On 01:08 Sun 05 Dec , Serguey Zefirov wrote:
Why TypeRep does have equality and doesn't have ordering?
It would be good to have that.
I think the problem is, that it's hard to give an ordering that stays the same for all runs of your program. If you don't need this property you could use typeRepKey to give an instance as follows: instance Ord TypeRep where compare t1 t2 = compare (unsafePerformIO (typeRepKey t1)) (unsafePerformIO (typeRepKey t2)) I know it's not good style to use unsafePerformIO, but if you look at how typeRepKey is implemented I think it should be okay: typeRepKey :: TypeRep -> IO Int typeRepKey (TypeRep (Key i) _ _) = return i (The Eq instance also uses the key for comparison.)
Right now when I have to order two type representations I convert them to string and then compare. This is somewhat inefficient and not quite straightforward.
The implementation above should be efficient but should not be used when data between multiple runs since the ordering may change. Andreas