longjmp to an earlier stage where you can "retract" the error or somehow wrap it in a chainable form (e.g. add a union to your result to signal whether it's a v

longjmp to an earlier stage where you can "retract" the error or somehow wrap it in a chainable form (e.g. add a union to your result to signal whether it's a value or error, or whatever) That's what exceptions are supposed to do. C doesn't have exceptions, so you use setjmp/longjmp.