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

19 Aug 2008

      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

         -- You really don't want this function inlined.  You also
         -- really don't want this function to be polymorphic.
     {-# NOINLINE globalAstroData #-}
     globalAstroData :: AstroData
     globalAstroData = unsafePerformIO $ do
         d <- return 42    -- Or whatever
         return (AstroData d)

Cheers,
Andrew Bromage

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

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