--- yapps2-2.2.1.orig/Yapps2.egg-info/PKG-INFO +++ yapps2-2.2.1/Yapps2.egg-info/PKG-INFO @@ -0,0 +1,65 @@ +Metadata-Version: 1.2 +Name: Yapps2 +Version: 2.2.1 +Summary: Yet Another Python Parser System +Home-page: https://github.com/smurfix/yapps +Author: Amit J. Patel, Matthias Urlichs +Author-email: amitp@cs.stanford.edu, smurf@debian.org +Maintainer: Matthias Urlichs +Maintainer-email: smurf@debian.org +License: MIT +Description: YAPPS: Yet Another Python Parser System + ---------------------------------------- + + For the most complete and excellent documentation (e.g. [manual with + examples](http://theory.stanford.edu/~amitp/yapps/yapps2/manual/)) and info, + please see original project website: http://theory.stanford.edu/~amitp/yapps/ + + YAPPS is an easy to use parser generator that is written in Python and generates + Python code. + There are several parser generator systems already available for Python, but + this parser has different goals: Yapps is simple, very easy to use, and produces + human-readable parsers. + + It is not the fastest or most powerful parser. + Yapps is designed to be used when regular expressions are not enough and other + parser systems are too much: situations where you might otherwise write your own + recursive descent parser. + + This fork contains several upward-compatible enhancements to the original + YAPPS source, originally included in [debian package](http://packages.debian.org/sid/yapps2): + + * Handle stacked input ("include files"). + * Augmented ignore-able patterns (can parse multi-line C comments correctly). + * Better error reporting. + * Read input incrementally. + + + Installation + ---------------------------------------- + + It's a regular package for Python 2.7 (not 3.X, but there are links to 3.X + patches listed on the [original author + website](http://theory.stanford.edu/~amitp/yapps/)), but not in pypi, so can be + installed from a checkout with something like that: + + % python setup.py install + + Better way would be to use [pip](http://pip-installer.org/) to install all the + necessary dependencies as well: + + % pip install 'git+https://github.com/mk-fg/yapps.git#egg=yapps' + + Note that to install stuff in system-wide PATH and site-packages, elevated + privileges are often required. + Use "install --user", + [~/.pydistutils.cfg](http://docs.python.org/install/index.html#distutils-configuration-files) + or [virtualenv](http://pypi.python.org/pypi/virtualenv) to do unprivileged + installs into custom paths. + + Alternatively, `./yapps2` can be run right from the checkout tree, without any + installation. + + No extra package dependencies. + +Platform: UNKNOWN --- yapps2-2.2.1.orig/Yapps2.egg-info/SOURCES.txt +++ yapps2-2.2.1/Yapps2.egg-info/SOURCES.txt @@ -0,0 +1,12 @@ +README.md +setup.py +Yapps2.egg-info/PKG-INFO +Yapps2.egg-info/SOURCES.txt +Yapps2.egg-info/dependency_links.txt +Yapps2.egg-info/entry_points.txt +Yapps2.egg-info/top_level.txt +yapps/__init__.py +yapps/cli_tool.py +yapps/grammar.py +yapps/parsetree.py +yapps/runtime.py \ No newline at end of file --- yapps2-2.2.1.orig/Yapps2.egg-info/dependency_links.txt +++ yapps2-2.2.1/Yapps2.egg-info/dependency_links.txt @@ -0,0 +1 @@ + --- yapps2-2.2.1.orig/Yapps2.egg-info/entry_points.txt +++ yapps2-2.2.1/Yapps2.egg-info/entry_points.txt @@ -0,0 +1,3 @@ +[console_scripts] +yapps2 = yapps.cli_tool:main + --- yapps2-2.2.1.orig/Yapps2.egg-info/top_level.txt +++ yapps2-2.2.1/Yapps2.egg-info/top_level.txt @@ -0,0 +1 @@ +yapps --- yapps2-2.2.1.orig/debian/README +++ yapps2-2.2.1/debian/README @@ -0,0 +1,23 @@ +The Debian Package yapps2 +------------------------- + +This package contains several upward-compatible enhancements to the +original YAPPS source: +- Handle stacked input ("include files") +- augmented ignore-able patterns + (this means that yapps2 now can parse things like multi-line C comments) +- better error reporting +- read input incrementally + +Traditionally, the yapps runtime is called yappsrt.py and it was +installed with the binary that uses the parser. However, as soon as +there is more than one of those, this method breaks. + +Therefore, and because the new runtime isn't entirely compatible to the +old yappsrt.py, I decided to rename the generated parser to +yapps/runtime.py. It is provided by the yapps2-runtime package. +You need to depend on this package if you Debianize Python programs that +use yapps2. + +-- +Matthias Urlichs --- yapps2-2.2.1.orig/debian/changelog +++ yapps2-2.2.1/debian/changelog @@ -0,0 +1,184 @@ +yapps2 (2.2.1-3) unstable; urgency=medium + + * yapps2 depends on python3-pkg-resources for the entry point wrapper + (closes: #913392). + Thanks to Colin Watson. + + -- Matthias Urlichs Sun, 11 Nov 2018 18:49:20 +0100 + +yapps2 (2.2.1-2) unstable; urgency=medium + + * Add setuptools dependencies (closes: #912097). + + -- Matthias Urlichs Mon, 05 Nov 2018 07:26:11 +0100 + +yapps2 (2.2.1-1) unstable; urgency=medium + + * New feature version + * Don't try to run "bk". + * Ignore built files + * Add manpage + * fix packaging + * convert to debhelper + * Clean up Lintian errors + * Add Py3 package + + -- Matthias Urlichs Mon, 15 Oct 2018 11:24:39 +0200 + +yapps2 (2.1.1-17.5) unstable; urgency=medium + + * Non-maintainer upload. + * Move binary-arch rule to binary-indep, since all our binary packages are + Architecture: all. + + -- Colin Watson Tue, 08 Nov 2016 19:48:31 +0000 + +yapps2 (2.1.1-17.4) unstable; urgency=medium + + * Non-maintainer upload. + * Bump to debhelper compat level 9 (closes: #817771). + * Use ${binary:Version} rather than ${Source-Version} (closes: #833233). + + -- Colin Watson Sun, 06 Nov 2016 17:11:44 +0000 + +yapps2 (2.1.1-17.3) unstable; urgency=medium + + * Non-maintainer upload. + * Build using dh-python. Closes: #786242. + + -- Matthias Klose Sat, 22 Aug 2015 15:10:19 +0200 + +yapps2 (2.1.1-17.2) unstable; urgency=low + + * Non-maintainer upload. + * Python 2.6 transition (closes: #547877): + + debian/control: + - Bump python-dev to >= 2.5.4-1~. + + debian/rules: + - Use macros provided by /usr/share/python/python.mk to install + files in correct locations for every supported Python version. + + -- Luca Falavigna Wed, 14 Oct 2009 23:05:28 +0200 + +yapps2 (2.1.1-17.1) unstable; urgency=low + + * Non-maintainer upload. + * Update package to the last python policy (Closes: 380992). + * Bump Standards-Version to 3.7.2. + * Move debhelper to Build-Depends. + + -- Pierre Habouzit Sun, 3 Sep 2006 23:51:24 +0200 + +yapps2 (2.1.1-17) unstable; urgency=medium + + * Fix recursive includes. + * Add option to limit backtrace depth on syntax errors. + + -- Matthias Urlichs Sat, 22 Jan 2005 04:10:33 +0100 + +yapps2 (2.1.1-16) unstable; urgency=medium + + * Brown paper bag -- fix Python 2.4 stuff. + + -- Matthias Urlichs Thu, 23 Dec 2004 23:48:58 +0100 + +yapps2 (2.1.1-15) unstable; urgency=medium + + * Add support for Python 2.4. + + -- Matthias Urlichs Sun, 12 Dec 2004 20:20:18 +0100 + +yapps2 (2.1.1-14) unstable; urgency=medium + + * Split off the Python parser runtime into its own package + + sort-of Closes: #272738: Generated python files import yapps.runtime + instead of yappsrt + - can't use yappsrt; it's not downward-compatible + * too many (i.e. more than zero) unquoted hyphens in the manpage + * update documentation that this is an enhanced version + + -- Matthias Urlichs Thu, 23 Sep 2004 10:44:41 +0200 + +yapps2 (2.1.1-13) unstable; urgency=low + + * latex2html => hevea + + -- Matthias Urlichs Mon, 19 Jul 2004 09:29:17 +0200 + +yapps2 (2.1.1-12) unstable; urgency=low + + * Build-Depend on python. + + -- Matthias Urlichs Mon, 12 Jul 2004 09:35:29 +0200 + +yapps2 (2.1.1-11) unstable; urgency=low + + * Typo (made large file handling slow) + * installation problem (new zero-sized file) + + -- Matthias Urlichs Sun, 16 May 2004 22:01:53 +0200 + +yapps2 (2.1.1-10) unstable; urgency=low + + * Documentation update: + build and install HTML documentation from LaTex source + + -- Matthias Urlichs Fri, 14 May 2004 12:14:33 +0200 + +yapps2 (2.1.1-9) unstable; urgency=low + + * Renamed the package to "yapps2". + * Submit to Debian. Closes: #201568. + * Fix minor problem with setup.py. + + -- Matthias Urlichs Fri, 14 May 2004 11:17:20 +0200 + +yapps (2.1.1-8) unstable; urgency=low + + * require python-dev because of distutils. + + -- Matthias Urlichs Wed, 31 Dec 2003 14:00:42 +0100 + +yapps (2.1.1-7) unstable; urgency=low + + * Change yapps.py to exit with 1 if there was a parser failure. + + -- Matthias Urlichs Wed, 31 Dec 2003 13:57:38 +0100 + +yapps (2.1.1-6) unstable; urgency=low + + * Update to 3.6.1, use build-depends-indep. + + -- Matthias Urlichs Tue, 30 Dec 2003 15:36:56 +0100 + +yapps (2.1.1-5) unstable; urgency=low + + * Add some notes. + + -- Matthias Urlichs Tue, 30 Dec 2003 15:33:19 +0100 + +yapps (2.1.1-4) unstable; urgency=low + + * Correctly report syntax errors if there are no line numbers. + + -- Matthias Urlichs Tue, 30 Dec 2003 15:30:05 +0100 + +yapps (2.1.1-3) unstable; urgency=low + + * Repair ignored-pattern upcall. + + -- Matthias Urlichs Tue, 30 Dec 2003 14:02:37 +0100 + +yapps (2.1.1-2) unstable; urgency=low + + * runtime: fix error reporting. + + -- Matthias Urlichs Tue, 30 Dec 2003 13:30:14 +0100 + +yapps (2.1.1-1) unstable; urgency=low + + * Initial Debian packaging. + - Added a manpage. + + -- Matthias Urlichs Mon, 29 Dec 2003 17:13:59 +0100 + --- yapps2-2.2.1.orig/debian/compat +++ yapps2-2.2.1/debian/compat @@ -0,0 +1 @@ +9 --- yapps2-2.2.1.orig/debian/control +++ yapps2-2.2.1/debian/control @@ -0,0 +1,59 @@ +Source: yapps2 +Section: python +Priority: optional +Maintainer: Matthias Urlichs +Build-Depends: debhelper (>= 9~) +Build-Depends-Indep: python-dev (>= 2.5.4-1~), python3-dev, + dh-python, + hevea, + python-setuptools, python3-setuptools, +Standards-Version: 3.9.8 + +Package: yapps2 +Architecture: all +Depends: ${python:Depends}, python3-yapps (= ${binary:Version}), ${misc:Depends}, + python3-pkg-resources, +Description: Yet Another Python Parser System + YAPPS is