Quantum symbol expressions won't work with addition

[Doomsk]

It is possible to evaluate

a = parameter("a")
b = parameter("b")
print(a + b)

however it raises a generic error when doing it with quantum operators

X(1) + Z(1)

It may be helpful if an appropriate error is raised stating that this is not a valid expression.

[kaosmicadei]

The expression X(1) + Z(1) is valid and can be assigned to a variable.

h = 0.7071 * (X(1) + Z(1))
U = exp(-0.5j * h)

However, X(1) + Z(1) by itself cannot be compiled since there isn't an "addition gate". It needs to be replaced by an equivalent gate first.

replace(U, {0.7071 * (X(1) + Z(1)): H(1)})

Currently, this substitution needs to be performed manually. Future steps of the development would include some automatic analysis of the expressions.