[Haskell-cafe] Find a point inside (x,y,z) -> Bool

Hello all, I hope this is not a too silly question. It goes like this: Suppose I have a shape defined as (x,y,z) -> Bool how can I find a Point inside this shape? Obviously I could iterate through all possible x,y and z, but this appears very expensive. There may be no point at all at x=0. With brute force iteration I would have no clue that the False I am receiving with (0,1,1) is caused by x=0 and I may nedlessly try all combinations of y and z without ever receiving a True. Are there any alternative ways of finding points inside a shape?