2012-12-13 04:44:07 +00:00
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\input texinfo @c -*-texinfo-*-
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@c %**start of header
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2014-06-10 02:20:31 +00:00
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@setfilename ../../info/wisent.info
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2012-12-13 04:44:07 +00:00
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@set TITLE Wisent Parser Development
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@set AUTHOR Eric M. Ludlam, David Ponce, and Richard Y. Kim
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@settitle @value{TITLE}
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Fix single-quoting style in PDF manuals
The PDF versions of the GNU manuals used curved single quotes to
represent grave accent and apostrophe, which made it a pain to cut
and paste code examples from them. Fix the PDF versions to use
grave accent and apostrophe for Lisp source code, keystrokes, etc.
This change does not affect the info files, nor does it affect
ordinary uses of curved single quotes in PDF.
* doc/emacs/docstyle.texi: New file, which specifies treatment for
grave accent and apostrophe, as well as the document encoding.
* doc/emacs/emacs-xtra.texi, doc/emacs/emacs.texi:
* doc/lispintro/emacs-lisp-intro.texi:
* doc/lispref/back.texi, doc/lispref/book-spine.texi:
* doc/lispref/elisp.texi, doc/lispref/lay-flat.texi:
* doc/misc/ada-mode.texi, doc/misc/auth.texi:
* doc/misc/autotype.texi, doc/misc/bovine.texi, doc/misc/calc.texi:
* doc/misc/cc-mode.texi, doc/misc/cl.texi, doc/misc/dbus.texi:
* doc/misc/dired-x.texi, doc/misc/ebrowse.texi, doc/misc/ede.texi:
* doc/misc/ediff.texi, doc/misc/edt.texi, doc/misc/efaq-w32.texi:
* doc/misc/efaq.texi, doc/misc/eieio.texi, doc/misc/emacs-gnutls.texi:
* doc/misc/emacs-mime.texi, doc/misc/epa.texi, doc/misc/erc.texi:
* doc/misc/ert.texi, doc/misc/eshell.texi, doc/misc/eudc.texi:
* doc/misc/eww.texi, doc/misc/flymake.texi, doc/misc/forms.texi:
* doc/misc/gnus-coding.texi, doc/misc/gnus-faq.texi:
* doc/misc/gnus.texi, doc/misc/htmlfontify.texi:
* doc/misc/idlwave.texi, doc/misc/ido.texi, doc/misc/info.texi:
* doc/misc/mairix-el.texi, doc/misc/message.texi, doc/misc/mh-e.texi:
* doc/misc/newsticker.texi, doc/misc/nxml-mode.texi:
* doc/misc/octave-mode.texi, doc/misc/org.texi, doc/misc/pcl-cvs.texi:
* doc/misc/pgg.texi, doc/misc/rcirc.texi, doc/misc/reftex.texi:
* doc/misc/remember.texi, doc/misc/sasl.texi, doc/misc/sc.texi:
* doc/misc/semantic.texi, doc/misc/ses.texi, doc/misc/sieve.texi:
* doc/misc/smtpmail.texi, doc/misc/speedbar.texi:
* doc/misc/srecode.texi, doc/misc/todo-mode.texi, doc/misc/tramp.texi:
* doc/misc/url.texi, doc/misc/vhdl-mode.texi, doc/misc/vip.texi:
* doc/misc/viper.texi, doc/misc/widget.texi, doc/misc/wisent.texi:
* doc/misc/woman.texi:
Use it instead of '@documentencoding UTF-8', to lessen the need for
global changes like this in the future.
* doc/emacs/Makefile.in (EMACS_XTRA):
* doc/lispintro/Makefile.in (srcs):
* doc/lispref/Makefile.in (srcs):
Add dependency on docstyle.texi.
* doc/misc/Makefile.in (style): New macro.
(${buildinfodir}/%.info, %.dvi, %.pdf, %.html)
(${buildinfodir}/ccmode.info, ${buildinfodir}/efaq%.info, gnus_deps):
Use it.
2015-05-01 19:05:53 +00:00
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@include docstyle.texi
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2012-12-13 04:44:07 +00:00
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@c *************************************************************************
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@c @ Header
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@c *************************************************************************
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@c Merge all indexes into a single index for now.
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@c We can always separate them later into two or more as needed.
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@syncodeindex vr cp
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@syncodeindex fn cp
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@syncodeindex ky cp
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@syncodeindex pg cp
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@syncodeindex tp cp
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@c @footnotestyle separate
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@c @paragraphindent 2
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@c @@smallbook
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@c %**end of header
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@copying
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2018-01-01 09:02:09 +00:00
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Copyright @copyright{} 1988--1993, 1995, 1998--2004, 2007, 2012--2018
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Free Software Foundation, Inc.
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@c Since we are both GNU manuals, we do not need to ack each other here.
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@ignore
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2012-12-13 04:44:07 +00:00
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Some texts are borrowed or adapted from the manual of Bison version
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1.35. The text in section entitled ``Understanding the automaton'' is
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adapted from the section ``Understanding Your Parser'' in the manual
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of Bison version 1.49.
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@end ignore
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@quotation
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Permission is granted to copy, distribute and/or modify this document
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2012-12-13 04:47:14 +00:00
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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2014-05-07 17:34:53 +00:00
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Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
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2012-12-13 04:47:14 +00:00
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and with the Back-Cover Texts as in (a) below. A copy of the license
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is included in the section entitled ``GNU Free Documentation License''.
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(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
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modify this GNU manual.''
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@end quotation
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@end copying
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@dircategory Emacs misc features
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@direntry
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* Wisent: (wisent). Semantic Wisent parser development.
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@end direntry
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@iftex
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@finalout
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@end iftex
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@c @setchapternewpage odd
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@c @setchapternewpage off
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@titlepage
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@sp 10
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@title @value{TITLE}
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@author by @value{AUTHOR}
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@page
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@vskip 0pt plus 1 fill
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@insertcopying
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@end titlepage
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@page
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2012-12-13 04:47:14 +00:00
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@macro semantic{}
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@i{Semantic}
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@end macro
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2012-12-13 04:44:07 +00:00
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@c *************************************************************************
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@c @ Document
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@c *************************************************************************
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@contents
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@node top
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@top @value{TITLE}
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Wisent (the European Bison ;-) is an Emacs Lisp implementation of the
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GNU Compiler Compiler Bison.
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This manual describes how to use Wisent to develop grammars for
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programming languages, and how to use grammars to parse language
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source in Emacs buffers.
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It also describes how Wisent is used with the @semantic{} tool set
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described in the @ref{Top, Semantic Manual, Semantic Manual, semantic}.
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2012-12-13 04:47:14 +00:00
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@ifnottex
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@insertcopying
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@end ifnottex
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2012-12-13 04:44:07 +00:00
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@menu
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2012-12-13 04:47:14 +00:00
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* Wisent Overview::
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* Wisent Grammar::
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* Wisent Parsing::
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* Wisent Semantic::
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* GNU Free Documentation License::
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* Index::
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2012-12-13 04:44:07 +00:00
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@end menu
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@node Wisent Overview
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@chapter Wisent Overview
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@dfn{Wisent} (the European Bison) is an implementation in Emacs Lisp
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of the GNU Compiler Compiler Bison. Its code is a port of the C code
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of GNU Bison 1.28 & 1.31.
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For more details on the basic concepts for understanding Wisent, it is
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2012-12-22 21:58:06 +00:00
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worthwhile to read the @ref{Top, Bison Manual, , bison}.
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2012-12-13 04:44:07 +00:00
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Wisent can generate compilers compatible with the @semantic{} tool set.
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See the @ref{Top, Semantic Manual, , semantic}.
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It benefits from these Bison features:
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@itemize @bullet
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2012-12-13 04:47:14 +00:00
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@item
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2012-12-13 04:44:07 +00:00
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It uses a fast but not so space-efficient encoding for the parse
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tables, described in Corbett's PhD thesis from Berkeley:
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@quotation
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@cite{Static Semantics in Compiler Error Recovery}@*
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June 1985, Report No. UCB/CSD 85/251.
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@end quotation
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@item
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For generating the lookahead sets, Wisent uses the well-known
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2014-01-16 06:24:06 +00:00
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technique of F. DeRemer and T. Pennello described in:
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@quotation
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2012-12-14 20:05:03 +00:00
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@cite{Efficient Computation of LALR(1) Look-Ahead Sets}@*
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October 1982, ACM TOPLAS Vol 4 No 4, 615--49,
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@uref{http://dx.doi.org/10.1145/69622.357187}.
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@end quotation
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@item
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Wisent resolves shift/reduce conflicts using operator precedence and
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associativity.
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2012-12-13 04:47:14 +00:00
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@item
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2012-12-13 04:44:07 +00:00
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Parser error recovery is accomplished using rules which match the
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special token @code{error}.
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@end itemize
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Nevertheless there are some fundamental differences between Bison and
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Wisent.
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@itemize
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@item
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Wisent is intended to be used in Emacs. It reads and produces Emacs
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Lisp data structures. All the additional code used in grammars is
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Emacs Lisp code.
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@item
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Contrary to Bison, Wisent does not generate a parser which combines
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Emacs Lisp code and grammar constructs. They exist separately.
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Wisent reads the grammar from a Lisp data structure and then generates
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grammar constructs as tables. Afterward, the derived tables can be
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included and byte-compiled in separate Emacs Lisp files, and be used
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at a later time by the Wisent's parser engine.
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@item
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Wisent allows multiple start nonterminals and allows a call to the
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parsing function to be made for a particular start nonterminal. For
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example, this is particularly useful to parse a region of an Emacs
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buffer. @semantic{} heavily depends on the availability of this feature.
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@end itemize
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@node Wisent Grammar
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@chapter Wisent Grammar
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@cindex context-free grammar
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@cindex rule
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In order for Wisent to parse a language, it must be described by a
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@dfn{context-free grammar}. That is a grammar specified as rules that
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can be applied regardless of context. For more information, see
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@ref{Language and Grammar, , , bison}, in the Bison manual.
