> A lot of stuff to get your head around. There are complex topics from category theory to metaprograming. Sure you can ignore it - until you want to use a web framework that uses those concepts, then it's on you.

I'm convinced this is just FUD. Every language's main web framework has a bunch of complex concepts to learn - if you want to use Rails you're going to have to learn about ActiveRecord, metaclasses, whatever it is that rails uses for routing. By the time you've got productive in an enterprise-scale codebase, you've learnt just as much as if you were using Haskell - the only difference is that the knowledge is less transferable.