an easy to use parser generator that is written in Python and + generates Python code. There are several parser generator systems + already available for Python, but this parser has different goals: + Yapps is simple, very easy to use, and produces human-readable parsers. + . + It is not the fastest or most powerful parser. Yapps is designed to be + used when regular expressions are not enough and other parser systems + are too much: situations where you might otherwise write your own + recursive descent parser. + . + This package contains several upward-compatible enhancements to the + original YAPPS source: + . + - handles recursive input ("include files") + - better error reporting + - reads input incrementally + +Package: python-yapps +Architecture: all +Depends: ${python:Depends}, ${misc:Depends} +Replaces: yapps2-runtime +Conflicts: yapps2-runtime +Description: Yet Another Python Parser System + YAPPS is an easy to use parser generator that is written in Python and + generates Python code. There are several parser generator systems + already available for Python, but this parser has different goals: + Yapps is simple, very easy to use, and produces human-readable parsers. + . + This package contains the Python2 runtime support for parsers generated + with yapps2. + +Package: python3-yapps +Architecture: all +Depends: ${python3:Depends}, ${misc:Depends} +Description: Yet Another Python Parser System + YAPPS is an easy to use parser generator that is written in Python and + generates Python code. There are several parser generator systems + already available for Python, but this parser has different goals: + Yapps is simple, very easy to use, and produces human-readable parsers. + . + This package contains the Python3 runtime support for parsers generated + with yapps2. + --- yapps2-2.2.1.orig/debian/copyright +++ yapps2-2.2.1/debian/copyright @@ -0,0 +1,41 @@ +This is yapps2, Yet Another Python Parser System, +written by Amit J. Patel . + +It was packaged for Debian by Matthias Urlichs +on Fri, 14 May 2004. + +The original source can be found at: + http://theory.stanford.edu/~amitp/yapps/yapps2.1.1.zip + +The original copyright notice states: + +# Yapps 2 - yet another python parser system +# Copyright 1999-2003 by Amit J. Patel +# +# This version of Yapps 2 can be distributed under the +# terms of the MIT open source license, either found in the LICENSE file +# included with the Yapps distribution +# or at +# + +The LICENSE file states: + + + Permission is hereby granted, free of charge, to any person obtaining + a copy of this software and associated documentation files (the + "Software"), to deal in the Software without restriction, including + without limitation the rights to use, copy, modify, merge, publish, + distribute, sublicense, and/or sell copies of the Software, and to + permit persons to whom the Software is furnished to do so, subject to + the following conditions: + + The above copyright notice and this permission notice shall be included + in all copies or substantial portions of the Software. + + THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF + MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. + IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY + CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, + TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE + SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. --- yapps2-2.2.1.orig/debian/exporter +++ yapps2-2.2.1/debian/exporter @@ -0,0 +1,18 @@ +#!/bin/sh + +set -e + +test -n "$1" +test -z "$3" +if test -z "$2" ; then T="+"; else T="$2"; fi +D="$1" + +bk changes -v -r1.0..$T > "$D"/changelog +cd "$D" +if test ! -d doc ; then + mkdir doc yapps + mv yapps2.tex doc + mv yappsrt.py yapps/runtime.py + mv parsetree.py grammar.py yapps/ + rm yapps_grammar.py +fi --- yapps2-2.2.1.orig/debian/gbp.conf +++ yapps2-2.2.1/debian/gbp.conf @@ -0,0 +1,5 @@ +[buildpackage] +debian-branch=deb +upstream-branch=master +upstream-tree=BRANCH + --- yapps2-2.2.1.orig/debian/python-yapps.README +++ yapps2-2.2.1/debian/python-yapps.README @@ -0,0 +1,11 @@ +The Debian Package python-yapps2 +-------------------------------- + +This package contains the new runtime Python code for the augmented +yapps2 parser which is included in Debian. + +You need to depend on this package if you Debianize Python programs that +contain a yapps2-built parser. + +-- +Matthias Urlichs --- yapps2-2.2.1.orig/debian/python-yapps2.dirs +++ yapps2-2.2.1/debian/python-yapps2.dirs @@ -0,0 +1 @@ +usr/share/doc/python-yapps2 --- yapps2-2.2.1.orig/debian/python3-yapps.README +++ yapps2-2.2.1/debian/python3-yapps.README @@ -0,0 +1,11 @@ +The Debian Package python-yapps2 +-------------------------------- + +This package contains the new runtime Python code for the augmented +yapps2 parser which is included in Debian. + +You need to depend on this package if you Debianize Python3 programs that +contain a yapps2-built parser. + +-- +Matthias Urlichs --- yapps2-2.2.1.orig/debian/pyversions +++ yapps2-2.2.1/debian/pyversions @@ -0,0 +1 @@ +2.2- --- yapps2-2.2.1.orig/debian/rules +++ yapps2-2.2.1/debian/rules @@ -0,0 +1,21 @@ +#!/usr/bin/make -f + +export PYBUILD_NAME=yapps + +%: + dh $@ --with python2,python3 --buildsystem=pybuild + +override_dh_auto_build: + dh_auto_build + cd doc && hevea yapps2.tex + cd doc && hevea yapps2.tex # twice because of TOC + +override_dh_install: + mkdir -p debian/yapps2/usr/bin + mv debian/python3-yapps/usr/bin/yapps2 debian/yapps2/usr/bin + rm debian/python-yapps/usr/bin/yapps2 + dh_install + +override_dh_auto_test: + sh -x test.sh + --- yapps2-2.2.1.orig/debian/yapps.1 +++ yapps2-2.2.1/debian/yapps.1 @@ -0,0 +1,63 @@ +.\" $Revision: 1.5 $ +.TH YAPPS 1 +.SH NAME +yapps \- create a Python module from a grammar file +.SH SYNOPSIS +.B yapps +[ +.B \-\-dump +] +[ +.B \-\-use\-devel\-grammar +] +[ +.B \-fcontext\-insensitive\-scanner +] +[ +.BI \-p +.BI " pid" +] +[ +.BI \-f +] +input.g +[ +.BI output.py +] +.BI " name" +.SH DESCRIPTION + + \-\-dump Dump out grammar information + \-\-use\-devel\-grammar Use the devel grammar parser from + yapps_grammar.py instead of the stable grammar from grammar.py + \-fcontext\-insensitive\-scanner Scan all tokens (see docs) + +.I yapps +generates a Python program which will parse a given grammar. +.PP +.SH OPTIONS +.TP +.B \-\-dump +Dump the grammar information to stdout. +.TP +.B \-\-use\-devel\-grammar +Use the grammar file in ./yapps_grammar.py instead of yapps/grammar.py. +.br +This option is useful for testing new grammar parsers. (Yes, yapps' +parser is itself written with yapps...) +.TP +.B \-fcontext\-insensitive\-scanner +Set the option to use the non\-context\-sensitive scanner. +.SH CAVEATS +.I yapps +implements a recursive\-descent scanner. +.SH HISTORY +Written by Amit J. Patel . +.br +This version was enhanced by Matthias Urlichs . +It is +.B not +downwards-compatible with the original yapps2 (yet) and uses a different +runtime library. +.br +See the change log for details. --- yapps2-2.2.1.orig/debian/yapps2.dirs +++ yapps2-2.2.1/debian/yapps2.dirs @@ -0,0 +1,3 @@ +usr/bin +usr/share/doc/yapps2 +usr/share/doc/yapps2/html/ --- yapps2-2.2.1.orig/debian/yapps2.doc-base +++ yapps2-2.2.1/debian/yapps2.doc-base @@ -0,0 +1,10 @@ +Document: yapps2 +Title: Debian yapps Manual +Author: Amit J. Patel +Abstract: This manual describes the YAPPS parser generator. +Section: Programming/Python + +Format: HTML +Index: /usr/share/doc/yapps2/yapps2.html +Files: /usr/share/doc/yapps2/yapps2.html + --- yapps2-2.2.1.orig/debian/yapps2.docs +++ yapps2-2.2.1/debian/yapps2.docs @@ -0,0 +1,3 @@ +NOTES +doc/yapps2.tex +doc/yapps2.html --- yapps2-2.2.1.orig/debian/yapps2.manpages +++ yapps2-2.2.1/debian/yapps2.manpages @@ -0,0 +1 @@ +doc/yapps2.man --- yapps2-2.2.1.orig/doc/yapps2.haux +++ yapps2-2.2.1/doc/yapps2.haux @@ -0,0 +1,31 @@ +\@@addtocsec{htoc}{sec1}{0}{\@print{1}\quad{}Introduction{}} +\@@addtocsec{htoc}{sec2}{0}{\@print{2}\quad{}Examples{}} +\@@addtocsec{htoc}{sec3}{1}{\@print{2.1}\quad{}Introduction to Grammars{}} +\@@addtocsec{htoc}{sec4}{1}{\@print{2.2}\quad{}Lisp Expressions{}} +\@@addtocsec{htoc}{sec7}{1}{\@print{2.3}\quad{}Calculator{}} +\@@addtocsec{htoc}{sec8}{1}{\@print{2.4}\quad{}Calculator with Memory{}} +\@@addtocsec{htoc}{sec9}{0}{\@print{3}\quad{}Grammars{}} +\@@addtocsec{htoc}{sec10}{1}{\@print{3.1}\quad{}Left Factoring{}} +\newlabel{sec:Left-Factoring}{{3.1}{X}} +\@@addtocsec{htoc}{sec11}{1}{\@print{3.2}\quad{}Left Recursion{}} +\@@addtocsec{htoc}{sec12}{1}{\@print{3.3}\quad{}Ambiguous Grammars{}} +\newlabel{sec:Ambiguous-Grammars}{{3.3}{X}} +\@@addtocsec{htoc}{sec13}{0}{\@print{4}\quad{}Customization{}} +\@@addtocsec{htoc}{sec14}{1}{\@print{4.1}\quad{}Customizing Parsers{}} +\@@addtocsec{htoc}{sec15}{1}{\@print{4.2}\quad{}Customizing Scanners{}} +\@@addtocsec{htoc}{sec16}{0}{\@print{5}\quad{}Parser Mechanics{}} +\@@addtocsec{htoc}{sec17}{1}{\@print{5.1}\quad{}Parser Objects{}} +\newlabel{sec:Parser-Objects}{{5.1}{X}} +\@@addtocsec{htoc}{sec18}{1}{\@print{5.2}\quad{}Context Sensitive Scanner{}} +\@@addtocsec{htoc}{sec19}{1}{\@print{5.3}\quad{}Internal Variables{}} +\@@addtocsec{htoc}{sec20}{1}{\@print{5.4}\quad{}Pre- and Post-Parser Code{}} +\@@addtocsec{htoc}{sec21}{1}{\@print{5.5}\quad{}Representation of Grammars{}} +\@@addtocsec{htoc}{sec22}{0}{\@print{A}\quad{}Grammar for Parsers{}} +\@@addtocsec{htoc}{sec23}{0}{\@print{B}\quad{}Upgrading{}} +\@@addtocsec{htoc}{sec24}{0}{\@print{C}\quad{}Troubleshooting{}} +\@@addtocsec{htoc}{sec25}{0}{\@print{D}\quad{}History{}} +\@@addtocsec{htoc}{sec26}{0}{\@print{E}\quad{}Debian Extensions{}} +\newlabel{sec:debian}{{E}{X}} +\@@addtocsec{htoc}{sec27}{0}{\@print{F}\quad{}Future Extensions{}} +\newlabel{sec:future}{{F}{X}} +\@@addtocsec{htoc}{sec28}{0}{\@print{G}\quad{}References{}} --- yapps2-2.2.1.orig/doc/yapps2.html +++ yapps2-2.2.1/doc/yapps2.html @@ -0,0 +1,871 @@ + + + + + + +yapps2 + + + +
+ + + + + + +
The Yapps Parser Generator System
http://theory.stanford.edu/~amitp/Yapps/
Version 2
 