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@cindex terminal
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@cindex nonterminal
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The formal grammar is formulated using @dfn{terminal} and
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@dfn{nonterminal} items. Terminals can be Emacs Lisp symbols or
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characters, and nonterminals are symbols only.
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@cindex token
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Terminals (also known as @dfn{tokens}) represent the lexical
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elements of the language like numbers, strings, etc..
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For example @samp{PLUS} can represent the operator @samp{+}.
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Nonterminal symbols are described by rules:
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@example
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@group
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RESULT @equiv{} COMPONENTS@dots{}
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@end group
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@end example
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@samp{RESULT} is a nonterminal that this rule describes and
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@samp{COMPONENTS} are various terminals and nonterminals that are put
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together by this rule.
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For example, this rule:
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@example
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@group
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exp @equiv{} exp PLUS exp
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@end group
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@end example
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Says that two groupings of type @samp{exp}, with a @samp{PLUS} token
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in between, can be combined into a larger grouping of type @samp{exp}.
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2012-12-13 04:44:07 +00:00
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@menu
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2012-12-13 04:47:14 +00:00
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* Grammar format::
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* Example::
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* Compiling a grammar::
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* Conflicts::
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2012-12-13 04:44:07 +00:00
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@end menu
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2012-12-22 20:19:41 +00:00
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@node Grammar format
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2012-12-13 04:44:07 +00:00
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@section Grammar format
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@cindex grammar format
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To be acceptable by Wisent a context-free grammar must respect a
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particular format. That is, must be represented as an Emacs Lisp list
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of the form:
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@code{(@var{terminals} @var{assocs} . @var{non-terminals})}
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@table @var
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@item terminals
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Is the list of terminal symbols used in the grammar.
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@cindex associativity
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@item assocs
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Specify the associativity of @var{terminals}. It is @code{nil} when
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there is no associativity defined, or an alist of
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@w{@code{(@var{assoc-type} . @var{assoc-value})}} elements.
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@var{assoc-type} must be one of the @code{default-prec},
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@code{nonassoc}, @code{left} or @code{right} symbols. When
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@var{assoc-type} is @code{default-prec}, @var{assoc-value} must be
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@code{nil} or @code{t} (the default). Otherwise it is a list of
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tokens which must have been previously declared in @var{terminals}.
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For details, see @ref{Contextual Precedence, , , bison}, in the
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Bison manual.
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@item non-terminals
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Is the list of nonterminal definitions. Each definition has the form:
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@code{(@var{nonterm} . @var{rules})}
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Where @var{nonterm} is the nonterminal symbol defined and
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@var{rules} the list of rules that describe this nonterminal. Each
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rule is a list:
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@code{(@var{components} [@var{precedence}] [@var{action}])}
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Where:
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@table @var
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@item components
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Is a list of various terminals and nonterminals that are put together
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by this rule.
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For example,
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@example
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@group
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(exp ((exp ?+ exp)) ;; exp: exp '+' exp
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) ;; ;
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@end group
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@end example
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Says that two groupings of type @samp{exp}, with a @samp{+} token in
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between, can be combined into a larger grouping of type @samp{exp}.
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2012-12-14 20:05:03 +00:00
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2012-12-13 04:44:07 +00:00
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@cindex grammar coding conventions
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By convention, a nonterminal symbol should be in lower case, such as
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@samp{exp}, @samp{stmt} or @samp{declaration}. Terminal symbols
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should be upper case to distinguish them from nonterminals: for
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example, @samp{INTEGER}, @samp{IDENTIFIER}, @samp{IF} or
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@samp{RETURN}. A terminal symbol that represents a particular keyword
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in the language is conventionally the same as that keyword converted
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to upper case. The terminal symbol @code{error} is reserved for error
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recovery.
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@cindex middle-rule actions
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Scattered among the components can be @dfn{middle-rule} actions.
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Usually only @var{action} is provided (@pxref{action}).
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|
|
If @var{components} in a rule is @code{nil}, it means that the rule
|
|
|
|
can match the empty string. For example, here is how to define a
|
|
|
|
comma-separated sequence of zero or more @samp{exp} groupings:
|
|
|
|
|
2012-12-22 21:58:06 +00:00
|
|
|
@smallexample
|
2012-12-13 04:44:07 +00:00
|
|
|
@group
|
|
|
|
(expseq (nil) ;; expseq: ;; empty
|
|
|
|
((expseq1)) ;; | expseq1
|
|
|
|
) ;; ;
|
|
|
|
|
|
|
|
(expseq1 ((exp)) ;; expseq1: exp
|
|
|
|
((expseq1 ?, exp)) ;; | expseq1 ',' exp
|
|
|
|
) ;; ;
|
|
|
|
@end group
|
2012-12-22 21:58:06 +00:00
|
|
|
@end smallexample
|
2012-12-13 04:44:07 +00:00
|
|
|
|
|
|
|
@cindex precedence level
|
|
|
|
@item precedence
|
|
|
|
Assign the rule the precedence of the given terminal item, overriding
|
|
|
|
the precedence that would be deduced for it, that is the one of the
|
|
|
|
last terminal in it. Notice that only terminals declared in
|
|
|
|
@var{assocs} have a precedence level. The altered rule precedence
|
|
|
|
then affects how conflicts involving that rule are resolved.
|
|
|
|
|
|
|
|
@var{precedence} is an optional vector of one terminal item.
|
|
|
|
|
|
|
|
Here is how @var{precedence} solves the problem of unary minus.
|
|
|
|
First, declare a precedence for a fictitious terminal symbol named
|
|
|
|
@code{UMINUS}. There are no tokens of this type, but the symbol
|
|
|
|
serves to stand for its precedence:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@dots{}
|
|
|
|
((default-prec t) ;; This is the default
|
|
|
|
(left '+' '-')
|
|
|
|
(left '*')
|
|
|
|
(left UMINUS))
|
|
|
|
@end example
|
|
|
|
|
|
|
|
Now the precedence of @code{UMINUS} can be used in specific rules:
|
|
|
|
|
2012-12-22 21:58:06 +00:00
|
|
|
@smallexample
|
2012-12-13 04:44:07 +00:00
|
|
|
@group
|
|
|
|
(exp @dots{} ;; exp: @dots{}
|
|
|
|
((exp ?- exp)) ;; | exp '-' exp
|
|
|
|
@dots{} ;; @dots{}
|
|
|
|
((?- exp) [UMINUS]) ;; | '-' exp %prec UMINUS
|
|
|
|
@dots{} ;; @dots{}
|
|
|
|
) ;; ;
|
|
|
|
@end group
|
2012-12-22 21:58:06 +00:00
|
|
|
@end smallexample
|
2012-12-13 04:44:07 +00:00
|
|
|
|
|
|
|
If you forget to append @code{[UMINUS]} to the rule for unary minus,
|
|
|
|
Wisent silently assumes that minus has its usual precedence. This
|
|
|
|
kind of problem can be tricky to debug, since one typically discovers
|
|
|
|
the mistake only by testing the code.
|
|
|
|
|
|
|
|
Using @code{(default-prec nil)} declaration makes it easier to
|
|
|
|
discover this kind of problem systematically. It causes rules that
|
|
|
|
lack a @var{precedence} modifier to have no precedence, even if the
|
|
|
|
last terminal symbol mentioned in their components has a declared
|
|
|
|
precedence.
|
|
|
|
|
|
|
|
If @code{(default-prec nil)} is in effect, you must specify
|
|
|
|
@var{precedence} for all rules that participate in precedence conflict
|
|
|
|
resolution. Then you will see any shift/reduce conflict until you
|
|
|
|
tell Wisent how to resolve it, either by changing your grammar or by
|
|
|
|
adding an explicit precedence. This will probably add declarations to
|
|
|
|
the grammar, but it helps to protect against incorrect rule
|
|
|
|
precedences.
|
|
|
|
|
|
|
|
The effect of @code{(default-prec nil)} can be reversed by giving
|
|
|
|
@code{(default-prec t)}, which is the default.
|
|
|
|
|
|
|
|
For more details, see @ref{Contextual Precedence, , , bison}, in the
|
|
|
|
Bison manual.
|
|
|
|
|
|
|
|
It is important to understand that @var{assocs} declarations defines
|
|
|
|
associativity but also assign a precedence level to terminals. All
|
|
|
|
terminals declared in the same @code{left}, @code{right} or
|
|
|
|
@code{nonassoc} association get the same precedence level. The
|
|
|
|
precedence level is increased at each new association.
|
|
|
|
|
|
|
|
On the other hand, @var{precedence} explicitly assign the precedence
|
|
|
|
level of the given terminal to a rule.
|
|
|
|
|
|
|
|
@cindex semantic actions
|
|
|
|
@item @anchor{action}action
|
|
|
|
An action is an optional Emacs Lisp function call, like this:
|
|
|
|
|
|
|
|
@code{(identity $1)}
|
|
|
|
|
|
|
|
The result of an action determines the semantic value of a rule.
|
|
|
|
|
|
|
|
From an implementation standpoint, the function call will be embedded
|
|
|
|
in a lambda expression, and several useful local variables will be
|
|
|
|
defined:
|
|
|
|
|
|
|
|
@table @code
|
|
|
|
@vindex $N
|
|
|
|
@item $@var{n}
|
|
|
|
Where @var{n} is a positive integer. Like in Bison, the value of
|
|
|
|
@code{$@var{n}} is the semantic value of the @var{n}th element of
|
|
|
|
@var{components}, starting from 1. It can be of any Lisp data
|
|
|
|
type.
