Re: Improved accuracy in diagnostics. Is it worthwhile?

Ev. Drikos <drikosev@gmail.com> schrieb:


> This is mainly a parsing question but it's also Fortran related as well.


[...]


> So far, my approach has been that improved diagnostics shouldn't slow
> down the processing of correct programs.


With today's computer speeds, this is likely not a very important
consideration any more.


If you are compiling, it is usually a small fraction of time that
is spent in the parsing, and much more in optimization and code
generation. An example: Compiling a 50 k line Fortran program with
"gfortran -O2" takes 17.4 seconds on the computer I type this on.
Checking with "gfortran -fsyntax-only" takes 4.2 seconds. (For
those who want to reproduce: aermod.f90 from the Polyhedron suite).


50k lines for a single source files is already quite a lot (much
longer than most source files for modular programs are likely to
be) and throwing a bit more CPU time at the problem to reduce user
confusion by emitting better error messages is extremely likely
to be a win for the user. Just be careful to avoid anything
worse than O(n log n) for code size, or somebody will come
along with a test case that takes _really_ long.


(Take the above with a grain of salt for C++ headers.)




> Is it worthwhile to improve
> diagnostics by disabling default actions in a LALR parser?


I would presume so. Run a few benchmarks and find out.
[In my experience, lexing and optimization take most of the
time, and parsing is insignificant. -John]

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