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Re: Parsing partial sentences

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On Fri, 7 Apr 2017 22:24:04 +0200, Hans-Peter Diettrich
<DrDiettrich1@netscape.net> wrote:

>Am 07.04.2017 um 18:59 schrieb George Neuner:
>
>> It might be easiest to just run the C preprocessor as a 1st pass and
>> then attempt to convert the result.
>
>That would obfuscate the source code widely :-(

That's true, but any C code you might encounter could, in itself, be
arbitrarily convoluted and hard to understand: e.g., deep pointer
chains, goto spaghetti, Duff devices, setjmp/longjmp, coroutines, etc.

I understand that you want to be able to preserve and relate the
original source to the translation, but I don't see any other real
choice other than to employ the C preprocessor.  As John said, a
#define body may not even be a complete expression - nevermind a legal
one.

Normally a parser would error on an illegal or incomplete expression.
Creating a parser that can return useful information about arbitrary
quasi-legal input I think would be extremely difficult.


>> Since a #define body is just text, it can be anything - people have
>> created whole DSLs using #define.  If you really need to figure them
>> out, I'm afraid you'll need (almost) the whole C language parser to do
>> it.
>
>I already wrote the parser, but it's LL. For code snippets a LR parser
>looks like the only solution?

You could do it in either LL or LR ... LR would be more runtime
efficient, but I think it would not be any easier to create the parser
in the first place.

To do what you want you'd need non-terminals not just for every legal
(sub)expression in C, but for every individual keyword, operator and
symbol, and also for any quasi-legal combination of them.  The parser
would be enormous.


Building on John's example, consider what you'd do with

# define FOO +
# define BAR + 42
# define BAZ + c   /* note 'c' is undefined */
int a, b;

    :
    a = a FOO b BAR BAZ;
    :


And then consider what you'd need to handle sh..stuff like this for
every keyword, operator, variable, etc.

George

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Thread

Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-03 09:57 +0200
  Re: Parsing partial sentences Fernando <pronesto@gmail.com> - 2017-04-04 06:05 -0700
    Re: Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-07 11:16 -0400
      Re: Parsing partial sentences George Neuner <gneuner2@comcast.net> - 2017-04-07 12:59 -0400
        Re: Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-07 22:24 +0200
          Re: Parsing partial sentences George Neuner <gneuner2@comcast.net> - 2017-04-10 20:22 -0400
            Re: Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-11 10:31 +0200
              Re: Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-11 19:40 +0200
              Re: Parsing partial sentences George Neuner <gneuner2@comcast.net> - 2017-04-11 23:05 -0400
                Re: Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-12 13:45 +0200
          Re: Parsing partial sentences Martin Ward <martin@gkc.org.uk> - 2017-04-11 10:30 +0100
  Re: Parsing partial sentences Walter Banks <walter@bytecraft.com> - 2017-04-27 10:58 -0400
    Re: Parsing partial sentences Kaz Kylheku <686-678-9105@kylheku.com> - 2017-04-27 19:08 +0000
      Re: Parsing partial sentences rugxulo@gmail.com - 2017-04-28 16:32 -0700
      Re: Parsing partial sentences Marco van de Voort <marcov@toad.stack.nl> - 2017-04-29 14:57 +0000
        Re: Parsing partial sentences Kaz Kylheku <686-678-9105@kylheku.com> - 2017-04-30 16:31 +0000
    Re: Parsing partial sentences Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2017-04-28 02:48 +0200

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