code: def WHEN(condition, adjuster)
        unless Validation.conditionable? condition
          raise TypeError, 'wrong object for condition'
        end
  
        unless Validation.adjustable? adjuster
          raise TypeError, 'wrong object for adjuster'
        end
  
        ->v{_valid?(condition, v) ? adjuster.call(v) : v}
      end
docs: Adjuster Builders
   Apply adjuster when passed condition.
   @param condition [Proc, Method, #===]
   @param adjuster [Proc, #to_proc]
   @return [lambda]