12 Mar
2023
12 Mar
'23
7:23 p.m.
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
12 Mar
12 Mar
9:06 p.m.
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(a)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
16 Mar
16 Mar
9:35 p.m.
Hi Bakul, yes non local GOTOs. In the Algol68C compiler we wrote we used the names setmp
and longjmp
for the code generation routines to implement non local goto. So as you say they were not
partof
the Algol68 language.
Steve
On 3/12/23 5:10 PM, Paul Winalski wrote:
On 3/12/23, Bakul Shah<bakul(a)iitbombay.org>
wrote:
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.
So does PL/I.
-Paul W.
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3 comments
4 participants
participants (4)
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Steve Bourne