> How useful is Scala if you don't need to do functional programming with a strong type system?
Functional programming with a strong type system, IMO, has much wider applicability than just the esoteric mathematical abstractions (e.g. Haskell/scalaz) that you're asserting is a niche for Scala.
I can think of many non-scalaz uses of Scala, but even for non-Scala uses, look at Jane Street's evangelism of OCaml (functional + strong type system) for financial systems.
(Note that, personally, while I like the benefits of FP, I admittedly still think in/like aspects of OO, even if just out of habit, so I find Scala's blend particularly nice.)
I think the issue is not that there aren't applications, it's that people just aren't used to looking for them. As an example, let's think of classical geometry. They figured out the area of circles, the volumes of cones, etc without any calculus. If you know the tricks you can figure it out too, or you can just apply a little calculus and it just falls out. I feel that people dismiss the math as unnecessary because they can get by without it, but in reality the math is always there and sometimes provides much simpler solutions.
I've found over the last few years that my thinking has morphed from primarily OO to primarily functional. It isn't for lack of writing OO code, which I do professionally. I find that my brain loves to think in terms of functional transformations on classes of data types.
Suddenly I find myself noticing when things should be expressed as a monad or monoid. I also find myself thinking in type signatures for dynamic languages and silently cursing the language designer who decided a function can return null without warning. I see patterns in my code and find myself wishing I could overload the semi-colon to implement monadic behavior.
Functional programming with a strong type system, IMO, has much wider applicability than just the esoteric mathematical abstractions (e.g. Haskell/scalaz) that you're asserting is a niche for Scala.
I can think of many non-scalaz uses of Scala, but even for non-Scala uses, look at Jane Street's evangelism of OCaml (functional + strong type system) for financial systems.
(Note that, personally, while I like the benefits of FP, I admittedly still think in/like aspects of OO, even if just out of habit, so I find Scala's blend particularly nice.)