[TUHS] The 'usage: ...' message. (Was: On Bloat...)

[TUHS] The 'usage: ...' message. (Was: On Bloat...)

[Douglas McIlroy]

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> was ‘usage: ...’ adopted from an earlier system?

"Usage" was one of those lovely ideas, one exposure to which flips its
status from unknown to eternal truth. I am sure my first exposure was on
Unix, but I don't remember when. Perhaps because it radically departs from
Ken's "?" in qed/ed, I have subconsciously attributed it to Dennis.

The genius of "usage" and "?" is that they don't attempt to tell one what's
wrong. Most diagnostics cite a rule or hidden limit that's been violated or
describe the mistake (e.g. "missing semicolon") , sometimes raising more
questions than they answer.

Another non-descriptive style of error message that I admired was that of
Berkeley Pascal's syntax diagnostics. When the LR parser could not proceed,
it reported where, and automatically provided a sample token that would
allow the parsing to progress. I found this uniform convention to be at
least as informative as distinct hand-crafted messages, which almost by
definition can't foresee every contingency. Alas, this elegant scheme seems
not to have inspired imitators.

Doug

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Paul Winalski]

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On Sun, May 19, 2024 at 10:03 AM Douglas McIlroy <
douglas.mcilroy@dartmouth.edu> wrote:

>
> Another non-descriptive style of error message that I admired was that of
> Berkeley Pascal's syntax diagnostics. When the LR parser could not proceed,
> it reported where, and automatically provided a sample token that would
> allow the parsing to progress. I found this uniform convention to be at
> least as informative as distinct hand-crafted messages, which almost by
> definition can't foresee every contingency. Alas, this elegant scheme seems
> not to have inspired imitators.
>
> The hazard with this approach is that the suggested syntactic correction
might simply lead the user farther into the weeds.  It depends on how far
the parse has gone off the rails before a grammatical error is found.
Pascal and BASIC (at least the original Dartmouth BASIC) have simple,
well-behaved grammars and the suggested syntactic correction is likely to
be correct.  It doesn't work as well for more syntactically complicated
languages such as C (consider an error resulting from use of == instead of
=) or PL/I.  And it's nigh on impossible for languages with ill-behaved
grammars such as Fortran and COBOL (among other grammatical evils, Fortran
has context-sensitive lexiing).

Commercial compiler writers avoid this techniq

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Paul Winalski]

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Ack!  I finger-fumbled and accidentally sent this message incomplete.
Here's the complete version.  Sorry about that, Chief!

On Sun, May 19, 2024 at 12:18 PM Paul Winalski <paul.winalski@gmail.com>
wrote:

> On Sun, May 19, 2024 at 10:03 AM Douglas McIlroy <
> douglas.mcilroy@dartmouth.edu> wrote:
>
>>
>> Another non-descriptive style of error message that I admired was that of
>> Berkeley Pascal's syntax diagnostics. When the LR parser could not proceed,
>> it reported where, and automatically provided a sample token that would
>> allow the parsing to progress. I found this uniform convention to be at
>> least as informative as distinct hand-crafted messages, which almost by
>> definition can't foresee every contingency. Alas, this elegant scheme seems
>> not to have inspired imitators.
>>
>> The hazard with this approach is that the suggested syntactic correction
> might simply lead the user farther into the weeds.  It depends on how far
> the parse has gone off the rails before a grammatical error is found.
> Pascal and BASIC (at least the original Dartmouth BASIC) have simple,
> well-behaved grammars and the suggested syntactic correction is likely to
> be correct.  It doesn't work as well for more syntactically complicated
> languages such as C (consider an error resulting from use of == instead of
> =) or PL/I.  And it's nigh on impossible for languages with ill-behaved
> grammars such as Fortran and COBOL (among other grammatical evils, Fortran
> has context-sensitive lexiing).
>
> Commercial compiler writers avoid this techniq
>

Commercial compiler writers avoid this technique because it turns into an
error report generator.  The potential user benefit is outweighed by all of
the "your compiler suggested X as a correction when the problem was Y"
that need to be answered.

-Paul W.

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[TUHS] Re: The 'usage: ...' message.

[Ralph Corderoy]

Hi Doug,

> Perhaps because it radically departs from Ken's "?" in qed/ed

That spread elsewhere.  When PDP-7 Unix's cp.s is given an odd number of
arguments, leaving the last unpaired, it prints the argument followed by
‘ ?’.  https://www.tuhs.org/cgi-bin/utree.pl?file=PDP7-Unix/cmd/cp.s

    mes:
       040000;077012		

    unbal:				
       lac name2			
       tad d4			
       dac 1f
       lac d1
       sys write; 1: 0; 4
       lac d1
       sys write; mes; 2
       sys exit

-- 
Cheers, Ralph.

