Heinrich Apfelmus wrote:
Job Vranish wrote:
I've been in a situation a lot lately where I need to keep a collection of
values, and keep track of them by a persistent index.
module Store (Key, Store, empty, add, delete, lookup) where
newtype Key = Key { int :: Int }
empty ::
Thanks for all the input! :)
My current code (unfinished) is here:
http://github.com/jvranish/IndexedCollection/tree/master
but I think I'll shorten the names as you suggest. (and add some strictness
to availableKeys)
I also added an extra phantom type parameter to the collection (and key) so
On Aug 21, 2009, at 5:11 PM, Job Vranish wrote:
I also added an extra phantom type parameter to the collection (and
key) so that I can prevent keys from being used on different
collections even if they hold elements of the same type.
I have the impression that this requires explicit type
It only requires type annotations on your uses of empty (as that is the only
way to construct a collection). The phantom type sticks to everything after
that.
If you don't care to add a signature then things still work just fine, you
just won't be prevented from using indexes from the wrong
Job Vranish wrote:
I've been in a situation a lot lately where I need to keep a collection of
values, and keep track of them by a persistent index.
data IndexedCollection a = IndexedCollection {
nextKey :: Int,
availableKeys :: [Int],
items :: IntMap a
} deriving
