Question

I have the following (imperative) algorithm that I want to implement in Haskell:

Given a sequence of pairs [(e0,s0), (e1,s1), (e2,s2),…,(en,sn)], where both “e” and “s” parts are natural numbers not necessarily different, at each time step one element of this sequence is randomly selected, let’s say (ei,si), and based in the values of (ei,si), a new element is built and added to the sequence.

How can I implement this efficiently in Haskell? The need for random access would make it bad for lists, while the need for appending one element at a time would make it bad for arrays, as far as I know.

Thanks in advance.

Answer 1

I suggest using either Data.Set or Data.Sequence, depending on what you’re needing it for. The latter in particular provides you with logarithmic index lookup (as opposed to linear for lists) and O(1) appending on either end.