calcELIZAr can apply the four basic arithmetic operations to two integer operands. It understands ordinary questions written in English.
It is clear that the engine cannot cover all possible formulations. On the other hand, to keep the code simple, it will accept some invalid questions or creates some wrong results as well. Please keep in mind that English is not calcELIZAs' first language. ;)
ELIZA was first implemented by Joseph Weizenbaum in 1966.