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Re: Labels

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On 08/15/2015 07:47 PM, Ben Bacarisse wrote:
> James Kuyper <jameskuyper@verizon.net> writes:
> 
>> On 08/15/2015 06:44 PM, Ben Bacarisse wrote:
>>> Bartc <bc@freeuk.com> writes:
>>> <snip>
>>>> Is 'A*B' an expression, or is it declaring a variable B of type
>>>> pointer-to-A?
>>>>
>>>> Is 'F(G)' a function call to G with argument G, or is it declaring a
>>>> variable G of type F, or is it the start of function declaration, or
>>>> the start of function definition?
>>>>
>>>> I think you have your work cut out!
>>>
>>> This makes it sound as if C is particularly hard to parse, but it isn't,
>>> provided you know how to handle typedefs.  After reading a typedef, the
>>> parser must mark the identifiers involved as referring to types.
>>
>> As earlier messages in this thread have shown, you can't always do that
>> immediately after parsing the identifier - the identifier could be a
>> statement label, and you have to read the next token after the
>> identifier to rule out that possibility.
> 
> I'm taking about what the parse must do once it has parsed a full
> typedef declarator.

So am I. I'm talking about a use of the typedef, not the declaration of
the typedef. After parsing the full typedef declarator, if you find an
identifier with the same name at the start of a new line, it could be
the first token of a declaration, or the first token of a labeled
statement, with a label that happens to be the same as the typedef name.
Therefore, you can't mark it as a type until you've read the next token
and determined that it's not ':'.

> ... I don't see any connection with the original issue
> of labels.

Until you read the following ':', you can't distinguish a label that has
the same name as a typedef from a typedef used as the first token of a
declaration. And that's one of the three reasons (the other two are
object names and function names) why the ':' must (in some cases) be
read before a statement label can be unambiguously identified as such.

>> This doesn't strike me as a big
>> problem, but David Kleinecke finds it so.
> 
> Yes, any introductory book on parsing will explain how to handle
> look-ahead for languages like C.  They won't all explain the typedef
> issue which is why I tried to explain it.

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Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-15 09:46 -0700
  Re: Labels James Kuyper <jameskuyper@verizon.net> - 2015-08-15 14:49 -0400
    Re: Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-15 18:48 -0700
  Re: Labels Bartc <bc@freeuk.com> - 2015-08-15 18:27 +0100
    Re: Labels Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-15 23:44 +0100
      Re: Labels James Kuyper <jameskuyper@verizon.net> - 2015-08-15 19:04 -0400
        Re: Labels Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-16 00:47 +0100
          Re: Labels James Kuyper <jameskuyper@verizon.net> - 2015-08-15 20:20 -0400
            Re: Labels Bartc <bc@freeuk.com> - 2015-08-16 01:56 +0100
              Re: Labels Keith Thompson <kst-u@mib.org> - 2015-08-15 19:47 -0700
                Re: Labels James Kuyper <jameskuyper@verizon.net> - 2015-08-16 11:59 -0400
            Re: Labels Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-16 22:42 +0100
              Re: Labels James Kuyper <jameskuyper@verizon.net> - 2015-08-16 20:39 -0400
                Re: Labels Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-17 03:16 +0100
        Re: Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-15 19:01 -0700
      Re: Labels Bartc <bc@freeuk.com> - 2015-08-16 01:11 +0100
        Re: Labels Keith Thompson <kst-u@mib.org> - 2015-08-15 19:13 -0700
          Re: Labels Bartc <bc@freeuk.com> - 2015-08-16 10:34 +0100
            Re: Labels Keith Thompson <kst-u@mib.org> - 2015-08-16 13:58 -0700
            Re: Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-16 20:42 -0700
              Re: Labels Keith Thompson <kst-u@mib.org> - 2015-08-16 21:24 -0700
                Re: Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-17 18:01 -0700
              Re: Labels Bartc <bc@freeuk.com> - 2015-08-17 11:04 +0100
        Re: Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-15 19:04 -0700
        Re: Labels Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-08-16 23:55 +0100
    Re: Labels David Kleinecke <dkleinecke@gmail.com> - 2015-08-15 19:00 -0700

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