Andrew wrote:It would require a lot of messy special-case code to handle explosive rules like that.
I'm not familiar with Golly's internals, but (naively) I'd think it would just take a single extra variable to keep track of the "background" state. Update it at every step using the transition X,X,X,X,X,Y (X being the current background, and Y the new one). And everywhere Golly assumes a region consists entirely of dead cells, it should instead assume those cells have the background state.
Andrew wrote:The real question is, would it be worth doing? Given that an explosive rule can usually (always?) be emulated by a non-explosive rule (possibly with extra states), there doesn't seem much point.
Yeah, agreed. Which is why I suggested showing an error message (when a transition like 0,0,0,0,0,!0 is found). But I understand if you don't want to add handling for this edge case.