Amit J. Patel
http://www-cs-students.stanford.edu/ amitp/ +http://www-cs-students.stanford.edu/ amitp/
+
+ +

1  Introduction

Yapps (Yet Another Python +Parser System) is an easy to use parser +generator that is written in Python and generates Python code. There +are several parser generator systems already available for Python, +including PyLR, kjParsing, PyBison, and mcf.pars, +but I had different goals for my parser. Yapps is simple, is easy to +use, and produces human-readable parsers. It is not the fastest or +most powerful parser. Yapps is designed to be used when regular +expressions are not enough and other parser systems are too much: +situations where you may write your own recursive descent parser.

Some unusual features of Yapps that may be of interest are:

  1. Yapps produces recursive descent parsers that are readable by +humans, as opposed to table-driven parsers that are difficult to +read. A Yapps parser for a simple calculator looks similar to the +one that Mark Lutz wrote by hand for Programming Python.
  2. Yapps also allows for rules that accept parameters and pass +arguments to be used while parsing subexpressions. Grammars that +allow for arguments to be passed to subrules and for values to be +passed back are often called attribute grammars. In many +cases parameterized rules can be used to perform actions at “parse +time” that are usually delayed until later. For example, +information about variable declarations can be passed into the +rules that parse a procedure body, so that undefined variables can +be detected at parse time. The types of defined variables can be +used in parsing as well—for example, if the type of X is +known, we can determine whether X(1) is an array reference or +a function call.
  3. Yapps grammars are fairly easy to write, although there are +some inconveniences having to do with ELL(1) parsing that have to be +worked around. For example, rules have to be left factored and +rules may not be left recursive. However, neither limitation seems +to be a problem in practice.

    Yapps grammars look similar to the notation used in the Python +reference manual, with operators like *, +, |, +[], and () for patterns, names (tim) for rules, +regular expressions ("[a-z]+") for tokens, and # for +comments.

  4. The Yapps parser generator is written as a single Python module +with no C extensions. Yapps produces parsers that are written +entirely in Python, and require only the Yapps run-time module (5k) +for support.
  5. Yapps’s scanner is context-sensitive, picking tokens based on +the types of the tokens accepted by the parser. This can be +helpful when implementing certain kinds of parsers, such as for a +preprocessor.

