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

[Paul Winalski <paul.winalski@gmail.com>]

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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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