Propagation of uncertainty

A simplified example to clarify
I have a set of points (x,y) and a linear model, whose parameters I can estimate with a fit y=ax+b in pymc

In this way I find the pdfs for a and b

Next, I want to use these parameters, in another function
y’=a+cx’+e^bx’
to see the predictions with respect to a different dataset
Is there an example that can guide me?