[TUHS] GOTO etc.

[Steve]

After some digging - in the Algol68C compiler we used the names setmp and longjmp for the code 
generation routines to implement non local goto.  So as you say they were not part of the Algol68 
language. Steve
From: Bakul Shah<bakul at iitbombay.org>
Subject: [TUHS] Re: GOTO etc
To:srb at acm.org

Perhaps you’re talking about non-local GOTOs in Algol68, where you can jump from a nested procedure to a label in a lexically enclosing procedure. Pascal has this too. C has no nested procedures but its setjmp/longjmp is much more powerful (& dangerous). Though both can be used to the top level of a REPL or to jump to a known place after an error.

> On Mar 12, 2023, at 11:24 AM, Steve<srb at unixsh.com>  wrote:
>
>  Dennis added setjmp() and longjmp() so the shell could handle errors in a reasonable way.
> There are two places where setjmp was used in the original shell (7th edition) code as I recall.  Both at the top level
> in main.c.
>
> The idea came from Algol68 but I do not know where it was originally invented.  longjmp() was used in the "exitsh"
> function that got called on the exit command, default trap routine and a fault with no trap set.
>
> It was also used when executing a subshell to avoid a fork and exec.  In this case the setjmp() was at top level
> in the initial sh setup.
>
> Hope this makes sense.  But these were two different uses.  One for error recovery and one to reset the execution environment
> back to initial state.
>
> Steve
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