SRFI-19 bug: date->julian-day not inverse of julian-day->date

[Jon Wilson]

Hi,
Take a gander:

guile> (date->string (current-date))
"Wed Jun 27 16:39:42-0400 2007"
guile> (date->string (julian-day->date (date->julian-day (current-date))))
"Wed Jun 27 12:39:43-0400 2007"

Offset by four hours from one another.  Of course, the four hours comes 
from the -0400 time zone.  But clearly one of the two functions is 
taking the time zone into account in a different manner from the other 
function, leading to this discrepancy.

Similarly:

guile> (exact->inexact (current-julian-day ))
2454279.36203873
guile> (exact->inexact (date->julian-day (julian-day->date 
(current-julian-day ))))
2454279.19553665

Nothing changes if I add the timezone specification to the 
julian-dat->date function: (julian-day->date X -14400).  I'm going to go 
look at SRFI-19, and see if I can figure out if this is really a bug or 
a design flaw.  If it is a bug, I'll take a look at fixing it and 
submitting a patch soon.

Regards,
Jon