In Real World Haskell, there is a section titled ‘Life without arrays or hash tables’ where the authors suggest that list and trees are preferred in functional programming, whereas an array or a hash table might be used instead in an imperative program.
This makes sense, since it’s much easier to reuse part of an (immutable) list or tree when creating a new one than to do so with an array.
So my questions are:
- Are there really significantly different usage patterns for data structures between functional and imperative programming?
- If so, is this a problem?
- What if you really do need a hash table for some application? Do you simply swallow the extra expense incurred for modifications?
The book Purely Functional Data Structures covers your questions in depth, and includes a great mix of theory and implementations primarily in ML – the appendix also contains Haskell implementations so you should be able to follow along with a bit of extra page turning. It is a pretty good (though difficult in parts) read if you are really interested in a thorough answer to your questions. Having said that I think ephemient gave a superb short answer.
edit: Steven Huwig provided a link to the thesis that the book started as. While I haven’t read through it the only big thing missing (judging from the table of contents) are the Haskell implementations.