Function qip::builders::try_condition

pub fn try_condition<F, RS, OS>(
    b: &mut dyn UnitaryBuilder, 
    cr: Register, 
    rs: RS, 
    f: F
) -> Result<(Register, OS), CircuitError> where
    F: FnOnce(&mut dyn UnitaryBuilder, RS) -> Result<OS, CircuitError>, 

Condition a circuit defined by f using cr, better supports Result types.