There are several disadvantages of using Yapps over another parser system:

  1. Yapps parsers are ELL(1) (Extended LL(1)), which is +less powerful than LALR (used by PyLR) or +SLR (used by kjParsing), so Yapps would not be a +good choice for parsing complex languages. For example, allowing +both x := 5; and x; as statements is difficult +because we must distinguish based on only one token of lookahead. +Seeing only x, we cannot decide whether we have an +assignment statement or an expression statement. (Note however +that this kind of grammar can be matched with backtracking; see +section F.)
  2. The scanner that Yapps provides can only read from strings, not +files, so an entire file has to be read in before scanning can +begin. It is possible to build a custom scanner, though, so in +cases where stream input is needed (from the console, a network, or +a large file are examples), the Yapps parser can be given a custom +scanner that reads from a stream instead of a string.
  3. Yapps is not designed with efficiency in mind.

Yapps provides an easy to use parser generator that produces parsers +similar to what you might write by hand. It is not meant to be a +solution for all parsing problems, but instead an aid for those times +you would write a parser by hand rather than using one of the more +powerful parsing packages available.

Yapps 2.0 is easier to use than Yapps 1.0. New features include a +less restrictive input syntax, which allows mixing of sequences, +choices, terminals, and nonterminals; optional matching; the ability +to insert single-line statements into the generated parser; and +looping constructs * and + similar to the repetitive +matching constructs in regular expressions. Unfortunately, the +addition of these constructs has made Yapps 2.0 incompatible with +Yapps 1.0, so grammars will have to be rewritten. See section +?? for tips on changing Yapps 1.0 grammars for use +with Yapps 2.0.

+ +

2  Examples

In this section are several examples that show the use of Yapps. +First, an introduction shows how to construct grammars and write them +in Yapps form. This example can be skipped by someone familiar with +grammars and parsing. Next is a Lisp expression grammar that produces +a parse tree as output. This example demonstrates the use of tokens +and rules, as well as returning values from rules. The third example +is a expression evaluation grammar that evaluates during parsing +(instead of producing a parse tree).

+ +

2.1  Introduction to Grammars

A grammar for a natural language specifies how words can be put +together to form large structures, such as phrases and sentences. A +grammar for a computer language is similar in that it specifies how +small components (called tokens) can be put together to form +larger structures. In this section we will write a grammar for a tiny +subset of English.

Simple English sentences can be described as being a noun phrase +followed by a verb followed by a noun phrase. For example, in the +sentence, “Jack sank the blue ship,” the word “Jack” is the first +noun phrase, “sank” is the verb, and “the blue ship” is the second +noun phrase. In addition we should say what a noun phrase is; for +this example we shall say that a noun phrase is an optional article +(a, an, the) followed by any number of adjectives followed by a noun. +The tokens in our language are the articles, nouns, verbs, and +adjectives. The rules in our language will tell us how to +combine the tokens together to form lists of adjectives, noun phrases, +and sentences:

  • +sentence: noun_phrase verb noun_phrase +
  • noun_phrase: [article] adjective* noun +

Notice that some things that we said easily in English, such as +“optional article,” are expressed using special syntax, such as +brackets. When we said, “any number of adjectives,” we wrote +adjective*, where the * means “zero or more of the +preceding pattern”.

The grammar given above is close to a Yapps grammar. We also have to +specify what the tokens are, and what to do when a pattern is matched. +For this example, we will do nothing when patterns are matched; the +next example will explain how to perform match actions.

parser TinyEnglish:
+  ignore:          "\\W+"
+  token noun:      "(Jack|spam|ship)"
+  token verb:      "(sank|threw)"
+  token article:   "(an|a|the)"
+  token adjective: "(blue|red|green)"
+
+  rule sentence:       noun_phrase verb noun_phrase
+  rule noun_phrase:    [article] adjective* noun
+

The tokens are specified as Python regular expressions. Since +Yapps produces Python code, you can write any regular expression that +would be accepted by Python. (Note: These are Python 1.5 +regular expressions from the re module, not Python 1.4 +regular expressions from the regex module.) In addition to +tokens that you want to see (which are given names), you can also +specify tokens to ignore, marked by the ignore keyword. In +this parser we want to ignore whitespace.

The TinyEnglish grammar shows how you define tokens and rules, but it +does not specify what should happen once we’ve matched the rules. In +the next example, we will take a grammar and produce a parse +tree from it.

+ +

2.2  Lisp Expressions

Lisp syntax, although hated by many, has a redeeming quality: it is +simple to parse. In this section we will construct a Yapps grammar to +parse Lisp expressions and produce a parse tree as output.

+

Defining the Grammar

The syntax of Lisp is simple. It has expressions, which are +identifiers, strings, numbers, and lists. A list is a left +parenthesis followed by some number of expressions (separated by +spaces) followed by a right parenthesis. For example, 5, +"ni", and (print "1+2 = " (+ 1 2)) are Lisp expressions. +Written as a grammar,

    expr:   ID | STR | NUM | list
+    list:   ( expr* )  
+

In addition to having a grammar, we need to specify what to do every +time something is matched. For the tokens, which are strings, we just +want to get the “value” of the token, attach its type (identifier, +string, or number) in some way, and return it. For the lists, we want +to construct and return a Python list.

Once some pattern is matched, we enclose a return statement enclosed +in {{...}}. The braces allow us to insert any one-line +statement into the parser. Within this statement, we can refer to the +values returned by matching each part of the rule. After matching a +token such as ID, “ID” will be bound to the text of the +matched token. Let’s take a look at the rule:

    rule expr: ID   {{ return ('id', ID) }}
+      ...
+

In a rule, tokens return the text that was matched. For identifiers, +we just return the identifier, along with a “tag” telling us that +this is an identifier and not a string or some other value. Sometimes +we may need to convert this text to a different form. For example, if +a string is matched, we want to remove quotes and handle special forms +like \n. If a number is matched, we want to convert it into a +number. Let’s look at the return values for the other tokens:

      ...
+             | STR  {{ return ('str', eval(STR)) }}
+             | NUM  {{ return ('num', atoi(NUM)) }}
+      ...
+

If we get a string, we want to remove the quotes and process any +special backslash codes, so we run eval on the quoted string. +If we get a number, we convert it to an integer with atoi and +then return the number along with its type tag.

For matching a list, we need to do something slightly more +complicated. If we match a Lisp list of expressions, we want to +create a Python list with those values.

    rule list: "\\("                 # Match the opening parenthesis
+               {{ result = [] }}     # Create a Python list
+               ( 
+                  expr               # When we match an expression,
+                  {{ result.append(expr) }}   # add it to the list
+               )*                    # * means repeat this if needed
+               "\\)"                 # Match the closing parenthesis
+               {{ return result }}   # Return the Python list
+

In this rule we first match the opening parenthesis, then go into a +loop. In this loop we match expressions and add them to the list. +When there are no more expressions to match, we match the closing +parenthesis and return the resulting. Note that # is used for +comments, just as in Python.

The complete grammar is specified as follows: +

parser Lisp:
+    ignore:      '\\s+'
+    token NUM:   '[0-9]+'
+    token ID:    '[-+*/!@%^&=.a-zA-Z0-9_]+' 
+    token STR:   '"([^\\"]+|\\\\.)*"'
+
+    rule expr:   ID     {{ return ('id', ID) }}
+               | STR    {{ return ('str', eval(STR)) }}
+               | NUM    {{ return ('num', atoi(NUM)) }}
+               | list   {{ return list }}
+    rule list: "\\("    {{ result = [] }} 
+               ( expr   {{ result.append(expr) }}
+               )*  
+               "\\)"    {{ return result }} 
+

One thing you may have noticed is that "\\(" and "\\)" +appear in the list rule. These are inline tokens: +they appear in the rules without being given a name with the +token keyword. Inline tokens are more convenient to use, but +since they do not have a name, the text that is matched cannot be used +in the return value. They are best used for short simple patterns +(usually punctuation or keywords).

Another thing to notice is that the number and identifier tokens +overlap. For example, “487” matches both NUM and ID. In Yapps, the +scanner only tries to match tokens that are acceptable to the parser. +This rule doesn’t help here, since both NUM and ID can appear in the +same place in the grammar. There are two rules used to pick tokens if +more than one matches. One is that the longest match is +preferred. For example, “487x” will match as an ID (487x) rather +than as a NUM (487) followed by an ID (x). The second rule is that if +the two matches are the same length, the first one listed in +the grammar is preferred. For example, “487” will match as an NUM +rather than an ID because NUM is listed first in the grammar. Inline +tokens have preference over any tokens you have listed.

Now that our grammar is defined, we can run Yapps to produce a parser, +and then run the parser to produce a parse tree.

+

Running Yapps

In the Yapps module is a function generate that takes an +input filename and writes a parser to another file. We can use this +function to generate the Lisp parser, which is assumed to be in +lisp.g.

