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

[Douglas McIlroy <douglas.mcilroy@dartmouth.edu>]

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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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