# Probability space valued functions

I am trying to define a FiniteProbabilitySpace whose probabilities depend on a value x:

**var('x')
S=[-1,0,1]
P={}
P[1] = lambda x: x
P[-1] = lambda x: x
P[0] = lambda x: 1.-2*x
Sp = DiscreteProbabilitySpace(S,P)**

Then if I say **Sp.entropy()**, I get the result:

**TypeError: bad operand type for unary -: 'function'**

which seems logic, I did not determine x. But if I say **Sp(0).entropy()**, I get:

**TypeError: Unable to convert x (='<function<lambda>at0xa65d2a8>') to real number.**

I do not understand this. Is it possible to do what I want?

Thank you very much!