% python
+Python 1.5.1 (#1, Sep  3 1998, 22:51:17)  [GCC 2.7.2.3] on linux-i386
+Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
+>>> import yapps
+>>> yapps.generate('lisp.g')
+

At this point, Yapps has written a file lisp.py that contains +the parser. In that file are two classes (one scanner and one parser) +and a function (called parse) that puts things together for +you.

Alternatively, we can run Yapps from the command line to generate the +parser file:

% python yapps.py lisp.g
+

After running Yapps either from within Python or from the command +line, we can use the Lisp parser by calling the parse +function. The first parameter should be the rule we want to match, +and the second parameter should be the string to parse.

>>> import lisp
+>>> lisp.parse('expr', '(+ 3 4)')
+[('id', '+'), ('num', 3), ('num', 4)]
+>>> lisp.parse('expr', '(print "3 = " (+ 1 2))')
+[('id', 'print'), ('str', '3 = '), [('id', '+'), ('num', 1), ('num', 2)]]
+

The parse function is not the only way to use the parser; +section 5.1 describes how to access parser objects +directly.

We’ve now gone through the steps in creating a grammar, writing a +grammar file for Yapps, producing a parser, and using the parser. In +the next example we’ll see how rules can take parameters and also how +to do computations instead of just returning a parse tree.

+ +

2.3  Calculator

A common example parser given in many textbooks is that for simple +expressions, with numbers, addition, subtraction, multiplication, +division, and parenthesization of subexpressions. We’ll write this +example in Yapps, evaluating the expression as we parse.

Unlike yacc, Yapps does not have any way to specify +precedence rules, so we have to do it ourselves. We say that an +expression is the sum of terms, and that a term is the product of +factors, and that a factor is a number or a parenthesized expression:

    expr:           factor ( ("+"|"-") factor )*
+    factor:         term   ( ("*"|"/") term )*
+    term:           NUM | "(" expr ")"
+

In order to evaluate the expression as we go, we should keep along an +accumulator while evaluating the lists of terms or factors. Just as +we kept a “result” variable to build a parse tree for Lisp +expressions, we will use a variable to evaluate numerical +expressions. The full grammar is given below:

parser Calculator:
+    token END: "$"         # $ means end of string
+    token NUM: "[0-9]+"
+
+    rule goal:           expr END         {{ return expr }}
+
+    # An expression is the sum and difference of factors
+    rule expr:           factor           {{ v = factor }}
+                       ( "[+]" factor       {{ v = v+factor }}
+                       |  "-"  factor       {{ v = v-factor }}
+                       )*                 {{ return v }}
+
+    # A factor is the product and division of terms
+    rule factor:         term             {{ v = term }}
+                       ( "[*]" term         {{ v = v*term }}
+                       |  "/"  term         {{ v = v/term }}
+                       )*                 {{ return v }}
+
+    # A term is either a number or an expression surrounded by parentheses
+    rule term:           NUM              {{ return atoi(NUM) }}
+                       | "\\(" expr "\\)" {{ return expr }}
+

The top-level rule is goal, which says that we are looking for +an expression followed by the end of the string. The END +token is needed because without it, it isn’t clear when to stop +parsing. For example, the string “1+3” could be parsed either as +the expression “1” followed by the string “+3” or it could be +parsed as the expression “1+3”. By requiring expressions to end +with END, the parser is forced to take “1+3”.

In the two rules with repetition, the accumulator is named v. +After reading in one expression, we initialize the accumulator. Each +time through the loop, we modify the accumulator by adding, +subtracting, multiplying by, or dividing the previous accumulator by +the expression that has been parsed. At the end of the rule, we +return the accumulator.

The calculator example shows how to process lists of elements using +loops, as well as how to handle precedence of operators.

Note: It’s often important to put the END token in, so +put it in unless you are sure that your grammar has some other +non-ambiguous token marking the end of the program.

+ +

2.4  Calculator with Memory

In the previous example we learned how to write a calculator that +evaluates simple numerical expressions. In this section we will +extend the example to support both local and global variables.

To support global variables, we will add assignment statements to the +“goal” rule.

    rule goal:           expr END         {{ return expr }}
+              | 'set' ID expr END         {{ global_vars[ID] = expr }}
+                                          {{ return expr }}   
+

To use these variables, we need a new kind of terminal:

    rule term: ... | ID {{ return global_vars[ID] }} 
+

So far, these changes are straightforward. We simply have a global +dictionary global_vars that stores the variables and values, +we modify it when there is an assignment statement, and we look up +variables in it when we see a variable name.

To support local variables, we will add variable declarations to the +set of allowed expressions.

    rule term: ... | 'let' VAR '=' expr 'in' expr ...
+

This is where it becomes tricky. Local variables should be stored in +a local dictionary, not in the global one. One trick would be to save +a copy of the global dictionary, modify it, and then restore it +later. In this example we will instead use attributes to +create local information and pass it to subrules.

A rule can optionally take parameters. When we invoke the rule, we +must pass in arguments. For local variables, let’s use a single +parameter, local_vars:

    rule expr<<local_vars>>:   ...
+    rule factor<<local_vars>>: ...
+    rule term<<local_vars>>:   ...
+

Each time we want to match expr, factor, or +term, we will pass the local variables in the current rule to +the subrule. One interesting case is when we pass as an argument +something other than local_vars:

   rule term<<local_vars>>: ...
+                | 'let' VAR '=' expr<<local_vars>>
+                  {{ local_vars = [(VAR, expr)] + local_vars }}
+                  'in' expr<<local_vars>>
+                  {{ return expr }}
+

Note that the assignment to the local variables list does not modify +the original list. This is important to keep local variables from +being seen outside the “let”.

The other interesting case is when we find a variable:

global_vars = {}
+
+def lookup(map, name):
+    for x,v in map:  if x==name: return v
+    return global_vars[name]
+%%
+   ...
+   rule term<<local_vars>: ...
+                | VAR {{ return lookup(local_vars, VAR) }}
+

The lookup function will search through the local variable list, and +if it cannot find the name there, it will look it up in the global +variable dictionary.

A complete grammar for this example, including a read-eval-print loop +for interacting with the calculator, can be found in the examples +subdirectory included with Yapps.

In this section we saw how to insert code before the parser. We also +saw how to use attributes to transmit local information from one rule +to its subrules.

+ +

3  Grammars

Each Yapps grammar has a name, a list of tokens, and a set of +production rules. A grammar named X will be used to produce +a parser named X and a scanner anmed XScanner. As +in Python, names are case sensitive, start with a letter, and contain +letters, numbers, and underscores (_).

There are three kinds of tokens in Yapps: named, inline, and ignored. +As their name implies, named tokens are given a name, using the token +construct: token name : regexp. In a rule, the +token can be matched by using the name. Inline tokens are regular +expressions that are used in rules without being declared. Ignored +tokens are declared using the ignore construct: ignore: +regexp. These tokens are ignored by the scanner, and are +not seen by the parser. Often whitespace is an ignored token. The +regular expressions used to define tokens should use the syntax +defined in the re module, so some symbols may have to be +backslashed.

Production rules in Yapps have a name and a pattern to match. If the +rule is parameterized, the name should be followed by a list of +parameter names in <<...>>. A pattern can be a simple pattern +or a compound pattern. Simple patterns are the name of a named token, +a regular expression in quotes (inline token), the name of a +production rule (followed by arguments in <<...>>, if the rule +has parameters), and single line Python statements ({{...}}). +Compound patterns are sequences (A B C ...), choices ( +A | B | C | ...), options ([...]), zero-or-more repetitions +(...*), and one-or-more repetitions (...+). Like +regular expressions, repetition operators have a higher precedence +than sequences, and sequences have a higher precedence than choices.

Whenever {{...}} is used, a legal one-line Python statement +should be put inside the braces. The token }} should not +appear within the {{...}} section, even within a string, since +Yapps does not attempt to parse the Python statement. A workaround +for strings is to put two strings together ("}" "}"), or to use +backslashes ("}\}"). At the end of a rule you should use a +{{ return X }} statement to return a value. However, you +should not use any control statements (return, +continue, break) in the middle of a rule. Yapps +needs to make assumptions about the control flow to generate a parser, +and any changes to the control flow will confuse Yapps.

The <<...>> form can occur in two places: to define parameters +to a rule and to give arguments when matching a rule. Parameters use +the syntax used for Python functions, so they can include default +arguments and the special forms (*args and **kwargs). +Arguments use the syntax for Python function call arguments, so they +can include normal arguments and keyword arguments. The token +>> should not appear within the <<...>> section.

In both the statements and rule arguments, you can use names defined +by the parser to refer to matched patterns. You can refer to the text +matched by a named token by using the token name. You can use the +value returned by a production rule by using the name of that rule. +If a name X is matched more than once (such as in loops), you +will have to save the earlier value(s) in a temporary variable, and +then use that temporary variable in the return value. The next +section has an example of a name that occurs more than once.

