Re: Attaching context info to an error

[João Távora]

On Wed, Dec 27, 2023 at 6:08 PM João Távora <joaotavora@gmail.com> wrote:

> > Could you give some concrete examples of things you'd (be able to) do
> > with it?

> Just look at anyCL program that uses conditions, there are
> very many of them.  One of them is Snooze [1] which uses them
> to represent HTTP error codes.

To elaborate a little more, Snooze is (I think) a good example
of how 'handler-bind' and 'restart-case' can cooperate to
allow different modes of operation for a HTTP server (or
HTTP REST router, which is what Snooze really is).  You
may want to catch or not catch error conditions, catch or
not catch HTTP conditions, debug these conditions in your
Lisp (or via Emacs with SLY/SLIME), explain these conditions
to the HTTP client verbosely (in developement environments)
, succinctly (in production environments), muffle them,
log them, etc.

The file

  https://github.com/joaotavora/snooze/blob/master/common.lisp

contains the meat and bones of this logic, and

  https://github.com/joaotavora/snooze/blob/master/api.lisp

contains a reasonably well docstring'ed description of the
interface to these facilities.  See the docstrings of
*catch-http-conditions* and *catch-errors*.

Restarts like 'explain-verbosely' and 'explain-succinctly'
are shown to the user when the debugger is popped.  During
development the user can thus interactively control what
gets sent to the client (usually a web-browser in another
window).  Unattended operation of such a server is achieved by
automatically invoking these restarts from handler-bind
handlers.

João