Issue #12809 has been updated by Akira Tanaka.

Status changed from Assigned to Rejected

Current behavior is intentional design.

If "lambda" change the lambda-ness of the given block,
the author of "proc { |a| a * 2 }" can not know how the block is interpreted.
This is what the design try to avoid.

Rather, it may be possible to raise error on "lambda" with non-lambda proc object.
This is different issue, though.

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Bug #12809: passing a proc to Kernel#lambda does not create a lambda
https://bugs.ruby-lang.org/issues/12809#change-62154

* Author: Sylvain Joyeux
* Status: Rejected
* Priority: Normal
* Assignee: Akira Tanaka
* Target version: 
* ruby -v: 2.0.0-p643, 2.1.9, 2.2.5, 2.3.1p112, 2.4.0preview2
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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I would expect the following:

~~~
p = proc { |a| a * 2 }
l = lambda(&p)
puts l.lambda? # => true
l.call(1, 2) # => ArgumentError
~~~

But it does not, basically `l` there looks very much like a non-lambda proc (another test is that a return in `p` would cause `l.call` to raise LocalJumpError)

~~~
~~~



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