On 4 July 2012 14:54, Patrick Palka
On 7/4/2012 5:02 AM, Thomas Schilling wrote:
I'm surprised that these functions already exists in Data.Map. What are the use cases?
One can use the indexing functions to retrieve a random element from the container, or to random-shuffle a container in n log n time.
OK, that seems like a reasonable use case. The existing documentation is lacking, though. For example, the above use case requires that: 0 <= index < Map.size map It's also not specified that the index refers to the index in the sorted sequence. Of course, that problem here is that "Ord" -- which is really an implementation detail -- becomes part of the specified properties of a Map/Set. E.g., the same function for HashMap probably wouldn't make that guarantee. I.e., what are the properties of these functions? Do we have: - findIndex a set `compare` findIndex b set ==> a `compare` b - findIndex a set == findIndex a (Set.toList set) - ... Hoogle is down (along with haskell.org), ATM, so I can't look up the proper list functions.