Thomas Schilling wrote:
Levi Stephen wrote:
I'm was wondering how most people work during when designing a functional program. Do you create data structures/types first? Do you work from some type signatures?
But there's a third thing that you can do, other than start implementing: think about the laws/properties that should hold. That's not always simple, in fact, it rarely is.
Yes, the classic approach: systematically derive programs from their specification. The classic paper on that is Paul Hudak. The Design of a Pretty-printing Library. http://citeseer.ist.psu.edu/hughes95design.html with a follow-up Philip Wadler. A prettier printer. http://decenturl.com/homepages.inf.ed/wadler-98-prettier-printer The man who derives all his programs from specification is Richard Bird. You may want to have a look at his recent sudoku solver Richard Bird. A program to solve Sudoku. Slides: http://icfp06.cs.uchicago.edu/bird-talk.pdf where he starts with an apparently correct but hopelessly slow specification and transforms it into a blazingly fast one. His introduction to Haskell Richard Bird. Introduction to Functional Programming using Haskel (2nd edition). http://decenturl.com/amazon/bird-introduction-functional emphasizes the classic style, too. You may think "this is all nice, but my problem is too 'soft' for mathematical laws and properties and such". Well, if you don't search, you won't find. Here's an example for a "soft" problem domain: Simon Peyton Jones, Jean-Marc Eber, Julian Seward. Composing contracts: an adventure in financial engineering. http://decenturl.com/research.microsoft/spj-financial-contracts Of course, the laws "of nature" governing your problem domain may be hard to find, so it may be worth to "just implement" and let some "law intuition" guide you. Well-known example: darcs. Regards, apfelmus