[ruby-core:103315] [Ruby master Feature#17786] Proposal: new "ends" keyword

Issue #17786 has been updated by jzakiya (Jabari Zakiya).


The process to implement this proposal are actually much simpler than you make it out to be.

This would be perfectly syntactically legal code.

```
A.class_eval do
  define_method :b do
    c do
      d do
        e
  ends

  def c
  end
end
```
It would be expanded to

```
A.class_eval do
  define_method :b do
    c do
      d do
        e
      end
    end
  end

  def c
  end
end
```

So in your code example, starting at the beginning (outer most layer) the parser starts counting how many ``things`` (module|class|method names, loops, conditionals, etc) are currently open (haven’t been resolved as terminated). At some point, it counts the last thing that needs to be resolved. When it encounters the first ``end`` it tries to resolve it with the last (highest count) ``thing`` that’s still open. It then continues backing up the tree count, until all the unresolved ``things`` count is zero.

So now the source code AST is fully resolved, and w|should look just like normal. This is what is then feed to the compiler. But there has to be a way to know how many things need to be terminated and how many are still open.

I would assume for Ruby, the parsing stage is separate from compilation. You have to go through some process to turn raw source code, through whatever number of stages of processing, to format it into runtime code.

So in my mind, all the parser has to do is account for all open ``things``, and start resolving them from the most inner layer ``things`` back out to the outer layers, until every ``thing`` is resolved.

This should be a much simpler|easier process to do than what Python does, because it has whitespace dependencies, whereas Ruby doesn't care. All Ruby would have to do is go down, and back up, the parsing tree.

So in the big picture, you don't have to care much about what the ``thing`` is, you just have to keep track of how many there are, because all you're going to first do is put the source code in equivalent standard format with expanded out ``end`` statements, which can then be processed as usual.

----------------------------------------
Feature #17786: Proposal: new  "ends" keyword
https://bugs.ruby-lang.org/issues/17786#change-91404

* Author: jzakiya (Jabari Zakiya)
* Status: Open
* Priority: Normal
----------------------------------------
I'm submitting this in the same spirit that ``endless methods`` was, to promote and produce more concise and easier to write|read code.

**Proposal**
This is a proposal to introduce a new keyword ``ends`` (or ``endall``) as a terminal point to resolve the end of nested ``loops|conditionals``.

**Why**
It's a common code occurrence to have multiple levels of loops and/or conditionals, which require separate ``end`` keywords to designate their
termination points. The ``end`` statements themselves are merely for syntactic purposes.

It would be a benefit to programmers, and code readers, to be able to produce|read more concise code, by reducing the ``code noise`` of these
nested multiple ``end`` keywords with a shorter|cleaner syntax.

Thus, I propose creating the keyword ``ends`` as a shorter|cleaner syntax to replace having to write multiple ``end`` keywords.

**Example**

Below is an example of real code which performs nested loops. With "standard`` format it looks like this.

```
def render(scene, image, screenWidth, screenHeight)
  screenHeight.times do |y|
    screenWidth.times do |x|
      color = self.traceRay(....)
      r, g, b = Color.toDrawingColor(color)
      image.set(x, y, StumpyCore::RGBA.from_rgb(r, g, b))
    end 
  end 
end
```

However, from the point of view of the parser, these are all legal|equivalent.

```
def render(scene, image, screenWidth, screenHeight)
  screenHeight.times do |y|
    screenWidth.times do |x|
      color = self.traceRay(....)
      r, g, b = Color.toDrawingColor(color)
      image.set(x, y, StumpyCore::RGBA.from_rgb(r, g, b))
    end     end         end     end end end
  end         end       end
end             end     end
```

This proposal would allow this type of code to be writtn as:

```
def render(scene, image, screenWidth, screenHeight)
  screenHeight.times do |y|
    screenWidth.times do |x|
      color = self.traceRay(....)
      r, g, b = Color.toDrawingColor(color)
      image.set(x, y, StumpyCore::RGBA.from_rgb(r, g, b))
ends
```
**Pros**
1) code conciseness
2) better readability
3) no whitespace dependencies
4) no conflict with legacy code
5) attractice to people coming from Python|Nim, et al

**Cons**
No technical implementation restrictions I can think of.
Maybe alternative name (endall)?

Thanks for consideration.




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