insert: value at: position
((position < 1) or: [ position > (current+1)])
ifTrue: [ self error: 'invalid index for insert:at:'].
(current = values size) ifTrue: [ self reallocate ].
(position to: current) reverseDo:
[:i | values at: i+1 put: (values at: i)].
current <- current + 1.
values at: position put: value