I don't know if it can!
If you tie something, you are basically saying that you're implementing the interface for a built-in type, so that value can be stored in any so-typed variable.
Code is written that uses an INTEGER (In Perl6, the all-cap is the class, and the lowercase is the machine primitive, right?). You pass in a value that is really the Perl6 equivilent of Perl 5's tie feature, whatever it is called (the normal isa/implements syntax should do it, I suppose).
If assigning a value to it really has bizzare side effects, that code doesn't know it. Neither can a compiler or other tool doing static analysis of the code.
That's a property of the run-time value, not the lexical variable that holds it.
In reply to Re^5: Perl Programming ToolsPerl and IDEs
by John M. Dlugosz