Efficient Amortised and Real-Time Queues in Haskell

Posted on January 15, 2016

A queue is a datastructure that provides efficient—O(1)—operations to remove an element from the front of the queue and to insert an element at the rear of the queue. In this blog post we will discuss how we can take advantage of laziness to implement such queues in Haskell, both with amortised and with worst-case O(1) bounds.

The results in this blog post are not new, and can be found in Chris Okasaki’s book “Purely Functional Data Structures”. However, the implementation and presentation here is different from Okasaki’s. In particular, the technique we use for real-time datastructures is more explicit and should scale to datastructures other than queues more easily than Okasaki’s.

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