|
|
|
|
|
|
|
|
@vindex $region@var{n}
|
|
|
|
@item $regionN
|
|
|
|
Where @var{n} is a positive integer. For each @code{$@var{n}}
|
|
|
|
variable defined there is a corresponding @code{$region@var{n}}
|
|
|
|
variable. Its value is a pair @code{(@var{start-pos} .
|
|
|
|
@var{end-pos})} that represent the start and end positions (in the
|
|
|
|
lexical input stream) of the @code{$@var{n}} value. It can be
|
|
|
|
@code{nil} when the component positions are not available, like for an
|
|
|
|
empty string component for example.
|
|
|
|
|
|
|
|
@vindex $region
|
|
|
|
@item $region
|
|
|
|
Its value is the leftmost and rightmost positions of input data
|
|
|
|
matched by all @var{components} in the rule. This is a pair
|
|
|
|
@code{(@var{leftmost-pos} . @var{rightmost-pos})}. It can be
|
|
|
|
@code{nil} when components positions are not available.
|
|
|
|
|
|
|
|
@vindex $nterm
|
|
|
|
@item $nterm
|
|
|
|
This variable is initialized with the nonterminal symbol
|
|
|
|
(@var{nonterm}) the rule belongs to. It could be useful to improve
|
|
|
|
error reporting or debugging. It is also used to automatically
|
|
|
|
provide incremental re-parse entry points for @semantic{} tags
|
|
|
|
(@pxref{Wisent Semantic}).
|
|
|
|
|
|
|
|
@vindex $action
|
|
|
|
@item $action
|
|
|
|
The value of @code{$action} is the symbolic name of the current
|
|
|
|
semantic action (@pxref{Debugging actions}).
|
|
|
|
@end table
|
|
|
|
|
|
|
|
When an action is not specified a default value is supplied, it is
|
|
|
|
@code{(identity $1)}. This means that the default semantic value of a
|
|
|
|
rule is the value of its first component. Excepted for a rule
|
|
|
|
matching the empty string, for which the default action is to return
|
|
|
|
@code{nil}.
|
|
|
|
@end table
|
|
|
|
@end table
|
|
|
|
|
2012-12-22 20:19:41 +00:00
|
|
|
@node Example
|
2012-12-13 04:44:07 +00:00
|
|
|
@section Example
|
|
|
|
|
|
|
|
@cindex grammar example
|
|
|
|
Here is an example to parse simple infix arithmetic expressions. See
|
|
|
|
@ref{Infix Calc, , , bison}, in the Bison manual for details.
|
|
|
|
|
|
|
|
@lisp
|
|
|
|
@group
|
|
|
|
'(
|
|
|
|
;; Terminals
|
|
|
|
(NUM)
|
2012-12-13 04:47:14 +00:00
|
|
|
|
2012-12-13 04:44:07 +00:00
|
|
|
;; Terminal associativity & precedence
|
|
|
|
((nonassoc ?=)
|
|
|
|
(left ?- ?+)
|
|
|
|
(left ?* ?/)
|
|
|
|
(left NEG)
|
|
|
|
(right ?^))
|
2012-12-13 04:47:14 +00:00
|
|
|
|
2012-12-13 04:44:07 +00:00
|
|
|
;; Rules
|
|
|
|
(input
|
|
|
|
((line))
|
|
|
|
((input line)
|
|
|
|
(format "%s %s" $1 $2))
|
|
|
|
)
|
|
|
|
|
|
|
|
(line
|
|
|
|
((?;)
|
|
|
|
(progn ";"))
|
|
|
|
((exp ?;)
|
|
|
|
(format "%s;" $1))
|
|
|
|
((error ?;)
|
|
|
|
(progn "Error;")))
|
|
|
|
)
|
|
|
|
|
|
|
|
(exp
|
|
|
|
((NUM)
|
|
|
|
(string-to-number $1))
|
|
|
|
((exp ?= exp)
|
|
|
|
(= $1 $3))
|
|
|
|
((exp ?+ exp)
|
|
|
|
(+ $1 $3))
|
|
|
|
((exp ?- exp)
|
|
|
|
(- $1 $3))
|
|
|
|
((exp ?* exp)
|
|
|
|
(* $1 $3))
|
|
|
|
((exp ?/ exp)
|
|
|
|
(/ $1 $3))
|
|
|
|
((?- exp) [NEG]
|
|
|
|
(- $2))
|
|
|
|
((exp ?^ exp)
|
|
|
|
(expt $1 $3))
|
|
|
|
((?\( exp ?\))
|
|
|
|
(progn $2))
|
|
|
|
)
|
|
|
|
)
|
|
|
|
@end group
|
|
|
|
@end lisp
|
|
|
|
|
|
|
|
In the bison-like @dfn{WY} format (@pxref{Wisent Semantic}) the
|
|
|
|
grammar looks like this:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
%token <number> NUM
|
|
|
|
|
|
|
|
%nonassoc '=' ;; comparison
|
|
|
|
%left '-' '+'
|
|
|
|
%left '*' '/'
|
|
|
|
%left NEG ;; negation--unary minus
|
|
|
|
%right '^' ;; exponentiation
|
|
|
|
|
|
|
|
%%
|
|
|
|
|
|
|
|
input:
|
|
|
|
line
|
|
|
|
| input line
|
|
|
|
(format "%s %s" $1 $2)
|
|
|
|
;
|
|
|
|
|
|
|
|
line:
|
|
|
|
';'
|
|
|
|
@{";"@}
|
|
|
|
| exp ';'
|
|
|
|
(format "%s;" $1)
|
|
|
|
| error ';'
|
|
|
|
@{"Error;"@}
|
|
|
|
;
|
|
|
|
|
|
|
|
exp:
|
|
|
|
NUM
|
|
|
|
(string-to-number $1)
|
|
|
|
| exp '=' exp
|
|
|
|
(= $1 $3)
|
|
|
|
| exp '+' exp
|
|
|
|
(+ $1 $3)
|
|
|
|
| exp '-' exp
|
|
|
|
(- $1 $3)
|
|
|
|
| exp '*' exp
|
|
|
|
(* $1 $3)
|
|
|
|
| exp '/' exp
|
|
|
|
(/ $1 $3)
|
|
|
|
| '-' exp %prec NEG
|
|
|
|
(- $2)
|
|
|
|
| exp '^' exp
|
|
|
|
(expt $1 $3)
|
|
|
|
| '(' exp ')'
|
|
|
|
@{$2@}
|
|
|
|
;
|
|
|
|
|
|
|
|
%%
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
2012-12-22 20:19:41 +00:00
|
|
|
@node Compiling a grammar
|
2012-12-13 04:44:07 +00:00
|
|
|
@section Compiling a grammar
|
|
|
|
|
|
|
|
@cindex automaton
|
|
|
|
After providing a context-free grammar in a suitable format, it must
|
|
|
|
be translated into a set of tables (an @dfn{automaton}) that will be
|
|
|
|
used to derive the parser. Like Bison, Wisent translates grammars that
|
|
|
|
must be @dfn{LALR(1)}.
|
|
|
|
|
|
|
|
@cindex LALR(1) grammar
|
|
|
|
@cindex look-ahead token
|
|
|
|
A grammar is @acronym{LALR(1)} if it is possible to tell how to parse
|
|
|
|
any portion of an input string with just a single token of look-ahead:
|
|
|
|
the @dfn{look-ahead token}. See @ref{Language and Grammar, , ,
|
|
|
|
bison}, in the Bison manual for more information.
|
|
|
|
|
|
|
|
@cindex grammar compilation
|
|
|
|
Grammar translation (compilation) is achieved by the function:
|
|
|
|
|
|
|
|
@cindex compiling a grammar
|
|
|
|
@vindex wisent-single-start-flag
|
|
|
|
@findex wisent-compile-grammar
|
|
|
|
@defun wisent-compile-grammar grammar &optional start-list
|
|
|
|
Compile @var{grammar} and return an @acronym{LALR(1)} automaton.
|
|
|
|
|
|
|
|
Optional argument @var{start-list} is a list of start symbols
|
|
|
|
(nonterminals). If @code{nil} the first nonterminal defined in the
|
|
|
|
grammar is the default start symbol. If @var{start-list} contains
|
|
|
|
only one element, it defines the start symbol. If @var{start-list}
|
|
|
|
contains more than one element, all are defined as potential start
|
|
|
|
symbols, unless @code{wisent-single-start-flag} is non-@code{nil}. In
|
|
|
|
that case the first element of @var{start-list} defines the start
|
|
|
|
symbol and others are ignored.
|
|
|
|
|
|
|
|
The @acronym{LALR(1)} automaton is a vector of the form:
|
|
|
|
|
|
|
|
@code{[@var{actions gotos starts functions}]}
|
|
|
|
|
|
|
|
@table @var
|
|
|
|
@item actions
|
|
|
|
A state/token matrix telling the parser what to do at every state
|
|
|
|
based on the current look-ahead token. That is shift, reduce, accept
|
|
|
|
or error. See also @ref{Wisent Parsing}.
|
|
|
|
|
|
|
|
@item gotos
|
|
|
|
A state/nonterminal matrix telling the parser the next state to go to
|
|
|
|
after reducing with each rule.
|
|
|
|
|
|
|
|
@item starts
|
|
|
|
An alist which maps the allowed start symbols (nonterminals) to
|
|
|
|
lexical tokens that will be first shifted into the parser stack.
|
|
|
|
|
|
|
|
@item functions
|
|
|
|
An obarray of semantic action symbols. A semantic action is actually
|
|
|
|
an Emacs Lisp function (lambda expression).
|
|
|
|
@end table
|
|
|
|
@end defun
|
|
|
|
|
2012-12-22 20:19:41 +00:00
|
|
|
@node Conflicts
|
2012-12-13 04:44:07 +00:00
|
|
|
@section Conflicts
|
|
|
|
|
|
|
|
Normally, a grammar should produce an automaton where at each state
|
|
|
|
the parser has only one action to do (@pxref{Wisent Parsing}).
