Constant symbols

I'm working right now in the implementation of constant symbols. This is how constants are declared in Freya:

MathHelper = class
public
    const Pi: Double := 3.141592653589;
    const E = 2.718281828459;
end;

Constant can be declared inside a method implementation too:

method TrySave;
const
    MAX_ATTEMPTS = 3;
begin
    // ...
end;

Local constants are easy to implement, since they only exist at compile time, and member constants don't use them in their own definitions. On the other hand, member constants require a careful implementation. The expression in a constant declaration may contain references to other constants, as long as these references don't cause circular dependences. This is a simple example:

Trigonometry = static class
public
    const PiOver2 = MathHelper.Pi / 2.0;
    // ...
end;

MathHelper = class
public
    const Pi: Double := 3.141592653589;
    // ...
end;

I think I'll handle constant definitions right before performing "body resolution" on the Abstract Syntax Tree. Probably, I'll gather all constants from the compiling project in a single list, to execute a topological sort on this list. I have a vague idea about a brute force algorithm for topological sort, but I'm afraid I'll have to check my copy of The Art of Computer Programming for a better approach.