What are some impressive examples of functional code?

Question

I'm getting a bit tired of having to code explicitly for multicore if I want more speed, particularly when I'm just writing a one-off script. My dev box already has 8 cores and that number is going up a lot faster than the clock speed. Functional languages seem to offer a potential escape hatch, but I haven't put in the effort to master one of them yet.

I'd love to see some sample chunks of real-world code that are much better and/or more parallelizable than non-functional alternatives. I'm not picky about the language -- I'm more interested in the concepts.

Thanks!

Answer 1

How about MapReduce? It's incredibly parallelizable and even though it's not implemented in functional languages as far as the paper goes, it's inspired by Lisp's map and reduce.

Answer 2

Your question is asking for material right at the state of the art. I think your best introduction to this field, with examples, is the book Implicit Parallel Programming in pH by Nikhil and Arvind.

Answer 3

There's an extended example of a text indexer/searcher using mapreduce in Chapter 20 ("Programming Multi-core CPUs") of Programming Erlang. I don't know how impressive that is, but it looks like code mortals can write.

Answer 4

This (long, but very good) video gives both an intro to F# and a compelling demo of how easy it is to parallelize code in the language:

http://channel9.msdn.com/pdc2008/TL11/

Answer 5

LINQ is a nice example of functional programming in mainstream languages. Reified code and monads? In MY C#? :) Anyways, w.r.t. threading, there's mention of Parallel LINQ. By using immutability and higher order functions (and Expression, perhaps), libraries can parallelize things for us.

And another link to F# with async workflows. What's impressive is the ability to take sync code, and with a few small annotations turn it into async code. The code retains a lot of the imperative qualities you might be using. You don't have to completely change things to take advantage of this; the compiler via handles it all.

Answer 6

Purely Functional Data Structures (long PDF), by Chris Okasaki.

Answer 7

A teacher of mine used to joke that the greatest example of functional code is the code that is not written.