James Hague ( Programming in the 21st Century ) points out that we really, really shouldn't be focusing on Optimization. To quote In any modern discussion of algorithms, there's mention of being cache-friendly, of organizing data in a way that's a good match for the memory architectures of CPUs. There's an inevitable attempt at making the concepts concrete with a benchmark manipulating huge--1000x1000--matrices. When rows are organized sequentially in memory, no worries, but switch to column-major order, and there's a very real slowdown. This is used to drive home the impressive gains to be had if you keep cache-friendliness in mind. [...] Linked lists are a worst case, potentially jumping to a new cache line for each element. That's damning evidence against languages like Haskell, Clojure, and Erlang. Yet some naive developers insist on using Haskell, Clojure, and Erlang, and they cavalierly disregard the warnings of the hardware engineers and use ...