Questions about parser state

Questions about parser state

[Xue Fuqiao]

Hi,

I have two questions about parser state in Emacs Lisp.  In (info
"(elisp) Parser State"):

   Here are the meanings of the elements of the parser state:
[...]
  5. ‘t’ if the end point is just after a quote character.
[...]
  7. What kind of comment is active: ‘nil’ if not in a comment or in a
     comment of style ‘a’;

My question is:
1. What does the "quote character" mean?  Does it mean "'" in Lisp?  If
   so, what about "," and "#"?
2. What is comment style ‘a’?  In (info "(elisp) Syntax Flags"): "A
   comment style is a set of flags ‘b’, ‘c’, and ‘n’, so there can be up
   to 8 different comment styles."  I can't find an ‘a’ style.

I've also searched the archives/web, but didn't get anything that looked
promising.  Can anyone point me in the right direction?

-- 
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/

Re: Questions about parser state

[Stefan Monnier]

> 1. What does the "quote character" mean?  Does it mean "'" in Lisp?  If
>    so, what about "," and "#"?

No, it's typically the \ char.

> 2. What is comment style ‘a’?  In (info "(elisp) Syntax Flags"): "A
>    comment style is a set of flags ‘b’, ‘c’, and ‘n’, so there can be up
>    to 8 different comment styles."  I can't find an ‘a’ style.

`a' is the comment style when neither `b' nor `c' is present.


        Stefan

Re: Questions about parser state

[Xue Fuqiao]

On Sat, Oct 5, 2013 at 10:08 AM, Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
>> 1. What does the "quote character" mean?  Does it mean "'" in Lisp?  If
>>    so, what about "," and "#"?
>
> No, it's typically the \ char.
>
>> 2. What is comment style ‘a’?  In (info "(elisp) Syntax Flags"): "A
>>    comment style is a set of flags ‘b’, ‘c’, and ‘n’, so there can be up
>>    to 8 different comment styles."  I can't find an ‘a’ style.
>
> `a' is the comment style when neither `b' nor `c' is present.

I see, thank you.  To make it clearer, what about the following patch?

=== modified file 'doc/lispref/syntax.texi'
*** doc/lispref/syntax.texi    2013-10-03 15:32:10 +0000
--- doc/lispref/syntax.texi    2013-10-05 10:07:16 +0000
***************
*** 339,349 ****
  @cindex comment style
  Emacs supports several comment styles simultaneously in any one syntax
  table.  A comment style is a set of flags @samp{b}, @samp{c}, and
! @samp{n}, so there can be up to 8 different comment styles.
! Each comment delimiter has a style and only matches comment delimiters
! of the same style.  Thus if a comment starts with the comment-start
! sequence of style ``bn'', it will extend until the next matching
! comment-end sequence of style ``bn''.

  The appropriate comment syntax settings for C++ can be as follows:

--- 339,350 ----
  @cindex comment style
  Emacs supports several comment styles simultaneously in any one syntax
  table.  A comment style is a set of flags @samp{b}, @samp{c}, and
! @samp{n}, so there can be up to 8 different comment styles.  When
! neither @samp{b} nor @samp{c} is present, the comment style is
! @samp{a}.  Each comment delimiter has a style and only matches comment
! delimiters of the same style.  Thus if a comment starts with the
! comment-start sequence of style ``bn'', it will extend until the next
! matching comment-end sequence of style ``bn''.

  The appropriate comment syntax settings for C++ can be as follows:

***************
*** 838,844 ****

  @item
  @cindex quote character
! @code{t} if the end point is just after a quote character.

  @item
  The minimum parenthesis depth encountered during this scan.
--- 839,845 ----

  @item
  @cindex quote character
! @code{t} if the end point is just after an escape-syntax character.

  @item
  The minimum parenthesis depth encountered during this scan.

-- 
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/

Re: Questions about parser state

[Stefan Monnier]

> ! @samp{n}, so there can be up to 8 different comment styles.  When
> ! neither @samp{b} nor @samp{c} is present, the comment style is
> ! @samp{a}.  Each comment delimiter has a style and only matches comment

Actually, the use of `a' is problematic, indeed.
Since we really have 8 styles: "", "b", "c", "bc", "n", "bn", "cn", "bcn".
So, "a" doesn't fit very well in there.
It's inherited from earlier times where we had just "" and "b", so ""
could be considered as "a".

So we should probably get rid of the "style `a'" terminology and replace
it with something else.


        Stefan

RE: Questions about parser state

[Drew Adams]

> > 1. What does the "quote character" mean?  Does it mean "'" in Lisp?  If
> >    so, what about "," and "#"?
> 
> No, it's typically the \ char.

Though char escaping is a type of quoting, would it be clearer to refer
to \ as the escape character?  That's common language, and it is what we
do when talking about regexps (e.g., (elisp) `Syntax Descriptors': "Thus,
`\' as a designator character always means "escape character" syntax...."