[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Dave Horsfall]

On Sun, 19 May 2024, Douglas McIlroy wrote:

> Another non-descriptive style of error message that I admired was that 
> of Berkeley Pascal's syntax diagnostics. When the LR parser could not 
> proceed, it reported where, and automatically provided a sample token 
> that would allow the parsing to progress. I found this uniform 
> convention to be at least as informative as distinct hand-crafted 
> messages, which almost by definition can't foresee every contingency. 
> Alas, this elegant scheme seems not to have inspired imitators.

I did something like that for our compiler-writing assignment.  An 
ALGOL-like language (I think I used ALGOLW) it would detect when a 
semicolon was missing, and insert it (with a warning).  As a test case, it 
successfully compiled a program with no semicolons at all...

-- Dave

[TUHS] The 'usage: ...' message. (Was: On Bloat...)

[Douglas McIlroy]

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>> Another non-descriptive style of error message that I admired was that
>> of Berkeley Pascal's syntax diagnostics. When the LR parser could not
>> proceed, it reported where, and automatically provided a sample token
>> that would allow the parsing to progress. I found this uniform
>> convention to be at least as informative as distinct hand-crafted
>> messages, which almost by definition can't foresee every contingency.
>> Alas, this elegant scheme seems not to have inspired imitators.

> The hazard with this approach is that the suggested syntactic correction
> might simply lead the user farther into the weeds

I don't think there's enough experience to justify this claim. Before I
experienced the Berkeley compiler, I would have thought such bad outcomes
were inevitable in any language. Although the compilers' suggestions often
bore little or no relationship to the real correction,  I always found them
informative. In particular, the utterly consistent style assured there was
never an issue of ambiguity or of technical jargon.

The compiler taught me Pascal in an evening. I had scanned the Pascal
Report a couple of years before but had never written a Pascal program.
With no manual at hand, I looked at one program to find out what
mumbo-jumbo had to come first and how to print integers, then wrote the
rest by trial and error. Within a couple of hours  I had a working program
good enough to pass muster in an ACM journal.

An example arose that one might think would lead "into the weeds". The
parser balked before 'or' in a compound Boolean expression like  'a=b and
c=d or x=y'. It couldn't suggest a right paren because no left paren had
been seen. Whatever suggestion it did make (perhaps 'then') was enough to
lead me to insert a remote left paren and teach me that parens are required
around Boolean-valued subexpressions. (I will agree that this lesson might
be less clear to a programming novice, but so might be many conventional
diagnostics, e.g. "no effect".)

Doug

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Rob Pike]

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The Cornell PL/I compiler, PL/C, ran on the IBM 360 so of course used batch
input. It tried automatically to keep things running after a parsing error
by inserting some token - semicolon, parenthesis, whatever seemed best -
and continuing to parse, in order to maximize the amount of input that
could be parsed before giving up. At least, that's what I took the
motivation to be. It rarely succeeded in fixing the actual problem, despite
PL/I being plastered with semicolons, but it did tend to ferret out more
errors per run. I found the tactic helpful.

-rob

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[arnold]

Rob Pike <robpike@gmail.com> wrote:

> The Cornell PL/I compiler, PL/C, ran on the IBM 360 so of course used batch
> input. It tried automatically to keep things running after a parsing error
> by inserting some token - semicolon, parenthesis, whatever seemed best -
> and continuing to parse, in order to maximize the amount of input that
> could be parsed before giving up. At least, that's what I took the
> motivation to be. It rarely succeeded in fixing the actual problem, despite
> PL/I being plastered with semicolons, but it did tend to ferret out more
> errors per run. I found the tactic helpful.
>
> -rob

Gawk used to do this, until people started fuzzing it, causing cascading
errors and eventually core dumps. Now the first syntax error is fatal.
It got to the point where I added this text to the manual:

	In recent years, people have been running "fuzzers" to generate
	invalid awk programs in order to find and report (so-called)
	bugs in gawk.

	In general, such reports are not of much practical use. The
	programs they create are not realistic and the bugs found are
	generally from some kind of memory corruption that is fatal
	anyway.

	So, if you want to run a fuzzer against gawk and report the
	results, you may do so, but be aware that such reports don’t
	carry the same weight as reports of real bugs do.

