Proposal/Question: Type assertions on the entire error stack

Originally, checking if a error matches a given interface, you would simply m, ok := err.(myInterface). With pkg/errors, it's now m, ok := errors.Cause(err).(myInterface) (Basing this off of the writing here: http://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully)

However, this falls apart if your error stack has myInterface in the middle, since errors.Cause(err).(myInterface) only checks the bottom of the stack:

err := errors.New("Sample error")
// because myCodedError is in the middle of a stack, we have no way
// of getting at Code without writing a custom function that is a near 
// clone of errors.Cause()
err = &myCodedError{code: 404, err: err}
err = Wrap(err, "Wrapping 1")
err = Wrap(err, "Wrapping 2")
err = Wrap(err, "Wrapping 3")

Question: What is the best way to handle this? Custom functions for each of your interfaces which may get paired with a causer. A generalized function added to pkg/errors?

I've thrown up some code here which shows the varying cases and solutions https://play.golang.org/p/E8eJeWbOuV