Andrew Coppin wrote:
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?
You seem to only bee looking at 2 line long functions in Haskell. Partly the use of lists comes from the fact that iterating over a sequence of values is a very very common operation (the C++ STL's forward iterators; java has 'foreach' syntax). Haskell's lazy list captures this idiom, and the compiler can apply useful optimizations (deforesting). But Haskell does comes with many data structures that most programs use: http://haskell.org/ghc/docs/latest/html/libraries/ documents what comes with GHC: Data.ByteString ( new and very efficient operations ) Data.Sequence ( based on finger trees ) Data.Tree Data.HashTable Data.Map Data.IntMap Data.Set Data.IntSet Data.PackedString Data.Queue Data.Graph For arrays there are the immutable: Data.Array Data.Array.Diff (secretly mutates for efficiency) Data.Array.Unboxed And mutable arrays: Data.Array.IO (boxed and unboxed) Data.Array.ST (boxed and unboxed) And for interfacing with the world: Foreign.Marshal.Array Data.Array.Storable http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Data%20Structu... lists "collections" and "Edison" which both aim to implement a family of collections. And http://haskell.org/haskellwiki/Applications_and_libraries/Data_structures has more information on the wiki. -- Chris