I want to define a distribution in my model of the form: P(x=10)=0.10, P(x=15)=0.20, P(x=20)=0.70

The WinBUGS FAQ says it is possible construct my own discrete uniform distribution as a categorical variable with a uniform prior and which can take on the necessary integer values. See the blockerht example in the first part of the manual.

I looked the example up, I think it is this one: "A hierarchical t-distribution with unknown degrees of freedom"

At the model specification they do something like:

Which does define a discrete uniform. But I don't know how to get to the form I need. Can anyone help me?