Re: [Haskell-cafe] Dynamically altering sort order

On Fri, Apr 24, 2009 at 19:49, Edward Kmett wrote:

On Fri, Apr 24, 2009 at 5:11 PM, Denis Bueno wrote:

...

Is there an Ord instance that can be dynamically changed in this way?

My first idea is something like this:

   data CompareRecord = CR{ rCompare :: Record -> Record -> Ordering, unCR :: Record }    instance Ord CompareRecord where        compare (CR cmp x) (CR _ y) = cmp x y

where the rCompare field would be a function that is based on the flags passed to the command-line problem.  But this has an ugly asymmetry.  Does anyone have any other ideas?

You can make a safer 'CompareRecord' using 'reflection' from hackage:

This is what I ended up doing and it worked out great. Thanks for the suggestion. Denis