A different comment syntax question

[Rob Cameron]

Makoto replies:
> Rob Cameron wrote:
> > 
> > If, as I assume, the answer is that only the double hyphen case
> > is a concern, then the grammar needs to be changed.
> > 
> >    Comment ::= '<!--' (Char* - (Char* '--' Char*)) '-->'
> > 
> 
> This is semantically identical to the current rule:
> 
>  Comment ::= '<!--' ((Char - '-') | ('-' (Char - '-')))* '-->'
> 

No, I don't think it is equivalent.  Proof:
  (a)  No string in (Char - '-') ends with a hyphen.  (This is the
         set of all single character strings except the hyphen.)
  (b)  Thus, no string in ('-' (Char - '-')) ends with a hyphen.
  (c)  Thus, no string in ((Char - '-') | ('-' (Char - '-'))) ends 
       with a hyphen.
  (d)  Thus, no string in ((Char - '-') | ('-' (Char - '-')))* ends 
       with a hyphen.  

Robert D. Cameron, Associate Professor           cameron at cs.sfu.ca
School of Computing Science                      FAX: (604) 291-3045
Simon Fraser University
Burnaby, B.C., Canada  V5A 1S6

Internet Electronic Library Project at SFU       
http://elib.cs.sfu.ca/


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