(Yeah, I've just changed the subject, feel free to stay on topic. :-)

Arnold

[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Warner Losh]

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On Sun, May 19, 2024, 9:19 PM <arnold@skeeve.com> wrote:

> Rob Pike <robpike@gmail.com> wrote:
>
> > The Cornell PL/I compiler, PL/C, ran on the IBM 360 so of course used
> batch
> > input. It tried automatically to keep things running after a parsing
> error
> > by inserting some token - semicolon, parenthesis, whatever seemed best -
> > and continuing to parse, in order to maximize the amount of input that
> > could be parsed before giving up. At least, that's what I took the
> > motivation to be. It rarely succeeded in fixing the actual problem,
> despite
> > PL/I being plastered with semicolons, but it did tend to ferret out more
> > errors per run. I found the tactic helpful.
> >
> > -rob
>
> Gawk used to do this, until people started fuzzing it, causing cascading
> errors and eventually core dumps. Now the first syntax error is fatal.
> It got to the point where I added this text to the manual:
>
>         In recent years, people have been running "fuzzers" to generate
>         invalid awk programs in order to find and report (so-called)
>         bugs in gawk.
>
>         In general, such reports are not of much practical use. The
>         programs they create are not realistic and the bugs found are
>         generally from some kind of memory corruption that is fatal
>         anyway.
>
>         So, if you want to run a fuzzer against gawk and report the
>         results, you may do so, but be aware that such reports don’t
>         carry the same weight as reports of real bugs do.
>
> (Yeah, I've just changed the subject, feel free to stay on topic. :-)
>


Awk bailing out near line 1.

Warner

> Arnold
>

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[arnold]

Warner Losh <imp@bsdimp.com> wrote:

> > (Yeah, I've just changed the subject, feel free to stay on topic. :-)
>
> Awk bailing out near line 1.

	$ gawk --nostalgia
	awk: bailing out near line 1
	Aborted (core dumped)

A very long time Easter Egg... :-)

Arnold

[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Bakul Shah via TUHS]

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I remember helping newbie students at USC who were very confused that even though they made the changes "PL/C USES", their program didn't work! 

> On May 19, 2024, at 5:58 PM, Rob Pike <robpike@gmail.com> wrote:
> 
> The Cornell PL/I compiler, PL/C, ran on the IBM 360 so of course used batch input. It tried automatically to keep things running after a parsing error by inserting some token - semicolon, parenthesis, whatever seemed best - and continuing to parse, in order to maximize the amount of input that could be parsed before giving up. At least, that's what I took the motivation to be. It rarely succeeded in fixing the actual problem, despite PL/I being plastered with semicolons, but it did tend to ferret out more errors per run. I found the tactic helpful.
> 
> -rob
> 


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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Clem Cole]

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I was going to keep silent on this one until I realized I disagree with
both Doug and Rob here (always a little dangerous). But because of personal
experience, I have a pretty strong opinion is not really a win.  Note that I
cribbed this email response from an answer I wrote on Quora to the
question:

*When you are programming and commit a minor error, such as forgetting a
semicolon, the compiler throws an error and makes you fix it for yourself.
Why doesn’t it just fix it by itself and notify you of the fix instead?*


FWIW: The first version of the idea that I now about was DWIM - *Do What I
Mean* feature from BBN’s LISP (that eventually made it into InterLISP). As
the Wikipedia page describes DWIM became known as "Damn Warren's Infernal
Machine" [more details in the DWIM section of the jargon file].  As Doug
points out, the original Pascal implementation for Unix, pix(1), also
supported this idea of fixing your code for you, and as Rob points out, UCB’s
pix(1) took the idea of trying to keep going and make the compile work from
the earlier Cornell PL/C compiler for the IBM 360[1], which to quote
Wikipedia:

“The PL/C compiler had the unusual capability of never failing to compile
> any program, through the use of extensive automatic correction of many
> syntax errors and by converting any remaining syntax errors to output
> statements.”


The problem is that people can be lazy, and instead of using " DWIM" as a
tool to speed up their development and fix their own errors, they just
ignore the errors. In fact, when we were teaching the “Intro to CS” course
at UCB in the early 1980s; we actually had students turn in programs that
had syntax errors in them because pix(1) had corrected their code -- instead
of the student fixing his/her code before handing the program into the TA
(and then they would complain when they got “marked down” on the assignment
— sigh).

IMO: All in all, the experiment failed because many (??most??) people
really don’t work that way. Putting a feature like this in an IDE or even
an editor like emacs might be reasonable since the sources would be
modified, but it means you need to like using an IDE. I also ask --> what
happens when the computer’s (IDE) guess is different from the programmer's
real intent, and since it was ‘fixed’ behind the curtain, you don’t notice
it?

