[MaxBarraclough]

> it can be hard to determine what aspects of a given library are the encoding and which parts are the fundamental ideas if you haven't seen the ideas used in well-suited language

That's a good point. Using a proper functional programming language doesn't just enable FP ideas (you can't fake a feature like implicit capture of variables), it may also clarify them by reducing baggage.

> I found `functools.reduce(function, iterable, initializer)` significantly more opaque than `foldl :: (b -> a -> b) -> b -> [a] -> b` because the type signature makes it clear what sort of functions are suitable for use as the first argument.

I suspect you're just a better Haskell programmer than me (I've only ever dabbled), but I find the big-mess-of-arrows syntax to be pretty confusing compared to a simple tuple of descriptively named identifiers.

Perhaps related to this: I don't see the practical appeal of currying. Even C++ supports the 'bind' pattern just fine - http://www.cplusplus.com/reference/functional/bind/#example