Categorical Distribution in RooFit

Hello!

I’m new to RooFit and am stuck at something that seems pretty trivial: I’m trying to treat categorical distribution in RooFit but I have no idea to treat parameters’ constraints.

Would you like to help me solve this problem?

==The model==
Parameters: a, b, c.
Constraints:
a+b+c=1
0 <= a <= 1
0 <= b <= 1
0 <= c <= 1

PDF:
P(X)=
a if X=A,
b if X=B,
c if X=C.
(X takes only A,B or C.)

I also need to integrate this pdf by a, b and c. So I hope a, b, c are RooRealVar.

Thanks,
Jun-ya Norimatsu