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RE: 2 character comment starter bug

From: Bielawski, Richard G.
Subject: RE: 2 character comment starter bug
Date: Wed, 23 Mar 2005 18:28:42 -0800

> >> >     (modify-syntax-entry ?\= "_ b12" st) ; comment start == 
> >> 
> >> Yes, it seems the problem is that your 2-char comment  
> sequence is made
> >> of symbol-chars, so there are cases where the code does 
> things  like "oh,
> >> here's a symbol, let's skip it" without checking whether 
> some of the
> >> chars that compose the symbol happen to also be a comment-marker.
> >> 
> >> Does your = char really need to have "symbol" syntax (i.e. "_") or
> >> could it have punctuation syntax instead (i.e. ".") ?
> > Punctuation syntax seems to cause all kinds of problems.  The =
> > character is commonly used as the first character in in
> > filenames.
> But does it matter in such a case whether it has punctuation syntax or
> symbol syntax?  Do you also give symbol syntax to the / 
> directory separator as well?

A / is an illegal character in any part of a filename on this system.
In this language / / are most often seen as paired delimiters.

> > It's also part of several operators such as := and ':=' and 
> '=:' which
> > would behave quite oddly without proper syntax.
> Traditionally, punctuation syntax has been used specifically 
> for things like
> the above.  So, I'd say that punctuation *is* the proper 
> syntax.  If you use
> symbol syntax for those chars, things like M-C-f risk skipping over
> "foo:=bar" in "foo:=bar + 1", rather than just skipping over "foo".

[#set foo [bar]] and [#set foo [#compute bar + 1]] would be required
to accomplish the operations your examples seem to describe. 
If I see ':=' in this language I would almost certainly want it 
treated as a word.

> > It sounds like you are saying it might be a problem to fix the code.
> Yes: it might take a bit of work; it risks slowing down syntax-based
> operations in all buffers; and it could introduce bugs in 
> other languages
> where the current behavior is closer to what we want (after 
> all, if you
> define your language using lex and you say that a symbol can 
> be [a-z=_]+
> and a comment starter is ==, your lexer will take `foo==' to 
> be a symbol
> and won't see the comment starter in it).

In this language == always begins a comment no matter where it is
found unless a ~ precedes it.  There are no exceptions.

> The current behavior is buggy (it doesn't behave consistently between
> things like forward-sexp, backward-sexp, and parse-partial-sexp).
> But before someone can convince me to try and fix these bugs, 
> they should
> first make a good case that the way they setup their 
> syntax-tables is well
> thought out.

If the fact that the problem exists reflects the standard by
which `well thought out' is measured you're being a pushover.

I suppose, since it's possible for me to work around this problem
by using syntactic-keywords to handle the comments I would prefer 
problems for which there are no workarounds be addressed first.  
If it will remain this way for any length of time though, I do
think it should be documented somewhere.  Even if only on a known
problems list.

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