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[107.215.223.229]) by smtp.gmail.com with ESMTPSA id y26-20020a37f61a000000b007436d0c60ecsm3958092qkj.65.2023.03.12.13.07.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 12 Mar 2023 13:07:06 -0700 (PDT) Content-Type: multipart/alternative; boundary=Apple-Mail-D3180B36-1AE9-4AEA-865F-A50F91267A53 Content-Transfer-Encoding: 7bit From: Bakul Shah Mime-Version: 1.0 (1.0) Date: Sun, 12 Mar 2023 13:06:55 -0700 Message-Id: <8D38925D-428C-4346-876A-9689BD41F375@iitbombay.org> References: In-Reply-To: To: srb@acm.org X-Mailer: iPad Mail (20D67) Message-ID-Hash: 3JOTTPDOP4Q7HE2HUGH6JCHLJN25YYV4 X-Message-ID-Hash: 3JOTTPDOP4Q7HE2HUGH6JCHLJN25YYV4 X-MailFrom: bakul@iitbombay.org X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: tuhs@tuhs.org X-Mailman-Version: 3.3.6b1 Precedence: list Subject: [TUHS] Re: GOTO etc List-Id: The Unix Heritage Society mailing list Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: --Apple-Mail-D3180B36-1AE9-4AEA-865F-A50F91267A53 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Perhaps you=E2=80=99re talking about non-local GOTOs in Algol68, where you c= an jump from a nested procedure to a label in a lexically enclosing procedur= e. 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 o= f a REPL or to jump to a known place after an error. > On Mar 12, 2023, at 11:24 AM, Steve wrote: >=20 > =EF=BB=BF Dennis added setjmp() and longjmp() so the shell could handle er= rors in a reasonable way. > There are two places where setjmp was used in the original shell (7th edit= ion) code as I recall. Both at the top level > in main.c. >=20 > The idea came from Algol68 but I do not know where it was originally inven= ted. longjmp() was used in the "exitsh" > function that got called on the exit command, default trap routine and a f= ault with no trap set. >=20 > It was also used when executing a subshell to avoid a fork and exec. In t= his case the setjmp() was at top level > in the initial sh setup. >=20 > Hope this makes sense. But these were two different uses. One for error r= ecovery and one to reset the execution environment > back to initial state. >=20 > Steve --Apple-Mail-D3180B36-1AE9-4AEA-865F-A50F91267A53 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Per= haps you=E2=80=99re talking about non-local GOTOs in Algol68, where y= ou can jump from a nested procedure to a label in a lexically enclosi= ng 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, S= teve <srb@unixsh.com> wrote:

=EF=BB=BF =20 =20 =20 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.  O= ne for error recovery and one to reset the execution environment
back to initial state.

Steve
 =20
= --Apple-Mail-D3180B36-1AE9-4AEA-865F-A50F91267A53--