+ +

3.1  Left Factoring

+

Yapps produces ELL(1) parsers, which determine which clause to match +based on the first token available. Sometimes the leftmost tokens of +several clauses may be the same. The classic example is the +if/then/else construct in Pascal:

rule stmt:  "if" expr "then" stmt {{ then_part = stmt }} 
+                      "else" stmt {{ return ('If',expr,then_part,stmt) }}
+          | "if" expr "then" stmt {{ return ('If',expr,stmt,[]) }}
+

(Note that we have to save the first stmt into a variable +because there is another stmt that will be matched.) The +left portions of the two clauses are the same, which presents a +problem for the parser. The solution is left-factoring: the +common parts are put together, and then a choice is made about +the remaining part:

rule stmt:  "if" expr 
+              "then" stmt {{ then_part = stmt }}
+              {{ else_part = [] }}
+              [ "else" stmt {{ else_part = stmt }} ]
+            {{ return ('If', expr, then_part, else_part) }}
+

Unfortunately, the classic if/then/else situation is +still ambiguous when you left-factor. Yapps can deal with this +situation, but will report a warning; see section +3.3 for details.

In general, replace rules of the form:

rule A:   a b1 {{ return E1 }}
+        | a b2 {{ return E2 }}
+        | c3   {{ return E3 }}
+        | c4   {{ return E4 }}
+

with rules of the form:

rule A:   a ( b1 {{ return E1 }}
+            | b2 {{ return E2 }}
+            )
+        | c3   {{ return E3 }}
+        | c4   {{ return E4 }}
+
+ +

3.2  Left Recursion

A common construct in grammars is for matching a list of patterns, +sometimes separated with delimiters such as commas or semicolons. In +LR-based parser systems, we can parse a list with something like this:

rule sum:  NUM             {{ return NUM }}
+         | sum "+" NUM     {{ return (sum, NUM) }}
+

Parsing 1+2+3+4 would produce the output +(((1,2),3),4), which is what we want from a left-associative +addition operator. Unfortunately, this grammar is left +recursive, because the sum rule contains a clause that +begins with sum. (The recursion occurs at the left side of +the clause.)

We must restructure this grammar to be right recursive instead:

rule sum:  NUM             {{ return NUM }}
+         | NUM "+" sum     {{ return (NUM, sum) }}
+

Unfortunately, using this grammar, 1+2+3+4 would be parsed as +(1,(2,(3,4))), which no longer follows left associativity. +The rule also needs to be left-factored. Instead, we write the +pattern as a loop instead:

rule sum:       NUM {{ v = NUM }}
+                ( "[+]" NUM {{ v = (v,NUM) }} )*
+                {{ return v }}
+

In general, replace rules of the form:

rule A:  A a1 -> << E1 >> 
+       | A a2 -> << E2 >>
+       | b3   -> << E3 >>
+       | b4   -> << E4 >>
+

with rules of the form:

rule A:  ( b3 {{ A = E3 }} 
+         | b4 {{ A = E4 }} )
+         ( a1 {{ A = E1 }}
+         | a2 {{ A = E2 }} )*
+         {{ return A }}
+

We have taken a rule that proved problematic for with recursion and +turned it into a rule that works well with looping constructs.

+ +

3.3  Ambiguous Grammars

+

In section 3.1 we saw the classic if/then/else +ambiguity, which occurs because the “else …” portion of an “if +…then …else …” construct is optional. Programs with +nested if/then/else constructs can be ambiguous when one of the else +clauses is missing: +

if 1 then            if 1 then
+    if 5 then            if 5 then
+        x := 1;              x := 1;
+    else             else
+        y := 9;          y := 9;
+

The indentation shows that the program can be parsed in two different +ways. (Of course, if we all would adopt Python’s indentation-based +structuring, this would never happen!) Usually we want the parsing on +the left: the “else” should be associated with the closest “if” +statement. In section 3.1 we “solved” the +problem by using the following grammar:

rule stmt:  "if" expr 
+              "then" stmt {{ then_part = stmt }}
+              {{ else_part = [] }}
+              [ "else" stmt {{ else_part = stmt }} ]
+            {{ return ('If', expr, then_part, else_part) }}
+

Here, we have an optional match of “else” followed by a statement. +The ambiguity is that if an “else” is present, it is not clear +whether you want it parsed immediately or if you want it to be parsed +by the outer “if”.

Yapps will deal with the situation by matching when the else pattern +when it can. The parser will work in this case because it prefers the +first matching clause, which tells Yapps to parse the “else”. +That is exactly what we want!

For ambiguity cases with choices, Yapps will choose the first +matching choice. However, remember that Yapps only looks at the first +token to determine its decision, so (a b | a c) will result in +Yapps choosing a b even when the input is a c. It only +looks at the first token, a, to make its decision.

+ +

4  Customization

Both the parsers and the scanners can be customized. The parser is +usually extended by subclassing, and the scanner can either be +subclassed or completely replaced.

+ +

4.1  Customizing Parsers

If additional fields and methods are needed in order for a parser to +work, Python subclassing can be used. (This is unlike parser classes +written in static languages, in which these fields and methods must be +defined in the generated parser class.) We simply subclass the +generated parser, and add any fields or methods required. Expressions +in the grammar can call methods of the subclass to perform any actions +that cannot be expressed as a simple expression. For example, +consider this simple grammar:

parser X:
+    rule goal:  "something"  {{ self.printmsg() }}
+

The printmsg function need not be implemented in the parser +class X; it can be implemented in a subclass:

import Xparser
+
+class MyX(Xparser.X):
+    def printmsg(self):
+        print "Hello!"
+
+ +

4.2  Customizing Scanners

The generated parser class is not dependent on the generated scanner +class. A scanner object is passed to the parser object’s constructor +in the parse function. To use a different scanner, write +your own function to construct parser objects, with an instance of a +different scanner. Scanner objects must have a token method +that accepts an integer N as well as a list of allowed token +types, and returns the Nth token, as a tuple. The default scanner +raises NoMoreTokens if no tokens are available, and +SyntaxError if no token could be matched. However, the +parser does not rely on these exceptions; only the parse +convenience function (which calls wrap_error_reporter) and +the print_error error display function use those exceptions.

The tuples representing tokens have four elements. The first two are +the beginning and ending indices of the matched text in the input +string. The third element is the type tag, matching either the name +of a named token or the quoted regexp of an inline or ignored token. +The fourth element of the token tuple is the matched text. If the +input string is s, and the token tuple is +(b,e,type,val), then val should be equal to +s[b:e].

The generated parsers do not the beginning or ending index. They use +only the token type and value. However, the default error reporter +uses the beginning and ending index to show the user where the error +is.

+ +

5  Parser Mechanics

The base parser class (Parser) defines two methods, _scan +and _peek, and two fields, _pos and +_scanner. The generated parser inherits from the base +parser, and contains one method for each rule in the grammar. To +avoid name clashes, do not use names that begin with an underscore +(_).

+ +

5.1  Parser Objects

+

Yapps produces as output two exception classes, a scanner class, a +parser class, and a function parse that puts everything +together. The parse function does not have to be used; +instead, one can create a parser and scanner object and use them +together for parsing.

    def parse(rule, text):
+        P = X(XScanner(text))
+        return wrap_error_reporter(P, rule)
+

The parse function takes a name of a rule and an input string +as input. It creates a scanner and parser object, then calls +wrap_error_reporter to execute the method in the parser +object named rule. The wrapper function will call the +appropriate parser rule and report any parsing errors to standard +output.

There are several situations in which the parse function +would not be useful. If a different parser or scanner is being used, +or exceptions are to be handled differently, a new parse +function would be required. The supplied parse function can +be used as a template for writing a function for your own needs. An +example of a custom parse function is the generate function +in Yapps.py.

+ +

5.2  Context Sensitive Scanner

Unlike most scanners, the scanner produced by Yapps can take into +account the context in which tokens are needed, and try to match only +good tokens. For example, in the grammar:

parser IniFile:
+   token ID:   "[a-zA-Z_0-9]+"
+   token VAL:  ".*"
+
+   rule pair:  ID "[ \t]*=[ \t]*" VAL "\n"
+

we would like to scan lines of text and pick out a name/value pair. +In a conventional scanner, the input string shell=progman.exe +would be turned into a single token of type VAL. The Yapps +scanner, however, knows that at the beginning of the line, an +ID is expected, so it will return "shell" as a token +of type ID. Later, it will return "progman.exe" as +a token of type VAL.

Context sensitivity decreases the separation between scanner and +parser, but it is useful in parsers like IniFile, where the +tokens themselves are not unambiguous, but are unambiguous +given a particular stage in the parsing process.

