being or not being?

This question is about English style with regard to Java.

  The context is a tutorial that just said:

      The activation of an operation expression is called
      »evaluation«. It will activate the operation that is
      given by the expression.

  (So far only expressions of the form »m()« have been
  discussed.)

  Now the question how to write the next sentence:

  I assume that the following sentences are all correct.
  But which one is to prefer for a tutorial?

      For example, when the expression
      »java.lang.Thread.dumpStack()« is evaluated, the 
      operation »java.lang.Thread.dumpStack()« is activated.

      For example, when the expression
      »java.lang.Thread.dumpStack()« is being evaluated, the 
      operation »java.lang.Thread.dumpStack()« is being activated.

  (There also might be other possibilities, which seem more
  remote to me, such as:

      For example, when the expression
      »java.lang.Thread.dumpStack()« will be evaluated, the 
      operation »java.lang.Thread.dumpStack()« will be activated.

      For example, if the expression
      »java.lang.Thread.dumpStack()« would be evaluated, the 
      operation »java.lang.Thread.dumpStack()« would be activated.)

  Is there a difference in the meaning of the examples that is
  relevant when discussing evaluation of such expressions?

  I am especially interested in the question of when to use »being«.