Negate a predicate Proc in Ruby

Question

I have a Proc, which is predicate.

Proc.new { |number| number.even? }

Is there a way to somehow create another Proc which have the opposite meaning? I can't change the "body" of the Proc, because the Proc will come as function parameter. So I want something like this:

not(Proc.new { |number| number.even? }
# which of course doesn't work :(

and I want it to do the same as

Proc.new { |number| number.odd? }

The idea is that I want a function similar to this:

def negate(proc)
  negated proc with meaning opposite of this of proc
end

Thank you very much in advance!

Answer 1

The following method returns the procedure opposite to the provided one.

def negate(procedure)
  Proc.new { |*args| !procedure.call(*args) }
end

or, using shorter notation:

def negate(procedure)
  proc { |*args| !procedure.call(*args) }
end

Answer 2

Does this help at all?

p = Proc.new { |number| number.even? }
p.call(1) #=> false
!p.call(1) #=> true