Unfortunately, context sensitivity can make it more difficult to +detect errors in the input. For example, in parsing a Pascal-like +language with “begin” and “end” as keywords, a context sensitive +scanner would only match “end” as the END token if the parser is in +a place that will accept the END token. If not, then the scanner +would match “end” as an identifier. To disable the context +sensitive scanner in Yapps, add the +context-insensitive-scanner option to the grammar:

Parser X:
+    option:  "context-insensitive-scanner"
+

Context-insensitive scanning makes the parser look cleaner as well.

+ +

5.3  Internal Variables

There are two internal fields that may be of use. The parser object +has two fields, _pos, which is the index of the current +token being matched, and _scanner, which is the scanner +object. The token itself can be retrieved by accessing the scanner +object and calling the token method with the token index. However, if you call token before the token has been requested by the parser, it may mess up a context-sensitive scanner.1 A +potentially useful combination of these fields is to extract the +portion of the input matched by the current rule. To do this, just save the scanner state (_scanner.pos) before the text is matched and then again after the text is matched:

  rule R: 
+      {{ start = self._scanner.pos }}
+      a b c 
+      {{ end = self._scanner.pos }}
+      {{ print 'Text is', self._scanner.input[start:end] }}
+
+ +

5.4  Pre- and Post-Parser Code

Sometimes the parser code needs to rely on helper variables, +functions, and classes. A Yapps grammar can optionally be surrounded +by double percent signs, to separate the grammar from Python code.

... Python code ...
+%%
+... Yapps grammar ...
+%%
+... Python code ...
+

The second %% can be omitted if there is no Python code at the +end, and the first %% can be omitted if there is no extra +Python code at all. (To have code only at the end, both separators +are required.)

If the second %% is omitted, Yapps will insert testing code +that allows you to use the generated parser to parse a file.

The extended calculator example in the Yapps examples subdirectory +includes both pre-parser and post-parser code.

+ +

5.5  Representation of Grammars

For each kind of pattern there is a class derived from Pattern. Yapps +has classes for Terminal, NonTerminal, Sequence, Choice, Option, Plus, +Star, and Eval. Each of these classes has the following interface:

  • +setup(gen) Set accepts-є, and call +gen.changed() if it changed. This function can change the +flag from false to true but not from true to false. +
  • update((gen)) Set firstand follow, and call +gen.changed() if either changed. This function can add to +the sets but not remove from them. +
  • output(gen, indent) Generate code for matching +this rule, using indent as the current indentation level. +Writes are performed using gen.write. +
  • used(vars) Given a list of variables vars, +return two lists: one containing the variables that are used, and +one containing the variables that are assigned. This function is +used for optimizing the resulting code. +

Both setup and update monotonically increase the +variables they modify. Since the variables can only increase a finite +number of times, we can repeatedly call the function until the +variable stabilized. The used function is not currently +implemented.

With each pattern in the grammar Yapps associates three pieces of +information: the firstset, the followset, and the +accepts-є flag.

The firstset contains the tokens that can appear as we start +matching the pattern. The followset contains the tokens that can +appear immediately after we match the pattern. The accepts-є +flag is true if the pattern can match no tokens. In this case, firstwill contain all the elements in follow. The followset is not +needed when accepts-є is false, and may not be accurate in +those cases.

Yapps does not compute these sets precisely. Its approximation can +miss certain cases, such as this one:

  rule C: ( A* | B )
+  rule B: C [A]
+

Yapps will calculate C’s followset to include A. +However, C will always match all the A’s, so A will +never follow it. Yapps 2.0 does not properly handle this construct, +but if it seems important, I may add support for it in a future +version.

Yapps also cannot handle constructs that depend on the calling +sequence. For example:

  rule R: U | 'b'
+  rule S:   | 'c'
+  rule T: S 'b'
+  rule U: S 'a'
+

The followset for S includes a and b. Since S can be empty, the firstset for S should include a, +b, and c. However, when parsing R, if the lookahead +is b we should not parse U. That’s because in U, S is followed by a and not b. Therefore in +R, we should choose rule U only if there is an a or +c, but not if there is a b. Yapps and many other LL(1) +systems do not distinguish S b and S a, making S’s followset a, b, and making R always try to match +U. In this case we can solve the problem by changing R to +'b' | U but it may not always be possible to solve all such +problems in this way.

+ +

A  Grammar for Parsers

This is the grammar for parsers, without any Python code mixed in. +The complete grammar can be found in parsedesc.g in the Yapps +distribution.

parser ParserDescription:
+    ignore:      "\\s+"
+    ignore:      "#.*?\r?\n"
+    token END:   "$"  # $ means end of string
+    token ATTR:  "<<.+?>>"
+    token STMT:  "{{.+?}}"
+    token ID:    '[a-zA-Z_][a-zA-Z_0-9]*'
+    token STR:   '[rR]?\'([^\\n\'\\\\]|\\\\.)*\'|[rR]?"([^\\n"\\\\]|\\\\.)*"'
+
+    rule Parser: "parser" ID ":"
+                   Options
+                   Tokens
+                   Rules
+                 END 
+
+    rule Options:  ( "option" ":" STR )*
+    rule Tokens:   ( "token" ID ":" STR | "ignore"   ":" STR )*
+    rule Rules:    ( "rule" ID OptParam ":" ClauseA )*
+
+    rule ClauseA:  ClauseB ( '[|]' ClauseB )*
+    rule ClauseB:  ClauseC*
+    rule ClauseC:  ClauseD [ '[+]' | '[*]' ]
+    rule ClauseD:  STR | ID [ATTR] | STMT
+                 | '\\(' ClauseA '\\) | '\\[' ClauseA '\\]'
+
+ +

B  Upgrading

Yapps 2.0 is not backwards compatible with Yapps 1.0. In this section +are some tips for upgrading:

  1. +Yapps 1.0 was distributed as a single file. Yapps 2.0 is +instead distributed as two Python files: a parser generator +(26k) and a parser runtime (5k). You need both files to +create parsers, but you need only the runtime (yappsrt.py) +to use the parsers.
  2. Yapps 1.0 supported Python 1.4 regular expressions from the +regex module. Yapps 2.0 uses Python 1.5 regular +expressions from the re module. The new syntax for +regular expressions is not compatible with the old syntax. +Andrew Kuchling has a guide to converting +regular +expressionshttp://www.python.org/doc/howto/regex-to-re/ on his +web page.
  3. Yapps 1.0 wants a pattern and then a return value in -> +<<...>>. Yapps 2.0 allows patterns and Python statements to +be mixed. To convert a rule like this:
    rule R: A B C -> << E1 >>
+      | X Y Z -> << E2 >>
+

    to Yapps 2.0 form, replace the return value specifiers with return +statements:

    rule R: A B C {{ return E1 }}
+      | X Y Z {{ return E2 }}
+
  4. Yapps 2.0 does not perform tail recursion elimination. This +means any recursive rules you write will be turned into recursive +methods in the parser. The parser will work, but may be slower. +It can be made faster by rewriting recursive rules, using instead +the looping operators * and + provided in Yapps 2.0.
+ +

C  Troubleshooting

  • +A common error is to write a grammar that doesn’t have an END +token. End tokens are needed when it is not clear when to stop +parsing. For example, when parsing the expression 3+5, it is +not clear after reading 3 whether to treat it as a complete +expression or whether the parser should continue reading. +Therefore the grammar for numeric expressions should include an end +token. Another example is the grammar for Lisp expressions. In +Lisp, it is always clear when you should stop parsing, so you do +not need an end token. In fact, it may be more useful not +to have an end token, so that you can read in several Lisp expressions. +
  • If there is a chance of ambiguity, make sure to put the choices +in the order you want them checked. Usually the most specific +choice should be first. Empty sequences should usually be last. +
  • The context sensitive scanner is not appropriate for all +grammars. You might try using the insensitive scanner with the +context-insensitive-scanner option in the grammar. +
  • If performance turns out to be a problem, try writing a custom +scanner. The Yapps scanner is rather slow (but flexible and easy +to understand). +
+ +

D  History

Yapps 1 had several limitations that bothered me while writing +parsers:

  1. +It was not possible to insert statements into the generated +parser. A common workaround was to write an auxilliary function +that executed those statements, and to call that function as part +of the return value calculation. For example, several of my +parsers had an “append(x,y)” function that existed solely to call +“x.append(y)”. +
  2. The way in which grammars were specified was rather +restrictive: a rule was a choice of clauses. Each clause was a +sequence of tokens and rule names, followed by a return value. +
  3. Optional matching had to be put into a separate rule because +choices were only made at the beginning of a rule. +
  4. Repetition had to be specified in terms of recursion. Not only +was this awkward (sometimes requiring additional rules), I had to +add a tail recursion optimization to Yapps to transform the +recursion back into a loop. +

Yapps 2 addresses each of these limitations.

