Spawn object at middle of each layer boundaries

I want do spawn an object in these positions:

y = 0; x = WindowWidth/0 (Middle Top)

y = WindowHeight/2; x = 0 (Middle Left)

y = WindowHeight/2; x = WindowWidth (Middle Bottom)

y = WindowHeight; x = WindowWidth/0 (Middle Right)

Now I'm doing this:

Set Position at x = choose(WindowWidth/2,choose(0,WindowWidth)); y = choose(choose(0,WindowHeight),WindowHeight/2)

The problem is that this arrangment includes also 0,0 and WindowHeight,WindowWidth (Top Left and Bottom Right corners).

How can I achieve what I want? Does an IF condition exists somewhere for actions?

It also spawn at the center of the stage (clarification to give the thread another chance.. :-P)

RandomTRBL.capx

Wow, never thought about it! Thanks, really much appreciated