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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
+ The psqueues package provides
+ <http://en.wikipedia.org/wiki/Priority_queue Priority Search Queues> in
+ three different flavors.
+ * @OrdPSQ k p v@, which uses the @Ord k@ instance to provide fast insertion,
+ deletion and lookup. This implementation is based on Ralf Hinze's
+ <http://citeseer.ist.psu.edu/hinze01simple.html A Simple Implementation Technique for Priority Search Queues>.
+ Hence, it is similar to the
+ <http://hackage.haskell.org/package/PSQueue PSQueue> library, although it is
+ considerably faster and provides a slightly different API.
+ * @IntPSQ p v@ is a far more efficient implementation. It fixes the key type
+ to @Int@ and uses a <http://en.wikipedia.org/wiki/Radix_tree radix tree>
+ (like @IntMap@) with an additional min-heap property.
+ * @HashPSQ k p v@ is a fairly straightforward extension of @IntPSQ@: it
+ simply uses the keys' hashes as indices in the @IntPSQ@. If there are any
+ hash collisions, it uses an @OrdPSQ@ to resolve those. The performance of
+ this implementation is comparable to that of @IntPSQ@, but it is more widely
+ applicable since the keys are not restricted to @Int@, but rather to any
+ @Hashable@ datatype.
+ Each of the three implementations provides the same API, so they can be used
+ interchangeably. The benchmarks show how they perform relative to one
+ another, and also compared to the other Priority Search Queue
+ implementations on Hackage:
+ <http://hackage.haskell.org/package/PSQueue PSQueue>
+ <http://hackage.haskell.org/package/fingertree-psqueue fingertree-psqueue>.
+ Typical applications of Priority Search Queues include:
+ * Caches, and more specifically LRU Caches;
+ * Schedulers;
+ * Pathfinding algorithms, such as Dijkstra's and A*.