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=EF=BB=BFThanks! Is this w= here unix setjmp/longjmp names come from? (I assume setmp in your message is= a typo?)

Algol68 Revised Report h= as this delightful example in section 5.4.4:

proc void m :=3D goto north berwick=

:-) If m is passed as an argu= ment to another function, calling m can return to within the parent f= unction of m but it may *not* be in the scope of the called function (= somewhat like unix setjmp/longjmp) though I don=E2=80=99t recall now if Algo= l68 allows passing such functions.

Could setjmp/lon= gjmp have been used to allow some register caching since register held value= s would be restored upon longjmp? But that can't be quite right since the sa= me values can be modified by code after the label. [No idea about the state o= f optimizations in those days]

On Mar 19, 2023, at 8:41 AM, Steve <srb@unixsh.com> wrote= :

=EF=BB= =BF =20 =20 =20 
After some digging - in the Algol68C compiler we used the names s=
etmp and longjmp for the code generation routines to implement non local got=
o.  So
as you say they were not part of the Algol68 language. =20

Steve

From: Bakul Shah <bakul@iitbombay.org>
Subject: [TUHS] Re: GOTO etc
To: srb@acm.org

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 le=
vel of a REPL or to jump to a known place after an error.


On Mar 12, 2023, at 11:24 AM, S=
teve <s=
rb@unixsh.com> wrote:

=EF=BB=BF Dennis added setjmp() and longjmp() so the shell could handle erro=
rs in a reasonable way.
There are two places where setjmp was used in the original shell (7th editio=
n) 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 invente=
d.  longjmp() was used in the "exitsh"
function that got called on the exit command, default trap routine and a fau=
lt with no trap set.

It was also used when executing a subshell to avoid a fork and exec.  In thi=
s 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 re=
covery and one to reset the execution environment
back to initial state.

Steve
=20
= --Apple-Mail-88710E4E-F9D7-49E9-801F-64385572E5FD--