consolidate constants for Add cases

[JustinBanzon]

Is your feature request related to a problem? Please describe.
I am implementing the Sine function and am noticing that Pi, Real, and EulerNumber are constants with different class types.

Describe the solution you'd like
I'd like there to be a way to consolidate Add<Constant,Expression> for constants like multiples of Pi or Euler's number.

Describe alternatives you've considered
One alternative I have considered so far is making cases for integrating each type of constant, which can become repetitive. An option to consolidate constant values that might be feasible to make a class that the Real, Pi, and EulerNumber classes build off of.

[matthew-mccall]

Hi, this a good point. Right now, I think a solution might be to modify RecursiveCast to match Pi and EulerNumber against Real. This would also mean implicitly casting Pi and EulerNumber to Real which means we lose the semantic meanings of those numbers. However, a long-term solution might be to create a templated case, and provided specialized cases to MatchCast covering your scenario.

[404Naz]

Another solution could involve modifying the inheritance tree of those values to inherit from a Constant class that inherits from leaf expression for all classes that have a GetValue() function. This could prevent having to modify RecursiveCast with new cases it we add any new constants in the future. However, I do not know if it is possible to add this capability due to the way abstract classes work.