From: mame@...
Date: 2019-09-02T14:00:16+00:00
Subject: [ruby-core:94745] [Ruby master Feature#12543] explicit tail call syntax: foo() then return

Issue #12543 has been updated by mame (Yusuke Endoh).


I don't like `--tail-call-optimization-off`.  I will not specify the option, see an omitted backtrace, and then I must re-run my code with the option.  It is not an easy-to-debug language for me.

And I have another concern.  If tail call optimization is on by default, some people will strongly depend on it.  For example, someone may write:

```
def main_loop
  socket = server_socket.accept
  ...
  main_loop
end
```

This code will break when `--tail-call-optimization-off` is specified.

So, I think it should be off by default, and it would be good to allow to write:

```
def main_loop
  socket = server_socket.accept
  ...
  return and main_loop # explicit tail call
end
```

----------------------------------------
Feature #12543: explicit tail call syntax: foo() then return
https://bugs.ruby-lang.org/issues/12543#change-81362

* Author: mame (Yusuke Endoh)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
How about introducing a new syntax for tail call?

```
def foo()
  foo()
end
foo() #=> stack level too deep
```

```
def bar()
  bar() then return
end
bar() #=> infinite loop
```

* no new keyword (cf. `goto foo()`)
* no conflict with any existing syntax
* an experimental patch is available (attached)
* no shift/reduce nor reduce/reduce conflict in parse.y

-- 
Yusuke Endoh <mame@ruby-lang.org>

---Files--------------------------------
then_return.patch (9.18 KB)


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