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

[ajb at spamcop.net]

G'day all.

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

> Just an idiot-level question: so these "constants" are subject
> to revision, but *how often*?

Good question.  For leap seconds:

  - The data can change no quicker than once every 6 months.
  - The shortest time between changes was 6 months, and the longest
    (so far) was 7 years.
  - The mean change is once every 18 months.
  - You get just under 6 months' notice before a change comes into
    effect.  (No more, no less.)

For most programs, it's the last point that concerns me the most...

> 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?

...because the main cost probably isn't recompiling, it's redeployment.
I don't know about this program in particular, but release cycles longer
than six months are hardly uncommon in our business.

Cheers,
Andrew Bromage