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

On Mon, 18 Aug 2008, ajb@spamcop.net wrote:

G'day all.

Quoting Bjorn Buckwalter :

...

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.

In this situation, there isn't necessarily any shame in using a top-level unsafePerformIO as long as it's well-hidden:

module AstroData (AstroData(..), globalAstroData) where

data AstroData = AstroData Int

But here my argument about playing around with the Planck constant becomes relevant.