tools/re2c/README

re2c
----

Version 0.9.1
Originally written by Peter Bumbulis (peterr@csg.uwaterloo.ca)
Currently maintained by Brian Young (bayoung@acm.org)

The re2c distribution can be found at:

    http://www.tildeslash.org/re2c/index.html

The source distribution is available from:

    http://www.tildeslash.org/re2c/re2c-0.9.1.tar.gz

This distribution is a cleaned up version of the 0.5 release
maintained by me (Brian Young).  Several bugs were fixed as well
as code cleanup for warning free compilation.  It has been developed
and tested with egcs 1.0.2 and gcc 2.7.2.3 on Linux x86.  Peter
Bumbulis' original release can be found at:

    ftp://csg.uwaterloo.ca/pub/peterr/re2c.0.5.tar.gz

re2c is a great tool for writing fast and flexible lexers.  It has
served many people well for many years and it deserves to be
maintained more actively.  re2c is on the order of 2-3 times faster
than a flex based scanner, and its input model is much more
flexible.

Patches and requests for features will be entertained.  Areas of
particular interest to me are porting (a Solaris and an NT
version will be forthcoming) and wide character support.  Note
that the code is already quite portable and should be buildable
on any platform with minor makefile changes.

Peter's original version 0.5 ANNOUNCE and README follows.

Brian

--

re2c is a tool for generating C-based recognizers from regular
expressions.  re2c-based scanners are efficient:  for programming
languages, given similar specifications, an re2c-based scanner is
typically almost twice as fast as a flex-based scanner with little or no
increase in size (possibly a decrease on cisc architectures).  Indeed,
re2c-based scanners are quite competitive with hand-crafted ones.

Unlike flex, re2c does not generate complete scanners:  the user must
supply some interface code.  While this code is not bulky (about 50-100
lines for a flex-like scanner; see the man page and examples in the
distribution) careful coding is required for efficiency (and
correctness).  One advantage of this arrangement is that the generated
code is not tied to any particular input model.  For example, re2c
generated code can be used to scan data from a null-byte terminated
buffer as illustrated below.

Given the following source

    #define NULL            ((char*) 0)
    char *scan(char *p){
    char *q;
    #define YYCTYPE         char
    #define YYCURSOR        p
    #define YYLIMIT         p
    #define YYMARKER        q
    #define YYFILL(n)
    /*!re2c
	    [0-9]+          {return YYCURSOR;}
	    [\000-\377]     {return NULL;}
    */
    }

re2c will generate

    /* Generated by re2c on Sat Apr 16 11:40:58 1994 */
    #line 1 "simple.re"
    #define NULL            ((char*) 0)
    char *scan(char *p){
    char *q;
    #define YYCTYPE         char
    #define YYCURSOR        p
    #define YYLIMIT         p
    #define YYMARKER        q
    #define YYFILL(n)
    {
	    YYCTYPE yych;
	    unsigned int yyaccept;
	    goto yy0;
    yy1:    ++YYCURSOR;
    yy0:
	    if((YYLIMIT - YYCURSOR) < 2) YYFILL(2);
	    yych = *YYCURSOR;
	    if(yych <= '/') goto yy4;
	    if(yych >= ':') goto yy4;
    yy2:    yych = *++YYCURSOR;
	    goto yy7;
    yy3:
    #line 10
	    {return YYCURSOR;}
    yy4:    yych = *++YYCURSOR;
    yy5:
    #line 11
	    {return NULL;}
    yy6:    ++YYCURSOR;
	    if(YYLIMIT == YYCURSOR) YYFILL(1);
	    yych = *YYCURSOR;
    yy7:    if(yych <= '/') goto yy3;
	    if(yych <= '9') goto yy6;
	    goto yy3;
    }
    #line 12

    }

Note that most compilers will perform dead-code elimination to remove
all YYCURSOR, YYLIMIT comparisions.

re2c was developed for a particular project (constructing a fast REXX
scanner of all things!) and so while it has some rough edges, it should
be quite usable.  More information about re2c can be found in the
(admittedly skimpy) man page; the algorithms and heuristics used are
described in an upcoming LOPLAS article (included in the distribution).
Probably the best way to find out more about re2c is to try the supplied
examples.  re2c is written in C++, and is currently being developed
under Linux using gcc 2.5.8.

Peter

--

re2c is distributed with no warranty whatever.  The code is certain to
contain errors.  Neither the author nor any contributor takes
responsibility for any consequences of its use.

re2c is in the public domain.  The data structures and algorithms used
in re2c are all either taken from documents available to the general
public or are inventions of the author.  Programs generated by re2c may
be distributed freely.  re2c itself may be distributed freely, in source
or binary, unchanged or modified.  Distributors may charge whatever fees
they can obtain for re2c.

If you do make use of re2c, or incorporate it into a larger project an
acknowledgement somewhere (documentation, research report, etc.) would
be appreciated.

Please send bug reports and feedback (including suggestions for
improving the distribution) to

			peterr@csg.uwaterloo.ca

Include a small example and the banner from parser.y with bug reports.