|
|
|
|
|
|
|
|
@cindex ambiguous grammar
|
|
|
|
In certain cases, a grammar can produce an automaton where, at some
|
|
|
|
states, there are more than one action possible. Such a grammar is
|
|
|
|
@dfn{ambiguous}, and generates @dfn{conflicts}.
|
|
|
|
|
|
|
|
@cindex deterministic automaton
|
|
|
|
The parser can't be driven by an automaton which isn't completely
|
|
|
|
@dfn{deterministic}, that is which contains conflicts. It is
|
|
|
|
necessary to resolve the conflicts to eliminate them. Wisent resolves
|
|
|
|
conflicts like Bison does.
|
|
|
|
|
|
|
|
@cindex grammar conflicts
|
|
|
|
@cindex conflicts resolution
|
|
|
|
There are two sorts of conflicts:
|
|
|
|
|
|
|
|
@table @dfn
|
|
|
|
@cindex shift/reduce conflicts
|
|
|
|
@item shift/reduce conflicts
|
|
|
|
When either a shift or a reduction would be valid at the same state.
|
|
|
|
|
|
|
|
Such conflicts are resolved by choosing to shift, unless otherwise
|
|
|
|
directed by operator precedence declarations.
|
|
|
|
See @ref{Shift/Reduce , , , bison}, in the Bison manual for more
|
|
|
|
information.
|
|
|
|
|
|
|
|
@cindex reduce/reduce conflicts
|
|
|
|
@item reduce/reduce conflicts
|
|
|
|
That occurs if there are two or more rules that apply to the same
|
|
|
|
sequence of input. This usually indicates a serious error in the
|
|
|
|
grammar.
|
|
|
|
|
|
|
|
Such conflicts are resolved by choosing to use the rule that appears
|
|
|
|
first in the grammar, but it is very risky to rely on this. Every
|
|
|
|
reduce/reduce conflict must be studied and usually eliminated. See
|
|
|
|
@ref{Reduce/Reduce , , , bison}, in the Bison manual for more
|
|
|
|
information.
|
|
|
|
@end table
|
|
|
|
|
|
|
|
@menu
|
2012-12-13 04:47:14 +00:00
|
|
|
* Grammar Debugging::
|
|
|
|
* Understanding the automaton::
|
2012-12-13 04:44:07 +00:00
|
|
|
@end menu
|
|
|
|
|
|
|
|
@node Grammar Debugging
|
|
|
|
@subsection Grammar debugging
|
|
|
|
|
|
|
|
@cindex grammar debugging
|
|
|
|
@cindex grammar verbose description
|
|
|
|
To help writing a new grammar, @code{wisent-compile-grammar} can
|
|
|
|
produce a verbose report containing a detailed description of the
|
|
|
|
grammar and parser (equivalent to what Bison reports with the
|
|
|
|
@option{--verbose} option).
|
|
|
|
|
|
|
|
To enable the verbose report you can set to non-@code{nil} the
|
|
|
|
variable:
|
|
|
|
|
|
|
|
@vindex wisent-verbose-flag
|
|
|
|
@deffn Option wisent-verbose-flag
|
|
|
|
non-@code{nil} means to report verbose information on generated parser.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
Or interactively use the command:
|
|
|
|
|
|
|
|
@findex wisent-toggle-verbose-flag
|
|
|
|
@deffn Command wisent-toggle-verbose-flag
|
|
|
|
Toggle whether to report verbose information on generated parser.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
The verbose report is printed in the temporary buffer
|
Use @file for buffers, per the Texinfo manual
* doc/misc/ada-mode.texi, doc/misc/auth.texi, doc/misc/calc.texi:
* doc/misc/ebrowse.texi, doc/misc/efaq.texi, doc/misc/emacs-gnutls.texi:
* doc/misc/epa.texi, doc/misc/ert.texi, doc/misc/eshell.texi:
* doc/misc/eww.texi, doc/misc/flymake.texi, doc/misc/gnus.texi:
* doc/misc/info.texi, doc/misc/message.texi, doc/misc/mh-e.texi:
* doc/misc/newsticker.texi, doc/misc/pcl-cvs.texi, doc/misc/rcirc.texi:
* doc/misc/sem-user.texi, doc/misc/smtpmail.texi, doc/misc/url.texi:
* doc/misc/viper.texi, doc/misc/wisent.texi, doc/misc/woman.texi:
Use @file for buffers, per the Texinfo manual.
2014-03-12 20:52:34 +00:00
|
|
|
@file{*wisent-log*} when running interactively, or in file
|
2012-12-13 04:44:07 +00:00
|
|
|
@file{wisent.output} when running in batch mode. Different
|
|
|
|
reports are separated from each other by a line like this:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
*** Wisent @var{source-file} - 2002-06-27 17:33
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
where @var{source-file} is the name of the Emacs Lisp file from which
|
|
|
|
the grammar was read. See @ref{Understanding the automaton}, for
|
|
|
|
details on the verbose report.
|
|
|
|
|
|
|
|
@table @strong
|
|
|
|
@item Please Note
|
|
|
|
To help debugging the grammar compiler itself, you can set this
|
|
|
|
variable to print the content of some internal data structures:
|
|
|
|
|
|
|
|
@vindex wisent-debug-flag
|
|
|
|
@defvar wisent-debug-flag
|
|
|
|
non-@code{nil} means enable some debug stuff.
|
|
|
|
@end defvar
|
|
|
|
@end table
|
|
|
|
|
|
|
|
@node Understanding the automaton
|
|
|
|
@subsection Understanding the automaton
|
|
|
|
|
|
|
|
@cindex understanding the automaton
|
|
|
|
This section (took from the manual of Bison 1.49) describes how to use
|
|
|
|
the verbose report printed by @code{wisent-compile-grammar} to
|
|
|
|
understand the generated automaton, to tune or fix a grammar.
|
|
|
|
|
|
|
|
We will use the following example:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
(let ((wisent-verbose-flag t)) ;; Print a verbose report!
|
|
|
|
(wisent-compile-grammar
|
|
|
|
'((NUM STR) ; %token NUM STR
|
|
|
|
|
2012-12-13 04:47:14 +00:00
|
|
|
((left ?+ ?-) ; %left '+' '-';
|
2012-12-13 04:44:07 +00:00
|
|
|
(left ?*)) ; %left '*'
|
|
|
|
|
|
|
|
(exp ; exp:
|
|
|
|
((exp ?+ exp)) ; exp '+' exp
|
|
|
|
((exp ?- exp)) ; | exp '-' exp
|
|
|
|
((exp ?* exp)) ; | exp '*' exp
|
|
|
|
((exp ?/ exp)) ; | exp '/' exp
|
|
|
|
((NUM)) ; | NUM
|
|
|
|
) ; ;
|
|
|
|
|
|
|
|
(useless ; useless:
|
|
|
|
((STR)) ; STR
|
|
|
|
) ; ;
|
|
|
|
)
|
|
|
|
'nil) ; no %start declarations
|
|
|
|
)
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
When evaluating the above expression, grammar compilation first issues
|
|
|
|
the following two clear messages:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
Grammar contains 1 useless nonterminals and 1 useless rules
|
|
|
|
Grammar contains 7 shift/reduce conflicts
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
Use @file for buffers, per the Texinfo manual
* doc/misc/ada-mode.texi, doc/misc/auth.texi, doc/misc/calc.texi:
* doc/misc/ebrowse.texi, doc/misc/efaq.texi, doc/misc/emacs-gnutls.texi:
* doc/misc/epa.texi, doc/misc/ert.texi, doc/misc/eshell.texi:
* doc/misc/eww.texi, doc/misc/flymake.texi, doc/misc/gnus.texi:
* doc/misc/info.texi, doc/misc/message.texi, doc/misc/mh-e.texi:
* doc/misc/newsticker.texi, doc/misc/pcl-cvs.texi, doc/misc/rcirc.texi:
* doc/misc/sem-user.texi, doc/misc/smtpmail.texi, doc/misc/url.texi:
* doc/misc/viper.texi, doc/misc/wisent.texi, doc/misc/woman.texi:
Use @file for buffers, per the Texinfo manual.
2014-03-12 20:52:34 +00:00
|
|
|
The @file{*wisent-log*} buffer details things!
|
2012-12-13 04:44:07 +00:00
|
|
|
|
|
|
|
The first section reports conflicts that were solved using precedence
|
|
|
|
and/or associativity:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
Conflict in state 7 between rule 1 and token '+' resolved as reduce.
|
|
|
|
Conflict in state 7 between rule 1 and token '-' resolved as reduce.
|
|
|
|
Conflict in state 7 between rule 1 and token '*' resolved as shift.
|
|
|
|
Conflict in state 8 between rule 2 and token '+' resolved as reduce.
|
|
|
|
Conflict in state 8 between rule 2 and token '-' resolved as reduce.
|
|
|
|
Conflict in state 8 between rule 2 and token '*' resolved as shift.
|
|
|
|
Conflict in state 9 between rule 3 and token '+' resolved as reduce.
|
|
|
|
Conflict in state 9 between rule 3 and token '-' resolved as reduce.
|
|
|
|
Conflict in state 9 between rule 3 and token '*' resolved as reduce.
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The next section reports useless tokens, nonterminal and rules (note
|
|
|
|
that useless tokens might be used by the scanner):
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
Useless nonterminals:
|
|
|
|
|
|
|
|
useless
|
|
|
|
|
|
|
|
|
|
|
|
Terminals which are not used:
|
|
|
|
|
|
|
|
STR
|
|
|
|
|
|
|
|
|
|
|
|
Useless rules:
|
|
|
|
|
|
|
|
#6 useless: STR;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The next section lists states that still have conflicts:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
State 7 contains 1 shift/reduce conflict.
|
|
|
|
State 8 contains 1 shift/reduce conflict.
|
|
|
|
State 9 contains 1 shift/reduce conflict.
|
|
|
|
State 10 contains 4 shift/reduce conflicts.
