All, I have a growing amount of astrodynamics code that relies on various physical "constants". The problem with these so called "constants" are that they either aren't really constants or aren't well known. An example is the leap second table (see Data.Time.Clock.TAI). I'd like to be able to fetch current values of these constants at runtime and make them accessible to my astrodynamics functions by some means. To clarify, once initialized the constants will be considered constant for the remainder of the program. I'd store the constants in a data structure along the lines of:
data AstroData a = AstroData { mu_Earth :: GravitationalParameter a , leapSeconds :: LeapSecondTable }
I would like to know if there is any consensus on what is the best way to make such a data structure accessible in pure functions. Passing it explicitly would be a mess. It seems that two options are to use either a Reader monad or implicit parameters. Using a Reader monad is straight forward enough though it requires writing/converting code in/to monadic style and adds some clutter to the formulae. It seems implicit parameters could be cleaner but I've seen them referred to as everything from evil to "just what you need" and rendering the Reader monad obsolete... What do you people recommend? Thanks, Bjorn Buckwalter