Used humorously as a random parameter on which something is
said to depend. Sometimes implies unreliability
of whatever
is dependent, or that reliability seems to be dependent on
conditions nobody has been able to determine. "This feature
depends on having
the channel open in mumble mode, having
the
foo switch set, and on
the phase
of the moon."
See also
heisenbug.
True story: Once upon a time there was a
bug that really did
depend on
the phase
of the moon. There was a little
subroutine that had traditionally been used in various
programs at
MIT to calculate an approximation to
the moon's
true phase.
GLS incorporated this routine into a
Lisp
program that, when it wrote out a file, would print a
timestamp line almost 80 characters long. Very occasionally
the first line
of the message would be too long and would
overflow onto
the next line, and when
the file was later read
back in
the program would
barf.
The length
of the first
line depended on both
the precise date and time and
the length
of the phase specification when
the timestamp was printed, and
so
the bug literally depended on
the phase
of the moon!
The first paper edition
of the Jargon File (Steele-1983)
included an example
of one
of the timestamp lines that
exhibited this bug, but
the typesetter "corrected" it. This
has since been described as
the phase-
of-
the-
moon-bug bug.
[
Jargon File]
(1995-02-22)