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The next section reproduces the grammar used:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
Grammar
|
|
|
|
|
|
|
|
Number, Rule
|
|
|
|
1 exp -> exp '+' exp
|
|
|
|
2 exp -> exp '-' exp
|
|
|
|
3 exp -> exp '*' exp
|
|
|
|
4 exp -> exp '/' exp
|
|
|
|
5 exp -> NUM
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
And reports the uses of the symbols:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
Terminals, with rules where they appear
|
|
|
|
|
|
|
|
$EOI (-1)
|
|
|
|
error (1)
|
|
|
|
NUM (2) 5
|
|
|
|
STR (3) 6
|
|
|
|
'+' (4) 1
|
|
|
|
'-' (5) 2
|
|
|
|
'*' (6) 3
|
|
|
|
'/' (7) 4
|
|
|
|
|
|
|
|
|
|
|
|
Nonterminals, with rules where they appear
|
|
|
|
|
|
|
|
exp (8)
|
|
|
|
on left: 1 2 3 4 5, on right: 1 2 3 4
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The report then details the automaton itself, describing each state
|
|
|
|
with it set of @dfn{items}, also known as @dfn{pointed rules}. Each
|
|
|
|
item is a production rule together with a point (marked by @samp{.})
|
|
|
|
that the input cursor.
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 0
|
|
|
|
|
|
|
|
NUM shift, and go to state 1
|
|
|
|
|
|
|
|
exp go to state 2
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
State 0 corresponds to being at the very beginning of the parsing, in
|
|
|
|
the initial rule, right before the start symbol (@samp{exp}). When
|
|
|
|
the parser returns to this state right after having reduced a rule
|
|
|
|
that produced an @samp{exp}, it jumps to state 2. If there is no such
|
|
|
|
transition on a nonterminal symbol, and the lookahead is a @samp{NUM},
|
|
|
|
then this token is shifted on the parse stack, and the control flow
|
|
|
|
jumps to state 1. Any other lookahead triggers a parse error.
|
|
|
|
|
|
|
|
In the state 1...
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 1
|
|
|
|
|
|
|
|
exp -> NUM . (rule 5)
|
|
|
|
|
|
|
|
$default reduce using rule 5 (exp)
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
the rule 5, @samp{exp: NUM;}, is completed. Whatever the lookahead
|
|
|
|
(@samp{$default}), the parser will reduce it. If it was coming from
|
|
|
|
state 0, then, after this reduction it will return to state 0, and
|
|
|
|
will jump to state 2 (@samp{exp: go to state 2}).
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 2
|
|
|
|
|
|
|
|
exp -> exp . '+' exp (rule 1)
|
|
|
|
exp -> exp . '-' exp (rule 2)
|
|
|
|
exp -> exp . '*' exp (rule 3)
|
|
|
|
exp -> exp . '/' exp (rule 4)
|
|
|
|
|
|
|
|
$EOI shift, and go to state 11
|
|
|
|
'+' shift, and go to state 3
|
|
|
|
'-' shift, and go to state 4
|
|
|
|
'*' shift, and go to state 5
|
|
|
|
'/' shift, and go to state 6
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
In state 2, the automaton can only shift a symbol. For instance,
|
|
|
|
because of the item @samp{exp -> exp . '+' exp}, if the lookahead if
|
|
|
|
@samp{+}, it will be shifted on the parse stack, and the automaton
|
|
|
|
control will jump to state 3, corresponding to the item
|
|
|
|
@samp{exp -> exp . '+' exp}:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 3
|
|
|
|
|
|
|
|
exp -> exp '+' . exp (rule 1)
|
|
|
|
|
|
|
|
NUM shift, and go to state 1
|
|
|
|
|
|
|
|
exp go to state 7
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
Since there is no default action, any other token than those listed
|
|
|
|
above will trigger a parse error.
|
|
|
|
|
|
|
|
The interpretation of states 4 to 6 is straightforward:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 4
|
|
|
|
|
|
|
|
exp -> exp '-' . exp (rule 2)
|
|
|
|
|
|
|
|
NUM shift, and go to state 1
|
|
|
|
|
|
|
|
exp go to state 8
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
state 5
|
|
|
|
|
|
|
|
exp -> exp '*' . exp (rule 3)
|
|
|
|
|
|
|
|
NUM shift, and go to state 1
|
|
|
|
|
|
|
|
exp go to state 9
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
state 6
|
|
|
|
|
|
|
|
exp -> exp '/' . exp (rule 4)
|
|
|
|
|
|
|
|
NUM shift, and go to state 1
|
|
|
|
|
|
|
|
exp go to state 10
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
As was announced in beginning of the report, @samp{State 7 contains 1
|
|
|
|
shift/reduce conflict.}:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 7
|
|
|
|
|
|
|
|
exp -> exp . '+' exp (rule 1)
|
|
|
|
exp -> exp '+' exp . (rule 1)
|
|
|
|
exp -> exp . '-' exp (rule 2)
|
|
|
|
exp -> exp . '*' exp (rule 3)
|
|
|
|
exp -> exp . '/' exp (rule 4)
|
|
|
|
|
|
|
|
'*' shift, and go to state 5
|
|
|
|
'/' shift, and go to state 6
|
|
|
|
|
|
|
|
'/' [reduce using rule 1 (exp)]
|
|
|
|
$default reduce using rule 1 (exp)
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
Indeed, there are two actions associated to the lookahead @samp{/}:
|
|
|
|
either shifting (and going to state 6), or reducing rule 1. The
|
|
|
|
conflict means that either the grammar is ambiguous, or the parser
|
|
|
|
lacks information to make the right decision. Indeed the grammar is
|
|
|
|
ambiguous, as, since we did not specify the precedence of @samp{/},
|
|
|
|
the sentence @samp{NUM + NUM / NUM} can be parsed as @samp{NUM + (NUM
|
|
|
|
/ NUM)}, which corresponds to shifting @samp{/}, or as @samp{(NUM +
|
|
|
|
NUM) / NUM}, which corresponds to reducing rule 1.
|
|
|
|
|
|
|
|
Because in @acronym{LALR(1)} parsing a single decision can be made,
|
|
|
|
Wisent arbitrarily chose to disable the reduction, see
|
|
|
|
@ref{Conflicts}. Discarded actions are reported in between square
|
|
|
|
brackets.
|
|
|
|
|
|
|
|
Note that all the previous states had a single possible action: either
|
|
|
|
shifting the next token and going to the corresponding state, or
|
|
|
|
reducing a single rule. In the other cases, i.e., when shifting
|
|
|
|
@emph{and} reducing is possible or when @emph{several} reductions are
|
|
|
|
possible, the lookahead is required to select the action. State 7 is
|
|
|
|
one such state: if the lookahead is @samp{*} or @samp{/} then the
|
|
|
|
action is shifting, otherwise the action is reducing rule 1. In other
|
|
|
|
words, the first two items, corresponding to rule 1, are not eligible
|
|
|
|
when the lookahead is @samp{*}, since we specified that @samp{*} has
|
|
|
|
higher precedence that @samp{+}. More generally, some items are
|
|
|
|
eligible only with some set of possible lookaheads.
|
|
|
|
|
|
|
|
States 8 to 10 are similar:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 8
|
|
|
|
|
|
|
|
exp -> exp . '+' exp (rule 1)
|
|
|
|
exp -> exp . '-' exp (rule 2)
|
|
|
|
exp -> exp '-' exp . (rule 2)
|
|
|
|
exp -> exp . '*' exp (rule 3)
|
|
|
|
exp -> exp . '/' exp (rule 4)
|
|
|
|
|
|
|
|
'*' shift, and go to state 5
|
|
|
|
'/' shift, and go to state 6
|
|
|
|
|
|
|
|
'/' [reduce using rule 2 (exp)]
|
|
|
|
$default reduce using rule 2 (exp)
|
|
|
|
|
|
|
|
|
|
|
|
state 9
|
|
|
|
|
|
|
|
exp -> exp . '+' exp (rule 1)
|
|
|
|
exp -> exp . '-' exp (rule 2)
|
|
|
|
exp -> exp . '*' exp (rule 3)
|
|
|
|
exp -> exp '*' exp . (rule 3)
|
|
|
|
exp -> exp . '/' exp (rule 4)
|
|
|
|
|
|
|
|
'/' shift, and go to state 6
|
|
|
|
|
|
|
|
'/' [reduce using rule 3 (exp)]
|
|
|
|
$default reduce using rule 3 (exp)
|
|
|
|
|
|
|
|
|
|
|
|
state 10
|
|
|
|
|
|
|
|
exp -> exp . '+' exp (rule 1)
|
|
|
|
exp -> exp . '-' exp (rule 2)
|
|
|
|
exp -> exp . '*' exp (rule 3)
|
|
|
|
exp -> exp . '/' exp (rule 4)
|
|
|
|
exp -> exp '/' exp . (rule 4)
|
|
|
|
|
|
|
|
'+' shift, and go to state 3
|
|
|
|
'-' shift, and go to state 4
|
|
|
|
'*' shift, and go to state 5
|
|
|
|
'/' shift, and go to state 6
|
|
|
|
|
|
|
|
'+' [reduce using rule 4 (exp)]
|
|
|
|
'-' [reduce using rule 4 (exp)]
|
|
|
|
'*' [reduce using rule 4 (exp)]
|
|
|
|
'/' [reduce using rule 4 (exp)]
|
|
|
|
$default reduce using rule 4 (exp)
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
Observe that state 10 contains conflicts due to the lack of precedence
|
|
|
|
of @samp{/} wrt @samp{+}, @samp{-}, and @samp{*}, but also because the
|
|
|
|
associativity of @samp{/} is not specified.
