An invocation pluck P [x1,...,xk,...,xn] returns a pair
(xk,[x1,...,xk-1,xk+1,...xn]), where xk has been lifted out of the
list without disturbing the relative positions of the other elements. For
this to happen, P xk must hold, and P xi must not have held for
x1,...,xk-1.
FAILURE
If the input list is empty. Also fails if P holds of no member of the
list. Also fails if an application of P fails.
EXAMPLE
- val (x,rst) = pluck (fn x => x mod 2 = 0) [1,2,3];
> val x = 2 : int
val rst = [1, 3] : int list