Calling functions from plain text descriptions

I have an app which has common maths functions behind the scenes:

• add(x, y)
• multiply(x, y)
• square(x)

The interface is a simple google- style text field. I want the user to be able to enter a plain text description -

• '2*3'
• '2 times 3'
• 'multiply 2 and 3'
• 'take the product of 2 and 3'

and get a answer mathematical answer

Question is, how should I map the text descriptions to the functions ? I'm guessing I need to

• tokenise the text
• identify key tokens (function names, arguments)
• try and map token combinations to function signatures

However I'm guessing this is already a 'solved problem' in the machine learning space. Should I be using Natural Language Processing ? Plain text search ? Something else ?

All ideas gratefully received, plus implementation suggestions [I'm using Python/AppEngine; I know about NLTK and Whoosh]

[PS I understand Go开发者_JAVA技巧ogle does this already, at least for the first two queries on the list. I'm guessing they also go it statistically, having a very large amount of search data. I don't have a large amount of data available, so will need an alternative approach].

After you tokenise the text, you need parsing to get a syntax tree of your natural language phrase. Once you have this, you can map the parse tree to a mathematical expression, and then evaluate the expression. I do not think this is a solved problem. I would start with several templates, say the first two, and experiment. The larger the domain of possible descriptions, the harder the task is.

I would recommend some tool for provide grammar/patterns on text like SimpleParse for python http://www.ibm.com/developerworks/linux/library/l-simple.html. As java programmer I would prefer GATE or graph-expression.