Re: Bison Success Stories?

[Matthew C. Tedder]

Yes,

  I also understood that you can use bison to write commercial software that
is not subject to the GPL.

However, I'd much rather write GPL software.  I've written a little
interpreter already.

Does anyone know of any book or tutorial of some kind that explains how to
make an actual compiler with flex/bison?  O'reilly's lex & yacc only tells
how to make lexical scanners and grammar parsers--not how to make a
compiler, unless I'm missing something.  I can find no such web resource
either.

--Matthew

----- Original Message -----
From: "Akim Demaille" <address@hidden>
To: "Pascal Bart" <address@hidden>
Cc: "Bob Wilkinson" <address@hidden>; <address@hidden>
Sent: Thursday, February 14, 2002 6:08 AM
Subject: Re: Bison Success Stories?


> >>>>> "Pascal" == Pascal Bart <address@hidden> writes:
>
> Pascal> Hi,
> >> My company is using Bison on a project for a very particular
> >> customer.  If we use non-commercial software we have to somehow
> >> 'prove' that the software works (because if it doesn't they have no
> >> one blame, it's stupid, I know).  The best way I can come up with
> >> to show that Bison is the reliable tool I know it to be is to list
> >> some commercial applications where Bison is used, preferably
> >> something with a safety aspect to it.
>
> Pascal> Bison is working fine, its generated parser are used in mysql,
> Pascal> bash, gcc, and more, but I would to remember you that Bison
> Pascal> generated parsers are under GPL license, so it cann't be
> Pascal> include in a commercial application, because GPL source code
> Pascal> can _only_ be used in a GPL application, for more information
> Pascal> see http://www.gnu.org/licenses/gpl.txt.
>
> This is *wrong*.
>
> Thanks God, this is dead wrong: read the f*g license!
>
>
> bison.simple:
>
> /* As a special exception, when this file is copied by Bison into a
>    Bison output file, you may use that output file without restriction.
>    This special exception was added by the Free Software Foundation
>    in version 1.24 of Bison.  */
>
>
>
>
> bison.texi:
>
> Conditions for Using Bison
> **************************
>
>    As of Bison version 1.24, we have changed the distribution terms for
> `yyparse' to permit using Bison's output in nonfree programs.
> Formerly, Bison parsers could be used only in programs that were free
> software.
>
>    The other GNU programming tools, such as the GNU C compiler, have
> never had such a requirement.  They could always be used for nonfree
> software.  The reason Bison was different was not due to a special
> policy decision; it resulted from applying the usual General Public
> License to all of the Bison source code.
>
>    The output of the Bison utility--the Bison parser file--contains a
> verbatim copy of a sizable piece of Bison, which is the code for the
> `yyparse' function.  (The actions from your grammar are inserted into
> this function at one point, but the rest of the function is not
> changed.)  When we applied the GPL terms to the code for `yyparse', the
> effect was to restrict the use of Bison output to free software.
>
>    We didn't change the terms because of sympathy for people who want to
> make software proprietary.  *Software should be free.*  But we
> concluded that limiting Bison's use to free software was doing little to
> encourage people to make other software free.  So we decided to make the
> practical conditions for using Bison match the practical conditions for
> using the other GNU tools.
>
>
>
> Now, to answer the question, I'd submit the following paragraph.
>
> What is Bison
> =============
>
>    Yacc is a generator of efficient parsers.  A "parser" is a program
> or routine which recognizes the structure of sentences.  Yacc's input is
> composed of "rules" with associated actions.  The rules must be
> "context free", i.e., their left hand side is composed of a single
> nonterminal symbol, and their right hand side is composed of series of
> terminal and nonterminal symbols.  When a rule is reduced, the
> associated C code is triggered.
>
>    Yacc is based on pushdown automata.  It is a implementation of the
> LALR(1) parsing algorithm, which is sufficient for most programming
> languages, but can be too limited a framework to describe conveniently
> intricate languages.
>
>    Yacc, and all its declinations (CAMLYacc for CAML etc.) are used in
> numerous applications, especially compilers and interpreters.  Hence its
> name: Yet Another Compiler Compiler.
>
>
>    Bison is a free software implementation of Yacc, as described by the
> POSIX standard.  It provides a wide set of additional options and
> features, produces self contained portable code (no library is
> required), supports a more pleasant syntax, and stands as a standard of
> its own.  Since most Yacc do have problems (inter-Yacc compatibility and
> actual bugs), all the reasons are in favor of using exclusively Bison:
> the portable C code it produces can be shipped in the package and will
> compile cleanly on the user's machine.  It imposes no restriction on the
> license of the produced parser.
>
>    It is used by the GNU Compiler Collection for C, C++(1), the C
> preprocessor.  Many other programming language tools use Bison or Yacc:
> GNU AWK, Perl, but it proves itself useful in reading structured files:
> a2ps uses it to parse its style sheets.  It also helps decoding some
> limited forms of natural language: numerous GNU utilities use a Yacc
> grammar to decode dates such as `2 days ago', `3 months 1 day', `25
> Dec', `1970-01-01 00:00:01 UTC +5 hours' etc.
>
>    GNU Gettext deserves a special mention with three different uses:
> one to parse its input files, another one to parse the special comments
> in these files, and one to evaluate the foreign language dependent rules
> defining the plural forms.
>
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