Groups | Search | Server Info | Keyboard shortcuts | Login | Register

Groups > comp.compilers > #273

Re: coupling LALR with a scanner?

Show key headers only | View raw

"Paul B Mann"  a icrit dans le message de groupe de discussion :
>> IELR was exactly made for that reason, as a first step to PSLR: some
>IELR(1) does not solve this problem.  It solves the problem of reduce-
>reduce conflicts in an LR(0) [...]

OK I did not sentenced that right, this is PSLR which does all the
lexer/parser integration (hence Pseudo Scannerless LR).

>What you described with Javascript is a little language inside of
>another language.  Why not switch parsers when a slash ('/') is
>encountered if necessary?

The problem is that / is used as a normal token AND as the start for regular
expression.
For example these are two valid sequences:
var regexpr = / b + a /
                    2;
var numeric_var = 1 / b + a /
                    2;

The 2; on the following lines will have two different meanings, in case
'regexpr', it is an instruction setting the expression value (as used in
eval() ), in the case second case, 2 is the second operand to a / operator.

I insist a bit on this to show there is no 'right side' heuristic to
determine / b + a / is a regular expression. On the other hand the '1'
expression could be as complex as you can imagine.

Of course in the presence of something like expr / expr the parser knows the
/ is for a division, and if the / is found where expr is expected it knows
there is a regular expression coming.
I don't see how I could hack this into a scanner only. maybe some specific
preceding tokens. I have pass again some time on that question.

Armel

Back to comp.compilers | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-07-05 01:02 +0200
  Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-07-07 10:28 +0200
    coupling LALR with a scanner? "Karsten Nyblad" <uu3kw29sb7@snkmail.com> - 2011-07-07 10:46 +0200
    Re: coupling LALR with a scanner? "Karsten Nyblad" <uu3kw29sb7@snkmail.com> - 2011-07-08 14:39 +0200
      Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-08-04 11:17 +0200
        Re: coupling LALR with a scanner? Paul B Mann <paul@paulbmann.com> - 2011-09-13 13:38 -0700
          Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-09-16 10:47 +0200
            Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-09-19 13:52 +0200
            Re: coupling LALR with a scanner? Paul B Mann <paul@paulbmann.com> - 2011-09-19 12:12 -0700
              Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-09-20 09:40 +0200
                Re: coupling LALR with a scanner? Chris Dodd <cdodd@acm.org> - 2011-09-23 23:59 +0100
                Re: coupling LALR with a scanner? Chris F Clark <cfc@shell01.TheWorld.com> - 2011-09-29 00:00 -0400
                Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-10-02 16:41 +0200
                Re: coupling LALR with a scanner? Chris F Clark <cfc@shell01.TheWorld.com> - 2011-10-03 11:59 -0400
                Re: coupling LALR with a scanner? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-10-03 21:08 +0000
          Re: coupling LALR with a scanner? Paul B Mann <paul@paulbmann.com> - 2011-09-17 10:38 -0700

csiph-web