Some other people have suggested that DWIM isn’t a little like spelling
‘auto-correct’ or tools like ‘Grammarly.’ The truth is, I have a love/hate
relationship with auto-correct, particularly on my mobile devices. I'm
dyslexic, so tools like this can be helpful to me sometimes, but I spend a
great deal of my time fighting these types of tools because they are so
often wrong, particularly with a small screen/keyboard, that it is just
“not fun.”

This brings me back to my experience. IMO, auto-correct for programming is
like DWIM all over again, and the cure causes more problems than it solves.

Clem

[1] I should add that after Cornell’s PL/C compiler was introduced, IBM
eventually added a similar feature to its own PL/1, although it was not
nearly as extensive as the Cornell solution. I’m sure you can find people
who liked it, but in both cases, I personally never found it that useful.

>
ᐧ

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Greg A. Woods]

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At Mon, 20 May 2024 10:23:56 -0400, Clem Cole <clemc@ccc.com> wrote:
Subject: [TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)
>
> This brings me back to my experience. IMO, auto-correct for programming is
> like DWIM all over again, and the cure causes more problems than it solves.

We're deep down that rabbit hole this time with LLM/GPT systems
generating large swathes of code that I believe all too often gets into
production without any human programmer fully vetting its fitness for
purpose, or perhaps even understanding it.

--
					Greg A. Woods <gwoods@acm.org>

Kelowna, BC     +1 250 762-7675           RoboHack <woods@robohack.ca>
Planix, Inc. <woods@planix.com>     Avoncote Farms <woods@avoncote.ca>

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[John Levine]

It appears that Clem Cole <clemc@ccc.com> said:
>“The PL/C compiler had the unusual capability of never failing to compile
>> any program, through the use of extensive automatic correction of many
>> syntax errors and by converting any remaining syntax errors to output
>> statements.”
>
>The problem is that people can be lazy, and instead of using " DWIM" as a
>tool to speed up their development and fix their own errors, they just
>ignore the errors. ...

PL/C was a long time ago in the early 1970s. People used it on batch
systems whre you handed in your cards at the window, waited a while,
and later got your printout back. Or at advanced places, you could
run the cards through the reader yourself, then wait until the batch
ran.

In that environment, the benefit from possibly guessing an error
correction right meant fewer trips to the card reader. In my youth I
did a fair amount of programming that way in WATFOR/WATFIV and Algol W
where we really tried to get the programs right since we wanted to
finish up and go home.

When I was using interactive systems where you could fix one bug and
try again, over and over, it seemed like cheating.

R's,
John

[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[John Cowan]

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On Mon, May 20, 2024 at 4:11 PM John Levine <johnl@taugh.com> wrote:

It appears that Clem Cole <clemc@ccc.com> said:
> >“The PL/C compiler had the unusual capability of never failing to compile
> >> any program, through the use of extensive automatic correction of many
> >> syntax errors and by converting any remaining syntax errors to output
> >> statements.”
> PL/C was a long time ago in the early 1970s. People used it on batch
> systems whre you handed in your cards at the window, waited a while,
> and later got your printout back. Or at advanced places, you could
> run the cards through the reader yourself, then wait until the batch
> ran.


PL/C was a 3rd-generation autocorrection programming language.  CORC was
the 1962 version and CUPL was the 1966 version (same date as DWIM), neither
of them based on PL/I.  There is an implementation of both at <
http://www.catb.org/~esr/cupl/>.

The Wikipedia DWIM article also points to Magit, the Emacs git client.

>
> In that environment, the benefit from possibly guessing an error
> correction right meant fewer trips to the card reader. In my youth I
> did a fair amount of programming that way in WATFOR/WATFIV and Algol W
> where we really tried to get the programs right since we wanted to
> finish up and go home.
>
> When I was using interactive systems where you could fix one bug and
> try again, over and over, it seemed like cheating.
>
> R's,
> John
>

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[TUHS] Re: The 'usage: ...' message. (Was: On Bloat...)

[Stuff Received]

On 2024-05-19 20:58, Rob Pike wrote:
> The Cornell PL/I compiler, PL/C, ran on the IBM 360 so of course used 
> batch input. It tried automatically to keep things running after a 
> parsing error by inserting some token - semicolon, parenthesis, whatever 
> seemed best - and continuing to parse, in order to maximize the amount 
> of input that could be parsed before giving up. At least, that's what I 
> took the motivation to be. It rarely succeeded in fixing the actual 
> problem, despite PL/I being plastered with semicolons, but it did tend 
> to ferret out more errors per run. I found the tactic helpful.
> 
> -rob
> 

Possibly way off topic but Toronto allowed anyone to run PL/C decks for 
free, which I often did.  One day, they decided to allow all of the card 
to be read as text and my card numbers generated all sorts of errors. 
(At least easily fixed by a visit the card punch.)

S.