Functional languages: Real-life Examples

Question

Do functional languages bring anything in the resolution of everyday business problems?

Are there any successful projects that have been implemented using a functional language (ideally with a published test case)?

Answer 1

There are quite a few listed on Functional Programming in the Real World. From the site:

The main criterion for being real-world is that the program was written primarily to perform some task, not primarily to experiment with functional programming.

Answer 2

The Xen hypervisor is at base, implemented in OCAML; and Erlang is deployed in ultra-high reliability telephony systems (the ones that have zero down-time over periods of years).

Answer 3

One implementation of Perl 6, Pugs, is written in Haskell, but it has largely given way to the standard Rakudo Perl implementation.