[ruby-core:96500] [Ruby master Feature#15973] Let Kernel#lambda always return a lambda

[daniel@dan42.com]

Issue #15973 has been updated by Dan0042 (Daniel DeLorme).


> one of the key points of Ruby's attractiveness is how far it goes to reduce boilerplate in a logical and humane way. There is a non-neglectible gap between "human" consistency and "computer" (formal) consistency.

+1, very much. I'm glad there's still someone who cares about usefulness over ["consistency"](https://www.google.com/search?q=ralph+waldo+emerson+quote+foolish+consistency)

Converting a proc to a lambda is very useful for DSLs. And generally speaking it's empowering to programmers. Maybe a bit dangerous, but I can take care of myself. I really don't need or want to be "protected" from powerful yet "unexpected" behaviors. This ticket was about making `lambda` always return a lambda; at which point did it become about preventing this from happening?

I understand there's many who are emotionally invested into making ruby stricter and easier to implement/optimize, but at least there should be good alternatives for what the proc->lambda conversion allows.

For DSLs:

```ruby
#a block is specified, and this DSL is documented to have lambda semantics, so we need to convert the proc to lambda
register_lambda(:xyz) do |x,y,z|
  return x+y+z
end

#or a pretty syntax to pass a lambda as a block
register_lambda(:xyz)->(x,y,z) do
  return x+y+z
end

#because this is ugly, honestly
register_lambda(:xyz, &->(x,y,z) do
  return x+y+z
end)
```

Or what about:

```ruby
block = proc{ |x,y,z=1| }
block.parameters #=> [[:opt, :x], [:opt, :y], [:opt, :z]]
                 # yes I know that all params are optional in a proc,
                 # but I wanted to know which have a default value and which don't
lambda(&block).parameters #=> [[:req, :x], [:req, :y], [:opt, :z]]
                          # this tells me what I wanted to know in a simple and easy way
```

Beyond the argument that this is dangerous (yes it is), there's also the fact that, used wisely, this is sometimes **useful**.

> it's really awkward and hard to check if the block is literal or not (considering lambda can be alias-ed).

Then wouldn't it be really simple if all blocks were converted to lambdas regardless of being literal or not? KISS.

----------------------------------------
Feature #15973: Let Kernel#lambda always return a lambda
https://bugs.ruby-lang.org/issues/15973#change-83432

* Author: alanwu (Alan Wu)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 2.8
----------------------------------------
When Kernel#lambda receives a Proc that is not a lambda,
it returns it without modification. l propose to change `Kernel#lambda`
so it always returns a lambda.

Calling a method called lambda and having it do nothing in effect is
not very intuitive.

https://github.com/ruby/ruby/pull/2262

Judging from marcandre's investigation here: https://bugs.ruby-lang.org/issues/15620#note-1,
changing the behavior should not cause much breakage, if any.


This also happens to fix [Bug #15620]



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