|
|
|
|
|
|
|
|
Finally, the state 11 (plus 12) is named the @dfn{final state}, or the
|
|
|
|
@dfn{accepting state}:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
state 11
|
|
|
|
|
|
|
|
$EOI shift, and go to state 12
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
state 12
|
|
|
|
|
|
|
|
$default accept
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The end of input is shifted @samp{$EOI shift,} and the parser exits
|
|
|
|
successfully (@samp{go to state 12}, that terminates).
|
|
|
|
|
|
|
|
@node Wisent Parsing
|
|
|
|
@chapter Wisent Parsing
|
|
|
|
|
|
|
|
@cindex bottom-up parser
|
|
|
|
@cindex shift-reduce parser
|
|
|
|
The Wisent's parser is what is called a @dfn{bottom-up} or
|
|
|
|
@dfn{shift-reduce} parser which repeatedly:
|
|
|
|
|
|
|
|
@table @dfn
|
|
|
|
@cindex shift
|
|
|
|
@item shift
|
|
|
|
That is pushes the value of the last lexical token read (the
|
|
|
|
look-ahead token) into a value stack, and reads a new one.
|
|
|
|
|
|
|
|
@cindex reduce
|
|
|
|
@item reduce
|
|
|
|
That is replaces a nonterminal by its semantic value. The values of
|
|
|
|
the components which form the right hand side of a rule are popped
|
|
|
|
from the value stack and reduced by the semantic action of this rule.
|
|
|
|
The result is pushed back on top of value stack.
|
|
|
|
@end table
|
|
|
|
|
|
|
|
The parser will stop on:
|
|
|
|
|
|
|
|
@table @dfn
|
|
|
|
@cindex accept
|
|
|
|
@item accept
|
|
|
|
When all input has been successfully parsed. The semantic value of
|
|
|
|
the start nonterminal is on top of the value stack.
|
|
|
|
|
|
|
|
@cindex syntax error
|
|
|
|
@item error
|
|
|
|
When a syntax error (an unexpected token in input) has been detected.
|
|
|
|
At this point the parser issues an error message and either stops or
|
|
|
|
calls a recovery routine to try to resume parsing.
|
|
|
|
@end table
|
|
|
|
|
|
|
|
@cindex table-driven parser
|
|
|
|
The above elementary actions are driven by the @acronym{LALR(1)}
|
|
|
|
automaton built by @code{wisent-compile-grammar} from a context-free
|
|
|
|
grammar.
|
|
|
|
|
|
|
|
The Wisent's parser is entered by calling the function:
|
|
|
|
|
|
|
|
@findex wisent-parse
|
|
|
|
@defun wisent-parse automaton lexer &optional error start
|
|
|
|
Parse input using the automaton specified in @var{automaton}.
|
|
|
|
|
|
|
|
@table @var
|
|
|
|
@item automaton
|
|
|
|
Is an @acronym{LALR(1)} automaton generated by
|
|
|
|
@code{wisent-compile-grammar} (@pxref{Wisent Grammar}).
|
|
|
|
|
|
|
|
@item lexer
|
|
|
|
Is a function with no argument called by the parser to obtain the next
|
|
|
|
terminal (token) in input (@pxref{Writing a lexer}).
|
|
|
|
|
|
|
|
@item error
|
|
|
|
Is an optional reporting function called when a parse error occurs.
|
|
|
|
It receives a message string to report. It defaults to the function
|
|
|
|
@code{wisent-message} (@pxref{Report errors}).
|
|
|
|
|
|
|
|
@item start
|
|
|
|
Specify the start symbol (nonterminal) used by the parser as its goal.
|
|
|
|
It defaults to the start symbol defined in the grammar
|
|
|
|
(@pxref{Wisent Grammar}).
|
|
|
|
@end table
|
|
|
|
@end defun
|
|
|
|
|
2016-01-24 20:30:39 +00:00
|
|
|
The following two normal hooks permit doing some useful processing
|
|
|
|
respectively before starting parsing, and after the parser terminated.
|
2012-12-13 04:44:07 +00:00
|
|
|
|
|
|
|
@vindex wisent-pre-parse-hook
|
|
|
|
@defvar wisent-pre-parse-hook
|
|
|
|
Normal hook run just before entering the @var{LR} parser engine.
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@vindex wisent-post-parse-hook
|
|
|
|
@defvar wisent-post-parse-hook
|
|
|
|
Normal hook run just after the @var{LR} parser engine terminated.
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@menu
|
2012-12-13 04:47:14 +00:00
|
|
|
* Writing a lexer::
|
|
|
|
* Actions goodies::
|
|
|
|
* Report errors::
|
|
|
|
* Error recovery::
|
|
|
|
* Debugging actions::
|
2012-12-13 04:44:07 +00:00
|
|
|
@end menu
|
|
|
|
|
|
|
|
@node Writing a lexer
|
|
|
|
@section What the parser must receive
|
|
|
|
|
|
|
|
It is important to understand that the parser does not parse
|
|
|
|
characters, but lexical tokens, and does not know anything about
|
|
|
|
characters in text streams!
|
|
|
|
|
|
|
|
@cindex lexical analysis
|
|
|
|
@cindex lexer
|
|
|
|
@cindex scanner
|
|
|
|
Reading input data to produce lexical tokens is performed by a lexer
|
|
|
|
(also called a scanner) in a lexical analysis step, before the syntax
|
|
|
|
analysis step performed by the parser. The parser automatically calls
|
|
|
|
the lexer when it needs the next token to parse.
|
|
|
|
|
|
|
|
@cindex lexical tokens
|
|
|
|
A Wisent's lexer is an Emacs Lisp function with no argument. It must
|
|
|
|
return a valid lexical token of the form:
|
|
|
|
|
|
|
|
@code{(@var{token-class value} [@var{start} . @var{end}])}
|
|
|
|
|
|
|
|
@table @var
|
|
|
|
@item token-class
|
|
|
|
Is a category of lexical token identifying a terminal as specified in
|
|
|
|
the grammar (@pxref{Wisent Grammar}). It can be a symbol or a character
|
|
|
|
literal.
|
|
|
|
|
|
|
|
@item value
|
|
|
|
Is the value of the lexical token. It can be of any valid Emacs Lisp
|
|
|
|
data type.
|
|
|
|
|
|
|
|
@item start
|
|
|
|
@itemx end
|
2012-12-14 20:05:03 +00:00
|
|
|
Are the optional beginning and ending positions of @var{value} in the
|
2012-12-13 04:44:07 +00:00
|
|
|
input stream.
|
|
|
|
@end table
|
|
|
|
|
|
|
|
When there are no more tokens to read the lexer must return the token
|
|
|
|
@code{(list wisent-eoi-term)} to each request.
|
|
|
|
|
|
|
|
@vindex wisent-eoi-term
|
|
|
|
@defvar wisent-eoi-term
|
|
|
|
Predefined constant, End-Of-Input terminal symbol.
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@code{wisent-lex} is an example of a lexer that reads lexical tokens
|
|
|
|
produced by a @semantic{} lexer, and translates them into lexical tokens
|
|
|
|
suitable to the Wisent parser. See also @ref{Wisent Lex}.
|
|
|
|
|
|
|
|
To call the lexer in a semantic action use the function
|
|
|
|
@code{wisent-lexer}. See also @ref{Actions goodies}.
|
|
|
|
|
|
|
|
@node Actions goodies
|
|
|
|
@section Variables and macros useful in grammar actions.
|
|
|
|
|
|
|
|
@vindex wisent-input
|
|
|
|
@defvar wisent-input
|
|
|
|
The last token read.
|
|
|
|
This variable only has meaning in the scope of @code{wisent-parse}.
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@findex wisent-lexer
|
|
|
|
@defun wisent-lexer
|
|
|
|
Obtain the next terminal in input.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@findex wisent-region
|
|
|
|
@defun wisent-region &rest positions
|
|
|
|
Return the start/end positions of the region including
|
|
|
|
@var{positions}. Each element of @var{positions} is a pair
|
|
|
|
@w{@code{(@var{start-pos} . @var{end-pos})}} or @code{nil}. The
|
|
|
|
returned value is the pair @w{@code{(@var{min-start-pos} .
|
|
|
|
@var{max-end-pos})}} or @code{nil} if no @var{positions} are
|
|
|
|
available.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@node Report errors
|
|
|
|
@section The error reporting function
|
|
|
|
|
|
|
|
@cindex error reporting
|
|
|
|
When the parser encounters a syntax error it calls a user-defined
|
|
|
|
function. It must be an Emacs Lisp function with one argument: a
|
|
|
|
string containing the message to report.
|
|
|
|
|
|
|
|
By default the parser uses this function to report error messages:
|
|
|
|
|
|
|
|
@findex wisent-message
|
|
|
|
@defun wisent-message string &rest args
|
|
|
|
Print a one-line message if @code{wisent-parse-verbose-flag} is set.
|
|
|
|
Pass @var{string} and @var{args} arguments to @dfn{message}.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@table @strong
|
|
|
|
@item Please Note:
|
|
|
|
@code{wisent-message} uses the following function to print lexical
|
|
|
|
tokens:
|
|
|
|
|
|
|
|
@defun wisent-token-to-string token
|
|
|
|
Return a printed representation of lexical token @var{token}.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
The general printed form of a lexical token is:
|
|
|
|
|
|
|
|
@w{@code{@var{token}(@var{value})@@@var{location}}}
|
|
|
|
@end table
|
|
|
|
|
|
|
|
To control the verbosity of the parser you can set to non-@code{nil}
|
|
|
|
this variable:
|
|
|
|
|
|
|
|
@vindex wisent-parse-verbose-flag
|
|
|
|
@deffn Option wisent-parse-verbose-flag
|
|
|
|
non-@code{nil} means to issue more messages while parsing.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
Or interactively use the command:
|
|
|
|
|
|
|
|
@findex wisent-parse-toggle-verbose-flag
|
|
|
|
@deffn Command wisent-parse-toggle-verbose-flag
|
|
|
|
Toggle whether to issue more messages while parsing.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
When the error reporting function is entered the variable
|
|
|
|
@code{wisent-input} contains the unexpected token as returned by the
|
|
|
|
lexer.
