Scala allows underscores, and sequential underscores refer to the next element, so you can do e.g.

    list(1, 2, 3, 4).reduce(_ + _) == 10

Doesn't that make the parameter anonymous, though? Can you println that _ and see the value of the current element?

Use a function that prints then returns its parameter:

  list(1, 2, 3, 4).reduce{print(_) + _} == 10

Use it if you or your language hasn't defined such a function:

  list(1, 2, 3, 4).reduce{it:= _; println(it); it + _} == 10

In fact, any name for it will do.

Yeah, that's the tradeoff–gain the ability to work with multiple parameters but lose the ability to reuse a single one.

And Haskell uses operator sections: (==0) would be similar to { it == 0 }. Alas, the section syntax get a bit cumbersome when you want to compose two or more of them, like in this translation of your example:

    filter ((0==) . (%2)) [1, 2, 3, 4]

so does LiveScript