These same basic characteristics are what made Haskell so attractive to Facebook. The company needed a language that could help engineers write “rules” for identifying spam on its social network.

The quirky functional language Haskell is surprisingly popular for 'weekend' projects, but it won't gain traction at work without a patron ...

Haskell is a 25-year-old programming language that isn't all that popular. But Facebook uses it, and that's a sign of things to come.