From: Bakul Shah <bakul@iitbombay.org>
To: srb@acm.org
Cc: tuhs@tuhs.org
Subject: [TUHS] Re: GOTO etc
Date: Sun, 12 Mar 2023 13:06:55 -0700 [thread overview]
Message-ID: <8D38925D-428C-4346-876A-9689BD41F375@iitbombay.org> (raw)
In-Reply-To: <eac9d81f-5350-3094-9141-51456ec2c645@unixsh.com>
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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@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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next prev parent reply other threads:[~2023-03-12 20:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-12 18:23 [TUHS] " Steve
2023-03-12 20:06 ` Bakul Shah [this message]
2023-03-12 21:10 ` [TUHS] " Paul Winalski
2023-03-16 20:35 ` Steve Bourne
2023-03-19 16:53 Bakul Shah
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