I'm a big Haskell fan (it was my favorite language before discovering Nim), but here's my personal list of Nim advantages over Haskell:

    - Predictable performance (lazy evaluation is problematic)
    - Easy to achieve high performance
    - Easier to read, even for non-specialists
    - I'm much more productive in it
    - Multi-paradigm: Nim is mostly imperative, but OO and functional can be mixed as well.

http://hookrace.net/blog/conclusion-on-nim/