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Comment by vbsteven | Hacker News Reader

I like Kotlins solution for this. If there is only one argument in the lambda/block and the type is clear from the context you don’t have to declare it and you can use the ‘it’ keyword instead.

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Wow, that's splendid! In a sense, it's a very nice dual to "this", which is also a keyword everywhere and not something like $0 or something. I wish more languages had this. Or, it.

If you go back and read the post and linked ticket, that is indeed the original proposal for Ruby, which somehow morphed into positional arguments.

For clarification, it looks like this

  people.filter { it.age > 42 }

Needs more aliases:

  things.filter { its.age > 42 }
  people.filter { their.age > 42 }

;)

Kotlin is great, but I think the "it" syntax was derived from Groovy.

I'm not positive, but Groovy may in turn have been inspired by Perl's $_, as in 'map { $_ + 1 } (1..10);'.

If I recall correctly, the canonical name for that parameter is 'it' as well (though I've never met a Perl programmer that calls it that . . . er, calls it 'it' . . . er, you get the idea).

The first time I saw `it` in a similar construction was in Arc language's aif macro:

        (mac aif (expr . body)
           `(let it ,expr
              (if it
                  ,@(if (cddr body)
                        `(,(car body) (aif ,@(cdr body)))
                        body))))

HN uses it quite a lot, e.g.:

        (defop logout req
           (aif (get-user req)
                (do (logout-user it)
                    (pr "Logged out."))
                (pr "You were not logged in.")))

Anaphoric macros have been used in common lisp since forever.

Thanks for the name! Here's a wikipedia article about them: https://en.wikipedia.org/wiki/Anaphoric_macro

PGs On Lisp details these macros from common lisp. I'm unsure how old they are.

Is it a language feature in that example, or a user defined function/macro? It looks like the latter, but I don't speak Lisp, so I may be wrong.

The latter.

Actually, it can be called a language feature, since it's the macro is defined in arc.arc, the arc lib.

Sounds a lot like Scala's underscore (or at least one usage underscore can mean a few things depending on context). Haven't used Kotlin myself, but I'd agree that sounds like a good thing

And one parameter is 99% of the cases. If you have more than one, you should probably name them anyway.

> And one parameter is 99% of the cases.

In Ruby, the two-parameter hash-iteration case alone is common enough that that's not true.

> If you have more than one, you should probably name them anyway.

In a single line block, I think that often impairs rather than enhances readability.

k, v impairs readability?

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