Instead of IF c x y, use
(IF c q.x q.y)
here delays evaluation
Later, the result of the IF will be one or the other of these functions
Apply it to a dummy argument to yield the real result
IF can take care of applying to the dummy argument if we want:
IF = cxy.((c x y) Q)
Q can be chosen arbitrarily, since it's thrown away
We'll take Q = i.i from now on