[yodsanklai]

It's not really that Haskell is "powerful", but the type system will catch a lot of errors for you and make refactoring much easier.

Also, I wouldn't recommend starting FP with Haskell. It's hard, mostly because of the monads (and laziness can make things more confusing too). Also the syntax which is confusing because indentation is meaningful in some places, but not others.

On the other hand, a language like Scheme is really super easy. Even OCaml is super simple if you stick to the classic ML subset of the language which can take you a very long way. These languages have been using to teach programming to complete beginners. Seriously, OCaml is arguably simpler than Python, and without doubt order of magnitude simpler than C++.

If you're familiar with things like lambda, closures and functions like map or filter in Python, you already know most of what you need to write OCaml code.