nm03's phlog talked about using date python packages. I thought I would try
something like that with common lisp. If you install ecl and download
0time-adder.lisp and 0make-your-time.lisp from my 1common-lisp, it should
run happily pretty much everywhere.
ecl --load make-your-time.lisp
will build time-adder.lisp into a-b+c.exe, which has some notion of help
text (-h or --help). I had forgotten that dates are really hard to work with
(is it a leap year? When is the next leap year? How many days in this
month?). I resolved these in a way I think you see sometimes, where you
specify your time delta as being between two dates with every field
defaulting to the current date, and the delta of those first two time/dates
getting added to a third date (default: the day and timezone your computer
thinks it is). When I try the experiment my help text proposes it does this:
(defun alist2seconds (alist)
(multiple-value-bind
(second minute hour date month year day summerp timezone)
(get-decoded-time)
(declare (ignore day summerp))
(apply 'encode-universal-time
(mapcar (lambda (name default) (or (cdr (assoc name alist)) default))
'(second minute hour date month year timezone)
(list second minute hour date month year timezone)))))
(defun seconds2alist (seconds)
(multiple-value-bind
(second minute hour date month year day summerp timezone)
(decode-universal-time seconds)
(declare (ignore day summerp))
(mapcar 'cons
'(second minute hour date month year timezone)
(list second minute hour date month year timezone))))
(defun help-text ()
(print "Try running ./a-b+c.exe with no standard inputs.
Its defaults for a, b and c are the current time.
Then maybe try
/a-b+c.exe <<EOG
((minute . 6) (hour . 3))
((minute . 14) (hour . 1))
EOG
or
/a-b+c.exe <<EOG
((minute . 6) (hour . 3))
((minute . 14) (hour . 1))
((date . 3) (year . 1992))
EOG
"))
