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std::cout << a(_y is 5, _z is 10) << std::endl;

I do think the idea of assigning inputs at the call site is important which is what you've done. It would be nice to use the named parameter library here if possible to get rid of the leading underscores.

class ArgTable

I think this is not needed if you can use the named parameter library.

class Equation

Should be templated I don't know what this offers over boost bind and function. I use these to do a lot of this type of stuff. As long as the number of parameters are low, its easy to understand and you get some currying for free. SomeFn f = bind(my_fn(),_1,_2); // its not too difficult to understand this as x,y // I'd really like to do double v = f(x=x,y=y); Sohail