Stephan Friedrichs wrote:
I'm sorry it took me so long to respond!
No worries :)
In conclusion: the ordering policy stuff should not be part of
Data.Heap, this is a job for Data.Ord.
This sounds really useful. How about you propose
this to the base-package maintainers? :)
What, me? :D
Where? :)
Proposals for the base package go to [EMAIL PROTECTED] . A
proposal is a darcs patch + a deadline. Unfortunately, ghc 6.8.* isn't
yet available on Macports, I'd have to install 6.6.1 again on my wiped
disk to get a haskell compiler and darcs.
I'm currently leaning towards code like
data OrdBy p a = OrdBy { unOrdBy :: a }
instance Eq a => Eq (OrdBy p a) where
(==) = (==) `on` unOrdBy
data Reverse
type Reversed a = OrdBy Reverse a
instance Ord a => Ord (OrdBy Reverse a) where
compare = flip $ comparing unOrdBy
and probably another example for custom orderings. Do you now a good one?
I'm not so happy about the names. In particular, I don't like unOrdBy ,
too much cAmelCase. Any other ideas? Maybe
data Rearrange p a = Rearrange { unRearrange :: a }
data ReOrd p a = ReOrd { unReOrd :: a }
But I guess it can't be helped and it's not too bad either.
The class constraint
Ord (OrdBy p a) =>
will be common in user code, but it's a bit bulky for my taste. However,
its main problem is that it's not Haskell98 :( A multi-parameter class
(just like in the original heap-0.1)
class OrdPolicy p a where ...
instance OrdPolicy p a => Ord (OrdBy p a) where ...
is shorter but not H98 either. The name could be a mot juste, too.
class Rearranged p a where ...
class Ord' p a where ...
class OrdBy p a where ... -- clashes with the name of the type
Regards,
apfelmus
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