassats at gmail.com> wrote:

> Faré <fahree at gmail.com> writes:
> > In ASDF, I introduced a macro :DBG (in uiop/utility.lisp).
> > Yes, it's in the keyword package. Why?
> > Because it's the one and only macro I want to be accessible from
> everywhere
> > without a prefix, yet without modifying existing defpackage forms to make
> > it accessible — because it's only used temporarily for debugging.
> >
> > :DBG is a macro for print-debugging. The syntax is
> >    (:DBG tag forms... last-form)
> > The semantics is that if tag is true, print the tag, then for each
> > form, write its source and its values; return the values of the last
> > form. If tag is false, just evaluate the last form and return its
> > values. (Tag is typically a constant keyword or string, identifying
> > the point where values are printed.)
> > The expansion is rather space and time efficient, as far as the
> > semantics permit.
> >
> > I find :DBG soooo useful for print-debugging. I've seen tens of
> > variants of it, but every time with something not quite right in the
> > syntax, semantics or implementation. I just wanted one variant that
> > got everything right, and make it ubiquitous. Because when you need
> > it, you need it now, and there's no time to modify things to load an
> > additional library. And when you're done, you want minimal cleanup,
> > too: just delete the form, except maybe keep the last subform.
> >
> > Previously, I was using (uiop:uiop-debug) from uiop/utility which
> > allows you to load a magic file of your choice that defines a debug
> > mode. The default one I provided was mine, which define :DBG as DBG in
> > your current package (thereby avoiding symbol import issues). But that
> > still adds a new definition everytime and an extra line or form to
> > cleanup.
> >
> > I was recently convinced that using the keyword package instead makes
> > perfect sense: on the one hand, that's using a shared namespace that
> > it is polite to not pollute, but on the other hand, such a temporary
> > print-debugging macro the only use case I imagine of otherwise wanting
> > something to be immediately accessible without package prefixing yet
> > without modifying the package definition form.
> >
> > It's still time to remove that macro before the next release, but I
> > believe it's the right thing to include it, and maybe some of you will
> > agree with me and start using it, if not from the yet unrelease ASDF
> > 3.1.1, perhaps from a copy in your .sbclrc.
> Thanks for breaking my :dbg macro.
> --
> With best regards, Stas.
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