| ▲ | adrian_b 4 hours ago | |
Following the recommendations of Knuth, the language Mesa, which was implemented at Xerox during the seventies, and which was a source of inspiration for various later languages, including Modula, Ada and Python, included a form of "restricted GOTO" which is the most useful kind of GOTO in my opinion. The Mesa restricted GOTO allowed jumping forwards, but not backwards, and it allowed jumping towards an outer block, but not towards an inner block. These 2 restrictions eliminate all the "harmful" features of the traditional GOTO, while retaining its advantages for handling exceptional conditions or for terminating multiple levels of nested program structures. The Common Lisp TAGBODY appears to be only partially restricted, by allowing backward jumps, so it does not prevent the kind of hard-to-understand program structures for which GOTO was criticized. GOTOs in random directions may be used to implement state machines, but such state machines can still be implemented in a language with restricted GOTO by not using GOTO, but by using mutually recursive procedures, if tail-call optimization is guaranteed. | ||
| ▲ | taeric 3 hours ago | parent [-] | |
I'm not clear that jumping backwards is that tough to reason with. Notably, Knuth's algorithms do that quite commonly, right? I do think they need to be somewhat constrained to not jump to places that need new things initialized. Which, it is truly mind blowing to know folks used to just jump straight into other functions. Mid function. Because why not. | ||