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)
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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