position(obj, xs, @key start = 0, test = is_eq)
Compare each element in the list xs to obj using the predicate test.
The comparison begins at the index specified by start.
Return the index of obj in the list xs.
Return false if obj is not found in the list.
position(10, [1, 2, 10, 3])
// 2
position("hi", [1, 2, "hi", 3])
// false
position("hi", [1, 2, "hi", 3], test = is_equal)
// 2
position("hi", [1, 2, "hi", 3], test = is_equal, start = 3)
// false
position("hi", [1, 2, "hi", 3], test = is_equal, start = 2)
// 2