[Haskell-cafe] Re: Reader monad, implicit parameters, or something else altogether?

[Bjorn Buckwalter]

Richard A. O'Keefe <ok <at> cs.otago.ac.nz> writes:

> Just an idiot-level question: so these "constants" are subject
> to revision, but *how often*?  What is the actual cost of
> recompiling and using them *as* constants, compared with the
> cost of rereading the stuff every time you run the program and
> passing it around?

My apologies but I kind of lost track of this thread after the initial helpful
replies and didn't follow up diligently on what went only to haskell-cafe (which
I don't follow regularly) and not to my inbox. 

In case you are still curious an example of data that changes frequently is
Earth orientation parameters (of which the leap seconds which Andrew elaborated
on are one). These include e.g. the difference between UT1 and UTC (UT1-UTC)
which is necessary to accurately relate the position and orientation of e.g. a
ground based observer to an object in inertial space. UT1-UTC is continuously
monitored with new observed an predicted values being published daily.
Additional parameters and their update frequencies are listed at [1] and
available compiled and with some documentation at [2].

[1] http://www.celestrak.com/SpaceData/EOP-format.asp
[2] http://www.celestrak.com/SpaceData/

A piece of software precessing e.g. satellite orbit observations would ideally
use the latest Earth orientation parameter data without requiring a recompile
for each day.

Thanks,
Bjorn