When I was at university, we learned a programming language known as Smalltalk. I was rather good at it. [Ironically, making "small talk" is one of the things I do worst IRL! But anyway, back to the topic...] In Smalltalk, there is a wide selection of collection types, all with different facilities and efficiency trade offs. There is bag, set, list, array, ordered list, dictionary, hash table, weak array, etc. A whole menagerie of collection types. However, Haskell only has 1 type of collection: linked lists. (And only single-linked at that.) While other "normal" programming languages spend huge amounts of effort trying to select exactly the right collection type for the task in hand, Haskell programs only ever use linked lists. Why is that, exactly? Does writing software in Haskell magically change the properties of these data structures such that lists become more efficient than all the other types? Or is it that other data structures are only efficient when used with in-place updates? (The latter statement appears to be isomorphic to stating that Haskell programs must necessarily be less efficient than impure ones.) Thoughts?