|
|
|
|
|
|
|
|
The error reporting function can be called from a semantic action too
|
|
|
|
using the special macro @code{wisent-error}. When called from a
|
|
|
|
semantic action entered by error recovery (@pxref{Error recovery}) the
|
|
|
|
value of the variable @code{wisent-recovering} is non-@code{nil}.
|
|
|
|
|
|
|
|
@node Error recovery
|
|
|
|
@section Error recovery
|
|
|
|
|
|
|
|
@cindex error recovery
|
|
|
|
The error recovery mechanism of the Wisent's parser conforms to the
|
|
|
|
one Bison uses. See @ref{Error Recovery, , , bison}, in the Bison
|
|
|
|
manual for details.
|
|
|
|
|
|
|
|
@cindex error token
|
|
|
|
To recover from a syntax error you must write rules to recognize the
|
|
|
|
special token @code{error}. This is a terminal symbol that is
|
|
|
|
automatically defined and reserved for error handling.
|
|
|
|
|
|
|
|
When the parser encounters a syntax error, it pops the state stack
|
|
|
|
until it finds a state that allows shifting the @code{error} token.
|
|
|
|
After it has been shifted, if the old look-ahead token is not
|
|
|
|
acceptable to be shifted next, the parser reads tokens and discards
|
|
|
|
them until it finds a token which is acceptable.
|
|
|
|
|
|
|
|
@cindex error recovery strategy
|
|
|
|
Strategies for error recovery depend on the choice of error rules in
|
|
|
|
the grammar. A simple and useful strategy is simply to skip the rest
|
|
|
|
of the current statement if an error is detected:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
2012-12-14 20:05:03 +00:00
|
|
|
(statement (( error ?; )) ;; on error, skip until ';' is read
|
|
|
|
)
|
2012-12-13 04:44:07 +00:00
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
It is also useful to recover to the matching close-delimiter of an
|
|
|
|
opening-delimiter that has already been parsed:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
(primary (( ?@{ expr ?@} ))
|
|
|
|
(( ?@{ error ?@} ))
|
|
|
|
@dots{}
|
|
|
|
)
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
@cindex error recovery actions
|
|
|
|
Note that error recovery rules may have actions, just as any other
|
|
|
|
rules can. Here are some predefined hooks, variables, functions or
|
|
|
|
macros, useful in such actions:
|
|
|
|
|
|
|
|
@vindex wisent-nerrs
|
|
|
|
@defvar wisent-nerrs
|
|
|
|
The number of parse errors encountered so far.
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@vindex wisent-recovering
|
|
|
|
@defvar wisent-recovering
|
|
|
|
non-@code{nil} means that the parser is recovering.
|
|
|
|
This variable only has meaning in the scope of @code{wisent-parse}.
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@findex wisent-error
|
|
|
|
@defun wisent-error msg
|
|
|
|
Call the user supplied error reporting function with message
|
|
|
|
@var{msg} (@pxref{Report errors}).
|
|
|
|
|
|
|
|
For an example of use, @xref{wisent-skip-token}.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@findex wisent-errok
|
|
|
|
@defun wisent-errok
|
|
|
|
Resume generating error messages immediately for subsequent syntax
|
|
|
|
errors.
|
|
|
|
|
|
|
|
The parser suppress error message for syntax errors that happens
|
|
|
|
shortly after the first, until three consecutive input tokens have
|
|
|
|
been successfully shifted.
|
|
|
|
|
|
|
|
Calling @code{wisent-errok} in an action, make error messages resume
|
|
|
|
immediately. No error messages will be suppressed if you call it in
|
|
|
|
an error rule's action.
|
|
|
|
|
|
|
|
For an example of use, @xref{wisent-skip-token}.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@findex wisent-clearin
|
|
|
|
@defun wisent-clearin
|
|
|
|
Discard the current lookahead token.
|
|
|
|
This will cause a new lexical token to be read.
|
|
|
|
|
|
|
|
In an error rule's action the previous lookahead token is reanalyzed
|
|
|
|
immediately. @code{wisent-clearin} may be called to clear this token.
|
|
|
|
|
|
|
|
For example, suppose that on a parse error, an error handling routine
|
|
|
|
is called that advances the input stream to some point where parsing
|
|
|
|
should once again commence. The next symbol returned by the lexical
|
|
|
|
scanner is probably correct. The previous lookahead token ought to
|
|
|
|
be discarded with @code{wisent-clearin}.
|
|
|
|
|
|
|
|
For an example of use, @xref{wisent-skip-token}.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@findex wisent-abort
|
|
|
|
@defun wisent-abort
|
|
|
|
Abort parsing and save the lookahead token.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@findex wisent-set-region
|
|
|
|
@defun wisent-set-region start end
|
|
|
|
Change the region of text matched by the current nonterminal.
|
|
|
|
@var{start} and @var{end} are respectively the beginning and end
|
|
|
|
positions of the region occupied by the group of components associated
|
|
|
|
to this nonterminal. If @var{start} or @var{end} values are not a
|
|
|
|
valid positions the region is set to @code{nil}.
|
|
|
|
|
|
|
|
For an example of use, @xref{wisent-skip-token}.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@vindex wisent-discarding-token-functions
|
|
|
|
@defvar wisent-discarding-token-functions
|
|
|
|
List of functions to be called when discarding a lexical token.
|
|
|
|
These functions receive the lexical token discarded.
|
|
|
|
When the parser encounters unexpected tokens, it can discards them,
|
|
|
|
based on what directed by error recovery rules. Either when the
|
|
|
|
parser reads tokens until one is found that can be shifted, or when an
|
|
|
|
semantic action calls the function @code{wisent-skip-token} or
|
|
|
|
@code{wisent-skip-block}.
|
|
|
|
For language specific hooks, make sure you define this as a local
|
|
|
|
hook.
|
|
|
|
|
|
|
|
For example, in @semantic{}, this hook is set to the function
|
|
|
|
@code{wisent-collect-unmatched-syntax} to collect unmatched lexical
|
|
|
|
tokens (@pxref{Useful functions}).
|
|
|
|
@end defvar
|
|
|
|
|
|
|
|
@findex wisent-skip-token
|
|
|
|
@defun wisent-skip-token
|
|
|
|
@anchor{wisent-skip-token}
|
|
|
|
Skip the lookahead token in order to resume parsing.
|
2014-06-08 23:39:23 +00:00
|
|
|
Return @code{nil}.
|
2012-12-13 04:44:07 +00:00
|
|
|
Must be used in error recovery semantic actions.
|
|
|
|
|
|
|
|
It typically looks like this:
|
|
|
|
|
|
|
|
@lisp
|
|
|
|
@group
|
|
|
|
(wisent-message "%s: skip %s" $action
|
|
|
|
(wisent-token-to-string wisent-input))
|
|
|
|
(run-hook-with-args
|
|
|
|
'wisent-discarding-token-functions wisent-input)
|
|
|
|
(wisent-clearin)
|
|
|
|
(wisent-errok)))
|
|
|
|
@end group
|
|
|
|
@end lisp
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@findex wisent-skip-block
|
|
|
|
@defun wisent-skip-block
|
|
|
|
Safely skip a block in order to resume parsing.
|
2014-06-08 23:39:23 +00:00
|
|
|
Return @code{nil}.
|
2012-12-13 04:44:07 +00:00
|
|
|
Must be used in error recovery semantic actions.
|
|
|
|
|
|
|
|
A block is data between an open-delimiter (syntax class @code{(}) and
|
|
|
|
a matching close-delimiter (syntax class @code{)}):
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
(a parenthesized block)
|
|
|
|
[a block between brackets]
|
|
|
|
@{a block between braces@}
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The following example uses @code{wisent-skip-block} to safely skip a
|
|
|
|
block delimited by @samp{LBRACE} (@code{@{}) and @samp{RBRACE}
|
|
|
|
(@code{@}}) tokens, when a syntax error occurs in
|
|
|
|
@samp{other-components}:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
(block ((LBRACE other-components RBRACE))
|
|
|
|
((LBRACE RBRACE))
|
|
|
|
((LBRACE error)
|
|
|
|
(wisent-skip-block))
|
|
|
|
)
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@node Debugging actions
|
|
|
|
@section Debugging semantic actions
|
|
|
|
|
|
|
|
@cindex semantic action symbols
|
|
|
|
Each semantic action is represented by a symbol interned in an
|
|
|
|
@dfn{obarray} that is part of the @acronym{LALR(1)} automaton
|
|
|
|
(@pxref{Compiling a grammar}). @code{symbol-function} on a semantic
|
|
|
|
action symbol return the semantic action lambda expression.
|
|
|
|
|
|
|
|
A semantic action symbol name has the form
|
|
|
|
@code{@var{nonterminal}:@var{index}}, where @var{nonterminal} is the
|
|
|
|
name of the nonterminal symbol the action belongs to, and @var{index}
|
|
|
|
is an action sequence number within the scope of @var{nonterminal}.
|
|
|
|
For example, this nonterminal definition:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
input:
|
|
|
|
line [@code{input:0}]
|
|
|
|
| input line
|
|
|
|
(format "%s %s" $1 $2) [@code{input:1}]
|
|
|
|
;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
Will produce two semantic actions, and associated symbols:
|
|
|
|
|
|
|
|
@table @code
|
|
|
|
@item input:0
|
|
|
|
A default action that returns @code{$1}.
|
|
|
|
|
|
|
|
@item input:1
|
|
|
|
That returns @code{(format "%s %s" $1 $2)}.
