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Comment by kmiroslav | Hacker News Reader

Groovy and Kotlin use the implicit "it" parameter for lambdas that take just one parameter, which is very convenient:

    listOf(1, 2, 3, 4).filter { it % 2 == 0 }

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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?

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

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.

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

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