Ok, I'll give it a try, but take it with a reserve.
It depends on amount of time you are willing to invest into the project. If you want it fast, you can use the regexp solution. The option with ignoring array elements would open a gray area of cheating where you could be easily caught. I'd rather report "I don't understand, please rephrase", then give an option that I can't handle more or less successfully.
But, if you want to be really noticed, there is a third option. It should be a free online English parser service somewhere out there. You can try to syntactically analyze human input sentence, pairing it with previous computer output. With drawn conclusions about input-output pair, I'd store it as a behavior pattern. On the next human input, I'd apply the learned behavior, and see what behavior could be concluded after the latest output, and again I'd store it to our artificial mind. After a while, we would have a decent behavior database, powered by comparing syntactic elements between inputs and outputs. For doing this, I'd have to find a decent ontology system where I'd store gathered knowledge. Probably I'd group it by verbs, enumerating possible subject/object/complement/whatever sets that may be used with the verb, which I'd use as a base for analyzing our input-output.
Now, this analysis could be done in a top-down manner, generalizing possible inputs-outputs towards functions where F(input) = output, but that would probably turn out to be a hard nut, so I'd probably go with neural networks, if the top-down approach fails. I think we should have some decent logic background for top-down approach, but this steep curve learning could be avoided in NN approach. Opposite to top-down approach, NN could be fed by given input, and trained to produce given output. After a month of feeding the baby with whatever data, some results should be seen. If not, we did something wrong, so we'd have to revise the whole algorithm. But be careful, it may turn out that the baby, when approaching adulthood, might be smarter than us, so then would be a fine time to think about some precaution measures like Asimov's laws, or something.
And then? Then I'd start to ask the baby real questions like: how can we improve our society, science, everyday life, and stuff like that. I wonder where would it end...
Sorry, I couldn't resist to giving the third option... Didn't I tell you about me giving awful advices?