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GNU Bison is a general-purpose parser generator that converts an annotated
context-free grammar into a deterministic LR or generalized LR (GLR) parser
employing LALR(1) parser tables.  Bison can also generate IELR(1) or
canonical LR(1) parser tables.  Once you are proficient with Bison, you can
use it to develop a wide range of language parsers, from those used in
simple desk calculators to complex programming languages.

Bison is upward compatible with Yacc: all properly-written Yacc grammars
work with Bison with no change.  Anyone familiar with Yacc should be able to
use Bison with little trouble.  You need to be fluent in C, C++, D or Java
programming in order to use Bison.

Bison and the parsers it generates are portable, they do not require any
specific compilers.

GNU Bison's home page is https://gnu.org/software/bison/.

# Installation
## Build from git
The [README-hacking.md file](README-hacking.md) is about building, modifying
and checking Bison.  See its "Working from the Repository" section to build
Bison from the git repo.  Roughly, run:

    $ git submodule update --init
    $ ./bootstrap

then proceed with the usual `configure && make` steps.

## Build from tarball
See the [INSTALL file](INSTALL) for generic compilation and installation
instructions.

Bison requires GNU m4 1.4.6 or later.  See
https://ftp.gnu.org/gnu/m4/m4-1.4.6.tar.gz.

## Running a non installed bison
Once you ran `make`, you might want to toy with this fresh bison before
installing it.  In that case, do not use `src/bison`: it would use the
*installed* files (skeletons, etc.), not the local ones.  Use `tests/bison`.

## Colored diagnostics
As an experimental feature, diagnostics are now colored, controlled by the
`--color` and `--style` options.

To use them, install the libtextstyle library, 0.20.5 or newer, before
configuring Bison.  It is available from https://alpha.gnu.org/gnu/gettext/,
for instance https://alpha.gnu.org/gnu/gettext/libtextstyle-0.20.5.tar.gz,
or as part of Gettext 0.21 or newer, for instance
https://ftp.gnu.org/gnu/gettext/gettext-0.21.tar.gz.

The option --color supports the following arguments:
- always, yes: Enable colors.
- never, no: Disable colors.
- auto, tty (default): Enable colors if the output device is a tty.

To customize the styles, create a CSS file, say `bison-bw.css`, similar to

    /* bison-bw.css */
    .warning   { }
    .error     { font-weight: 800; text-decoration: underline; }
    .note      { }

then invoke bison with `--style=bison-bw.css`, or set the `BISON_STYLE`
environment variable to `bison-bw.css`.

In some diagnostics, bison uses libtextstyle to emit special escapes to
generate clickable hyperlinks.  The environment variable
`NO_TERM_HYPERLINKS` can be used to suppress them.  This may be useful for
terminal emulators which produce garbage output when they receive the escape
sequence for a hyperlink. Currently (as of 2020), this affects some versions
of emacs, guake, konsole, lxterminal, rxvt, yakuake.

## Relocatability
If you pass `--enable-relocatable` to `configure`, Bison is relocatable.

A relocatable program can be moved or copied to a different location on the
file system.  It can also be used through mount points for network sharing.
It is possible to make symlinks to the installed and moved programs, and
invoke them through the symlink.

See "Enabling Relocatability" in the documentation.

## Internationalization
Bison supports two catalogs: one for Bison itself (i.e., for the
maintainer-side parser generation), and one for the generated parsers (i.e.,
for the user-side parser execution).  The requirements between both differ:
bison needs ngettext, the generated parsers do not.  To simplify the build
system, neither are installed if ngettext is not supported, even if
generated parsers could have been localized.  See
https://lists.gnu.org/r/bug-bison/2009-08/msg00006.html for more
details.

# Questions
See the section FAQ in the documentation (doc/bison.info) for frequently
asked questions.  The documentation is also available in PDF and HTML,
provided you have a recent version of Texinfo installed: run `make pdf` or
`make html`.

If you have questions about using Bison and the documentation does not
answer them, please send mail to <[email protected]>.

# Bug reports
Please send bug reports to <[email protected]>.  Be sure to include the
version number from `bison --version`, and a complete, self-contained test
case in each bug report.

# Copyright statements
For any copyright year range specified as YYYY-ZZZZ in this package, note
that the range specifies every single year in that closed interval.

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Copyright (C) 1992, 1998-1999, 2003-2005, 2008-2015, 2018-2021 Free
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This file is part of GNU bison, the GNU Compiler Compiler.

Permission is granted to copy, distribute and/or modify this document
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