  1. +Statements can occur anywhere within a rule. (However, only +one-line statements are allowed; multiline blocks marked by +indentation are not.) +
  2. Grammars can be specified using any mix of sequences, choices, +tokens, and rule names. To allow for complex structures, +parentheses can be used for grouping. +
  3. Given choices and parenthesization, optional matching can be +expressed as a choice between some pattern and nothing. In +addition, Yapps 2 has the convenience syntax [A B ...] for +matching A B ... optionally. +
  4. Repetition operators * for zero or more and + for +one or more make it easy to specify repeating patterns. +

It is my hope that Yapps 2 will be flexible enough to meet my needs +for another year, yet simple enough that I do not hesitate to use it.

+ +

E  Debian Extensions

+

The Debian version adds the following enhancements to the original +Yapps code. They were written by Matthias Urlichs.

  1. +Yapps can stack input sources ("include files"). A usage example +is supplied with the calc.g sample program. +
  2. Yapps now understands augmented ignore-able patterns. +This means that Yapps can parse multi-line C comments; this wasn’t +possible before. +
  3. Better error reporting. +
  4. Yapps now reads its input incrementally. +

The generated parser has been renamed to yapps/runtime.py. +In Debian, this file is provided by the yapps2-runtime package. +You need to depend on it if you Debianize Python programs which use +yapps.

+ +

F  Future Extensions

+

I am still investigating the possibility of LL(2) and higher +lookahead. However, it looks like the resulting parsers will be +somewhat ugly.

It would be nice to control choices with user-defined predicates.

The most likely future extension is backtracking. A grammar pattern +like (VAR ':=' expr)? {{ return Assign(VAR,expr) }} : expr {{ return expr }} +would turn into code that attempted to match VAR ':=' expr. If +it succeeded, it would run {{ return ... }}. If it failed, it +would match expr {{ return expr }}. Backtracking may make it +less necessary to write LL(2) grammars.

+ +

G  References

  1. +The Python-Parser +SIGhttp://www.python.org/sigs/parser-sig/ is the first place +to look for a list of parser systems for Python.
  2. ANTLR/PCCTS, by Terrence Parr, is available at +The ANTLR Home Pagehttp://www.antlr.org/.
  3. PyLR, by Scott Cotton, is at his Starship +pagehttp://starship.skyport.net/crew/scott/PyLR.html.
  4. John Aycock’s Compiling Little Languages +Frameworkhttp://www.foretec.com/python/workshops/1998-11/proceedings/papers/aycock-little/aycock-little.html.
  5. PyBison, by Scott Hassan, can be found at +his Python Projects +pagehttp://coho.stanford.edu/~hassan/Python/.
  6. mcf.pars, by Mike C. Fletcher, is available at +his web +pagehttp://members.rogers.com/mcfletch/programming/simpleparse/simpleparse.html.
  7. kwParsing, by Aaron Watters, is available at +his Starship +pagehttp://starship.skyport.net/crew/aaron_watters/kwParsing/. +
+
+1
When using a context-sensitive scanner, the parser tells the scanner what the valid token types are at each point. If you call token before the parser can tell the scanner the valid token types, the scanner will attempt to match without considering the context.
+ + + + + +
This document was translated from LATEX by +HEVEA.
+ --- yapps2-2.2.1.orig/doc/yapps2.htoc +++ yapps2-2.2.1/doc/yapps2.htoc @@ -0,0 +1,36 @@ +\begin{tocenv} +\tocitem \@locref{sec1}{\begin{@norefs}\@print{1}\quad{}Introduction{}\end{@norefs}} +\tocitem \@locref{sec2}{\begin{@norefs}\@print{2}\quad{}Examples{}\end{@norefs}} +\begin{tocenv} +\tocitem \@locref{sec3}{\begin{@norefs}\@print{2.1}\quad{}Introduction to Grammars{}\end{@norefs}} +\tocitem \@locref{sec4}{\begin{@norefs}\@print{2.2}\quad{}Lisp Expressions{}\end{@norefs}} +\tocitem \@locref{sec7}{\begin{@norefs}\@print{2.3}\quad{}Calculator{}\end{@norefs}} +\tocitem \@locref{sec8}{\begin{@norefs}\@print{2.4}\quad{}Calculator with Memory{}\end{@norefs}} +\end{tocenv} +\tocitem \@locref{sec9}{\begin{@norefs}\@print{3}\quad{}Grammars{}\end{@norefs}} +\begin{tocenv} +\tocitem \@locref{sec10}{\begin{@norefs}\@print{3.1}\quad{}Left Factoring{}\end{@norefs}} +\tocitem \@locref{sec11}{\begin{@norefs}\@print{3.2}\quad{}Left Recursion{}\end{@norefs}} +\tocitem \@locref{sec12}{\begin{@norefs}\@print{3.3}\quad{}Ambiguous Grammars{}\end{@norefs}} +\end{tocenv} +\tocitem \@locref{sec13}{\begin{@norefs}\@print{4}\quad{}Customization{}\end{@norefs}} +\begin{tocenv} +\tocitem \@locref{sec14}{\begin{@norefs}\@print{4.1}\quad{}Customizing Parsers{}\end{@norefs}} +\tocitem \@locref{sec15}{\begin{@norefs}\@print{4.2}\quad{}Customizing Scanners{}\end{@norefs}} +\end{tocenv} +\tocitem \@locref{sec16}{\begin{@norefs}\@print{5}\quad{}Parser Mechanics{}\end{@norefs}} +\begin{tocenv} +\tocitem \@locref{sec17}{\begin{@norefs}\@print{5.1}\quad{}Parser Objects{}\end{@norefs}} +\tocitem \@locref{sec18}{\begin{@norefs}\@print{5.2}\quad{}Context Sensitive Scanner{}\end{@norefs}} +\tocitem \@locref{sec19}{\begin{@norefs}\@print{5.3}\quad{}Internal Variables{}\end{@norefs}} +\tocitem \@locref{sec20}{\begin{@norefs}\@print{5.4}\quad{}Pre- and Post-Parser Code{}\end{@norefs}} +\tocitem \@locref{sec21}{\begin{@norefs}\@print{5.5}\quad{}Representation of Grammars{}\end{@norefs}} +\end{tocenv} +\tocitem \@locref{sec22}{\begin{@norefs}\@print{A}\quad{}Grammar for Parsers{}\end{@norefs}} +\tocitem \@locref{sec23}{\begin{@norefs}\@print{B}\quad{}Upgrading{}\end{@norefs}} +\tocitem \@locref{sec24}{\begin{@norefs}\@print{C}\quad{}Troubleshooting{}\end{@norefs}} +\tocitem \@locref{sec25}{\begin{@norefs}\@print{D}\quad{}History{}\end{@norefs}} +\tocitem \@locref{sec26}{\begin{@norefs}\@print{E}\quad{}Debian Extensions{}\end{@norefs}} +\tocitem \@locref{sec27}{\begin{@norefs}\@print{F}\quad{}Future Extensions{}\end{@norefs}} +\tocitem \@locref{sec28}{\begin{@norefs}\@print{G}\quad{}References{}\end{@norefs}} +\end{tocenv} --- yapps2-2.2.1.orig/setup.py +++ yapps2-2.2.1/setup.py @@ -1,13 +1,13 @@ #!/usr/bin/env python -from setuptools import setup, find_packages +from setuptools import setup import os from yapps import __version__ as version pkg_root = os.path.dirname(__file__) # Error-handling here is to allow package to be built w/o README included -try: readme = open(os.path.join(pkg_root, 'README.txt')).read() +try: readme = open(os.path.join(pkg_root, 'README.md')).read() except IOError: readme = '' setup( @@ -15,15 +15,15 @@ version = version, author = 'Amit J. Patel, Matthias Urlichs', author_email = 'amitp@cs.stanford.edu, smurf@debian.org', - maintainer = 'Mike Kazantsev', - maintainer_email = 'mk.fraggod@gmail.com', + maintainer = 'Matthias Urlichs', + maintainer_email = 'smurf@debian.org', license = 'MIT', - url = 'https://github.com/mk-fg/yapps', + url = 'https://github.com/smurfix/yapps', description = 'Yet Another Python Parser System', long_description = readme, - packages = find_packages(), + packages = ['yapps'], include_package_data = True, package_data = {'': ['README.txt']}, exclude_package_data = {'': ['README.*']}, --- yapps2-2.2.1.orig/yapps/cli_tool.py +++ yapps2-2.2.1/yapps/cli_tool.py @@ -1,4 +1,4 @@ -#!/usr/bin/env python +#!/usr/bin/python3 # # Yapps 2 - yet another python parser system