Callback with errors?

[delaneyj]

Functions like StructFunc take a Group but don't return an error. I have conditions where iterating and creating the fields must error out. Right now i'm jumping through hoop to get that error. Since these callback functions are generated and I'm sure changing the function signature would cause havoc could another version be generated?

Something like

StructFuncErr(f func(*Group) error) (*Statement,error)