Tags: patch

This is a rough draft of a patch to add two new predicates related to
decoded times: `decoded-time-p', which checks that a value is a decoded
time (as documented in `decode-time'), and
`decoded-time-delta-p', which checks that a value is a time delta (as
documented in `decoded-time-add').

Some questions:

1) Should these functions go in simple.el? I put them there because that
is where the structure definition for decoded-time is. (The definition
does not generate a predicate automatically because it uses :type but
not :named; see Info node `(cl)Structures'.) But at least
`decoded-time-delta-p' might be better off in time-date.el, which is
where `decoded-time-add' is defined.

2) Should `decoded-time-p' also check the weekday slot of decoded times?
See the FIXME comment in the middle of the function: `make-decoded-time'
neither sets this slot nor provides an argument to let the caller set
it. This is apparently intentional: there is a comment in the
definition of `make-decoded-time',

  ;; Do not set decoded-time-weekday or decoded-time-dst,
  ;; as encode-time can infer them well enough when unknown.

but if the slot is not meant to be set I don't understand why it's
there. It would be useful, for iCalendar purposes, to have the weekday
slot automatically calculated from the date values when a decoded time
is constructed. I'm not sure if this use was just not envisioned, or if
there was a more substantial reason not to do it in make-decoded-time.

Hopefully I got the commit message right this time, but please let me
know if that needs tweaking too...

Best,
Richard