[MichaelGG]

Certainly you could wrap up the $ operator into some Ruby method?

[tree_of_item]

Yes, Ruby is Turing complete, but that's missing the point.

The value K provides is the collection of operators like `$` that implement a high level language for the sorts of problems K programmers face.

If you went through and implemented all of those operators in Ruby and only used those instead of things like loops, your code would be "unreadable" to the standard Ruby programmer; essentially you'd be programming in a different language.

[tinco]

Sure, simply do:

    module Enumerable
      def dollar(c)
        map.with_index{|a,i| a == c ? i : nil }.reject{|i| i.nil? }
      end
    end

And then you could do:

    c = a.dollar("\n")

There is of course a reason this dollar method is not a part of the standard library. Its name makes no sense and it's oddly specific, how often would you want the indexes of matches to a character? Most modern languages don't like to work with indexes a lot, and in my day to day work I don't need indexes very frequently either. This I guess is just a thing that these finance/apl people do more often, so they have a specialized standard library.

(So when I said 'a neat way to do $' I meant it has no find_all_with_index method, which would make my implementation much cleaner)

[Widdershin]

Regarding find_all_with_index, you can do:

    .find_all.with_index { |item, index| ... }

[dragonwriter]

except .find_all.with_index passes the index to the predicate block, but still only returns a view of the matching elements from the list.

What I think is being sought is more like:

  module Enumerable
    def find_indices
      each.with_index
          .find_all {|x,_| yield x}
          .map {|_,y| y}
    end
  end