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Re: Are compiler developers light-years ahead of other software development?

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On 2022-01-22, Roger L Costello <costello@mitre.org> wrote:
> Kaz Kylheku wrote this about the C++ compiler:
>
>> In other words, a major compiler for probably
>> the programming language with the most
>> complicated syntax ever, eschews pretty much
>> all that we have learned and accumulated about
>> parsing between around 1968 and now.
>
> Yikes!
>
> They ignored the rich theory and vast set of algorithms, in favor of
> their own proprietary code? Why would the C++ compiler developers do
> such a thing?

Wild guess:

Suppose that there is a foo_statement which contains a bar_designator,
and something is wrong in there. They can fire up gdb, and put a simple
breakpoint on bar_designator, feed in the test case and get a call stack
in which parse_bar_designator is called by parse_foo_statement.
They can examine all the locals, and arguments up the stack.

Typically, nothing like this is easily possible with the
theoretically-based parser generation tools.

And in C++, you're likely going to be debugging parsing quite a bit.

The main parser generation tools used by GNU projects are Flex and
Bison. These tools are moving targets; especially Bison. The common
practice is to ship the generated parser.

(In a fundamental compiler project, you have to for other reasons, like
the users not having thta tool installed, because maybe they need your
compiler to build it: you want as few dependencies as possible.)

Now GCC is hacked on quite a bit and has lots of contributors. It would
be annoying to tell people "Oh, just use the generated, shipped
parsers if you're not touching the grammar; if you need to regenerate,
please use the exact version Bison X.Y.Z.".

If a  parser is hand-written, that whole sort of problem goes away.

> /Roger
> [My guess is that they were too busy chopping down trees to sharpen their axes. -John]

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

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Are compiler developers light-years ahead of other software development? Roger L Costello <costello@mitre.org> - 2022-01-16 14:36 +0000
  Re: Are compiler developers light-years ahead of other software development? Philipp Klaus Krause <pkk@spth.de> - 2022-01-16 22:13 +0100
  Re: Are compiler developers light-years ahead of other software development? gah4 <gah4@u.washington.edu> - 2022-01-17 07:14 -0800
  Re: Are compiler developers light-years ahead of other software development? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2022-01-19 21:33 +0000
  Re: Are compiler developers light-years ahead of other software development? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-22 03:01 +0000
    Re: Are compiler developers light-years ahead of other software development? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2022-01-22 10:43 +0000
      Re: Are compiler developers light-years ahead of other software development? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-22 21:38 +0000
    Re: Are compiler developers light-years ahead of other software development? Roger L Costello <costello@mitre.org> - 2022-01-22 12:50 +0000
      Re: Are compiler developers light-years ahead of other software development? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-22 21:22 +0000
      Re: Are compiler developers light-years ahead of other software development? Ian Lance Taylor <ianlancetaylor@gmail.com> - 2022-01-22 15:40 -0800
        Re: Are compiler developers light-years ahead of other software development? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-23 06:17 +0000

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