10 Mar
2023
10 Mar
'23
12:51 p.m.
From: Warner Losh
for breaking out of multiple levels of while/for
loops.
Yeah, multi-level 'breaks' were one of the things I really missed in C.
The other was BCPL's 'VALOF/RESULTIS'. Back before C compilers got good
enough to do inline substitutions of small procedures (making macros with
arguments less useful), it would have been nice to have, for macros that
wanted to return something. Instead, one had to stand on one's head and use a
'(cond ? ret1 : ret2 )' of some form.
Noel
10 Mar
10 Mar
3:16 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
Multilevel breaks are as bad as goto with regard to structure violation.
------ Original Message ------
From "Noel Chiappa" <jnc(a)mercury.lcs.mit.edu>
To tuhs(a)tuhs.org
Date 3/10/2023 6:51:45 AM
Subject [TUHS] Re: I can't drive 55: "GOTO considered harmful" 55th
anniversary
From: Warner
Losh
for breaking out of multiple levels of while/for
loops.
Yeah, multi-level 'breaks' were one of the things I really missed in C.
3:39 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
On Fri, Mar 10, 2023 at 9:16 AM Ronald Natalie <ron(a)ronnatalie.com> wrote:
Multilevel breaks are as bad as goto with regard to structure violation.
No more so than `return` statements in arbitrary places, which nobody
worries about any more.
5:30 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
ron(a)ronnatalie.com wrote:
Multilevel breaks are as bad as goto with regard to
structure violation.
Back when I was in compilers (so long ago, that it was the DEC PDP-10
FORTRAN compiler(*)) my recall is that break/continue never generated
irreducible flow graphs, as goto can:
https://en.wikipedia.org/wiki/Control-flow_graph#Reducibility
I still remember the days when you could find C code written by PASCAL
programmers, littered with condition variables on loops, and if
statements to not execute the tail of the loop body if the loop
condition was false.
(*) The FORTRAN compiler was written in BLISS-10, which had labeled
statements, and a "leave <label>" construct which was only legal
inside the labeled statement:
http://www.bitsavers.org/pdf/dec/pdp10/TOPS10/DEC-10-LBRMA-A-D_BLISS-10_Pro…
6:50 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
Phil Budne wrote in
<202303101630.32AGU2OD008070(a)ultimate.com>:
|ron(a)ronnatalie.com wrote:
|> Multilevel breaks are as bad as goto with regard to structure violation.
|
|Back when I was in compilers (so long ago, that it was the DEC PDP-10
|FORTRAN compiler(*)) my recall is that break/continue never generated
|irreducible flow graphs, as goto can:
|
|https://en.wikipedia.org/wiki/Control-flow_graph#Reducibility
|
|I still remember the days when you could find C code written by PASCAL
|programmers,[.]
|littered[.]
I love this.
|with condition variables on loops, and if
|statements to not execute the tail of the loop body if the loop
|condition was false.
|
|(*) The FORTRAN compiler was written in BLISS-10, which had labeled
|statements, and a "leave <label>" construct which was only legal
|inside the labeled statement:
|
|http://www.bitsavers.org/pdf/dec/pdp10/TOPS10/DEC-10-LBRMA-A-D_BLISS-10_\
|Programmers_Manual_Ver_4_Feb74.pdf#page=42
--End of <202303101630.32AGU2OD008070(a)ultimate.com>
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)
6:57 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
Phil Budne wrote in
<202303101630.32AGU2OD008070(a)ultimate.com>:
|ron(a)ronnatalie.com wrote:
|
|I still remember the days when you could find C code written by PASCAL
|programmers,[.]
Someone once observed that a skilled FORTRAN programmer could write
FORTRAN in any programming language.
-Paul W.
7:12 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
On Mar 10, 2023, at 12:57 PM, Paul Winalski
<paul.winalski(a)gmail.com> wrote:
Once taught a programming languages class at Stanford, with assignments in Pascal, APL,
LISP, and SNOBOL. The SNOBOL was to solve a crossword by pattern matching, given the grid
and the solution words.
One kid had by far the fastest solution, in SNOBOL, but if you held up the listing at
arm’s length you would swear it was FORTRAN.
I write my FORTRAN code in C these days.
-L
Phil Budne wrote in
<202303101630.32AGU2OD008070(a)ultimate.com>:
|ron(a)ronnatalie.com wrote:
|
|I still remember the days when you could find C code written by PASCAL
|programmers,[.]
Someone once observed that a skilled FORTRAN programmer could write
FORTRAN in any programming language.
-Paul W. 
6:28 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
On Fri, Mar 10, 2023 at 9:16 AM Ronald Natalie <ron(a)ronnatalie.com> wrote:
Multilevel breaks are as bad as goto with regard to
structure violation.
Amen. My memory of the argument at the time was one of pick your poison.
Each language has trade-offs and it depends on what you value. C was
considered "dirty" by many CS types in the day compared to languages like
Pascal, Simula67, Algol-X.
I've always said the key was what was left out of the language, not what
was put in. Dennis offers a few important pieces of wisdom here:
- "When I read commentary about suggestions for where C should go, I
often think back and give thanks that it wasn't developed under the advice
of a worldwide crowd."
- "A language that doesn't have everything is actually easier to program
in than some that do."
- "C is quirky, flawed, and an enormous success."
Arnold's observation about trying to be small is reasonable,
although contemporaries like BLISS did have support. So the comparison
should really be to BCPL, PL/360, BLISS, *et al*. for features/size
[although Wulf cheated, the BLISS-11 compiler was not self-hosting and
needed a PDP-10 to run it].
ᐧ
6:54 p.m.
New subject: I can't drive 55: "GOTO considered harmful" 55th anniversary
On 3/10/23, Clem Cole <clemc(a)ccc.com> wrote:
Arnold's observation about trying to be small is reasonable,
although contemporaries like BLISS did have support. So the comparison
should really be to BCPL, PL/360, BLISS, *et al*. for features/size
[although Wulf cheated, the BLISS-11 compiler was not self-hosting and
needed a PDP-10 to run it].
For what it's worth, BLISS does not have a GOTO expression (BLISS
doesn't have statements per se--everything is an expression and can be
used as a value).
Wulf was studying code optimization. His BLISS-11 compiler, and its
successor at DEC, BLISS-16, implemented many advanced (for the day)
optimizations. In the programming environments at CMU and DEC it was
easier to suffer the mild inconvenience of cross-compilation than to
try to shoehorn the compiler into a 16-bit address space.
It certainly would be possible to implement a native BLISS compiler
for the PDP-11, but you'd have to sacrifice either some of the
optimizations or take a big hit in compilation speed.
-Paul W.
620
days inactive
620
days old
8 comments
8 participants
participants (8)
-
Clem Cole -
jnc＠mercury.lcs.mit.edu -
John Cowan -
Lawrence Stewart -
Paul Winalski -
Phil Budne -
Ronald Natalie -
Steffen Nurpmeso