how to parse linear equations

[Michael Chen]

Dear there,

The input I have is linear equation like:

2 * x + ( x - y ) = x + 1

And I would like to get at end

2 * x - y = 1

I studied the calculator example, and be able to build ast tree.
however  I have no way to reduce it. Please give me an example or
link. Thanks.
-- 
Best regards,
Michael Chen