Bitmapped vector tries vs. arrays

[Timon Gehr]

On 12/18/2011 04:48 PM, bearophile wrote:
> Andrei Alexandrescu:
>
>> http://www.reddit.com/r/programming/comments/nddlj/extreme_cleverness_functional_data_structures_in/
>
> You need to be registered to download the PDF slides :-(
>
> Scala language seems rather compact and powerful to define such data structures. The function balance() at 24.21 to balance red-black trees using just pattern matching is quite nice, despite being a bit long.
>
> But I don't know what those operators like  +A>:<:   mean.
>
> Bye,
> bearophile

+A (-A) means A only occurs in covariant (contravariant) positions, the 
other two are used for constraints, where >: means supertype-of and <: 
means subtype-of.