|
|
|
|
@end table
|
|
|
|
|
|
|
|
@cindex debugging semantic actions
|
|
|
|
Debugging uses the Lisp debugger to investigate what is happening
|
|
|
|
during execution of semantic actions.
|
|
|
|
Three commands are available to debug semantic actions. They receive
|
|
|
|
two arguments:
|
|
|
|
|
|
|
|
@itemize @bullet
|
|
|
|
@item The automaton that contains the semantic action.
|
|
|
|
|
|
|
|
@item The semantic action symbol.
|
|
|
|
@end itemize
|
|
|
|
|
|
|
|
@findex wisent-debug-on-entry
|
|
|
|
@deffn Command wisent-debug-on-entry automaton function
|
|
|
|
Request @var{automaton}'s @var{function} to invoke debugger each time it is called.
|
|
|
|
@var{function} must be a semantic action symbol that exists in @var{automaton}.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
@findex wisent-cancel-debug-on-entry
|
|
|
|
@deffn Command wisent-cancel-debug-on-entry automaton function
|
|
|
|
Undo effect of @code{wisent-debug-on-entry} on @var{automaton}'s @var{function}.
|
|
|
|
@var{function} must be a semantic action symbol that exists in @var{automaton}.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
@findex wisent-debug-show-entry
|
|
|
|
@deffn Command wisent-debug-show-entry automaton function
|
|
|
|
Show the source of @var{automaton}'s semantic action @var{function}.
|
|
|
|
@var{function} must be a semantic action symbol that exists in @var{automaton}.
|
|
|
|
@end deffn
|
|
|
|
|
|
|
|
@node Wisent Semantic
|
|
|
|
@chapter How to use Wisent with Semantic
|
|
|
|
|
|
|
|
@cindex tags
|
|
|
|
This section presents how the Wisent's parser can be used to produce
|
|
|
|
@dfn{tags} for the @semantic{} tool set.
|
|
|
|
|
|
|
|
@semantic{} tags form a hierarchy of Emacs Lisp data structures that
|
|
|
|
describes a program in a way independent of programming languages.
|
|
|
|
Tags map program declarations, like functions, methods, variables,
|
|
|
|
data types, classes, includes, grammar rules, etc..
|
|
|
|
|
|
|
|
@cindex WY grammar format
|
|
|
|
To use the Wisent parser with @semantic{} you have to define
|
|
|
|
your grammar in @dfn{WY} form, a grammar format very close
|
|
|
|
to the one used by Bison.
|
|
|
|
|
|
|
|
Please @inforef{top, Semantic Grammar Framework Manual, grammar-fw}
|
|
|
|
for more information on @semantic{} grammars.
|
|
|
|
|
|
|
|
@menu
|
2012-12-13 04:47:14 +00:00
|
|
|
* Grammar styles::
|
|
|
|
* Wisent Lex::
|
2012-12-13 04:44:07 +00:00
|
|
|
@end menu
|
|
|
|
|
|
|
|
@node Grammar styles
|
|
|
|
@section Grammar styles
|
|
|
|
|
|
|
|
@cindex grammar styles
|
|
|
|
@semantic{} parsing heavily depends on how you wrote the grammar.
|
|
|
|
There are mainly two styles to write a Wisent's grammar intended to be
|
|
|
|
used with the @semantic{} tool set: the @dfn{Iterative style} and the
|
|
|
|
@dfn{Bison style}. Each one has pros and cons, and in certain cases
|
|
|
|
it can be worth a mix of the two styles!
|
|
|
|
|
|
|
|
@menu
|
2012-12-13 04:47:14 +00:00
|
|
|
* Iterative style::
|
|
|
|
* Bison style::
|
|
|
|
* Mixed style::
|
|
|
|
* Start nonterminals::
|
|
|
|
* Useful functions::
|
2012-12-13 04:44:07 +00:00
|
|
|
@end menu
|
|
|
|
|
2012-12-22 20:19:41 +00:00
|
|
|
@node Iterative style
|
2012-12-13 04:44:07 +00:00
|
|
|
@subsection Iterative style
|
|
|
|
|
|
|
|
@cindex grammar iterative style
|
|
|
|
The @dfn{iterative style} is the preferred style to use with @semantic{}.
|
|
|
|
It relies on an iterative parser back-end mechanism which parses start
|
|
|
|
nonterminals one at a time and automagically skips unexpected lexical
|
|
|
|
tokens in input.
|
|
|
|
|
|
|
|
Compared to rule-based iterative functions (@pxref{Bison style}),
|
|
|
|
iterative parsers are better in that they can handle obscure errors
|
|
|
|
more cleanly.
|
|
|
|
|
|
|
|
@cindex raw tag
|
|
|
|
Each start nonterminal must produces a @dfn{raw tag} by calling a
|
|
|
|
@code{TAG}-like grammar macro with appropriate parameters. See also
|
|
|
|
@ref{Start nonterminals}.
|
|
|
|
|
|
|
|
@cindex expanded tag
|
|
|
|
Then, each parsing iteration automatically translates a raw tag into
|
|
|
|
@dfn{expanded tags}, updating the raw tag structure with internal
|
|
|
|
properties and buffer related data.
|
|
|
|
|
|
|
|
After parsing completes, it results in a tree of expanded tags.
|
|
|
|
|
|
|
|
The following example is a snippet of the iterative style Java grammar
|
|
|
|
provided in the @semantic{} distribution in the file
|
|
|
|
@file{semantic/wisent/java-tags.wy}.
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
@dots{}
|
|
|
|
;; Alternate entry points
|
|
|
|
;; - Needed by partial re-parse
|
|
|
|
%start formal_parameter
|
|
|
|
@dots{}
|
|
|
|
;; - Needed by EXPANDFULL clauses
|
|
|
|
%start formal_parameters
|
|
|
|
@dots{}
|
|
|
|
|
|
|
|
formal_parameter_list
|
|
|
|
: PAREN_BLOCK
|
|
|
|
(EXPANDFULL $1 formal_parameters)
|
|
|
|
;
|
|
|
|
|
|
|
|
formal_parameters
|
|
|
|
: LPAREN
|
|
|
|
()
|
|
|
|
| RPAREN
|
|
|
|
()
|
|
|
|
| formal_parameter COMMA
|
|
|
|
| formal_parameter RPAREN
|
|
|
|
;
|
|
|
|
|
|
|
|
formal_parameter
|
|
|
|
: formal_parameter_modifier_opt type variable_declarator_id
|
|
|
|
(VARIABLE-TAG $3 $2 nil :typemodifiers $1)
|
|
|
|
;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
@findex EXPANDFULL
|
|
|
|
It shows the use of the @code{EXPANDFULL} grammar macro to parse a
|
|
|
|
@samp{PAREN_BLOCK} which contains a @samp{formal_parameter_list}.
|
|
|
|
@code{EXPANDFULL} tells to recursively parse @samp{formal_parameters}
|
|
|
|
inside @samp{PAREN_BLOCK}. The parser iterates until it digested all
|
|
|
|
available input data inside the @samp{PAREN_BLOCK}, trying to match
|
|
|
|
any of the @samp{formal_parameters} rules:
|
|
|
|
|
|
|
|
@itemize
|
|
|
|
@item @samp{LPAREN}
|
|
|
|
|
|
|
|
@item @samp{RPAREN}
|
|
|
|
|
|
|
|
@item @samp{formal_parameter COMMA}
|
|
|
|
|
|
|
|
@item @samp{formal_parameter RPAREN}
|
|
|
|
@end itemize
|
|
|
|
|
|
|
|
At each iteration it will return a @samp{formal_parameter} raw tag,
|
|
|
|
or @code{nil} to skip unwanted (single @samp{LPAREN} or @samp{RPAREN}
|
|
|
|
for example) or unexpected input data. Those raw tags will be
|
|
|
|
automatically expanded by the iterative back-end parser.
|
|
|
|
|
|
|
|
@node Bison style
|
|
|
|
@subsection Bison style
|
|
|
|
|
|
|
|
@cindex grammar bison style
|
|
|
|
What we call the @dfn{Bison style} is the traditional style of Bison's
|
|
|
|
grammars. Compared to iterative style, it is not straightforward to
|
|
|
|
use grammars written in Bison style in @semantic{}. Mainly because such
|
|
|
|
grammars are designed to parse the whole input data in one pass, and
|
|
|
|
don't use the iterative parser back-end mechanism (@pxref{Iterative
|
|
|
|
style}). With Bison style the parser is called once to parse the
|
|
|
|
grammar start nonterminal.
|
|
|
|
|
|
|
|
The following example is a snippet of the Bison style Java grammar
|
|
|
|
provided in the @semantic{} distribution in the file
|
|
|
|
@file{semantic/wisent/java.wy}.
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
%start formal_parameter
|
|
|
|
@dots{}
|
|
|
|
|
|
|
|
formal_parameter_list
|
|
|
|
: formal_parameter_list COMMA formal_parameter
|
|
|
|
(cons $3 $1)
|
|
|
|
| formal_parameter
|
|
|
|
(list $1)
|
|
|
|
;
|
|
|
|
|
|
|
|
formal_parameter
|
|
|
|
: formal_parameter_modifier_opt type variable_declarator_id
|
|
|
|
(EXPANDTAG
|
|
|
|
(VARIABLE-TAG $3 $2 :typemodifiers $1)
|
|
|
|
)
|
|
|
|
;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The first consequence is that syntax errors are not automatically
|
|
|
|
handled by @semantic{}. Thus, it is necessary to explicitly handle
|
|
|
|
them at the grammar level, providing error recovery rules to skip
|
|
|
|
unexpected input data.
|
|
|
|
|
|
|
|
The second consequence is that the iterative parser can't do automatic
|
|
|
|
tag expansion, except for the start nonterminal value. It is
|
|
|
|
necessary to explicitly expand tags from concerned semantic actions by
|
|
|
|
calling the grammar macro @code{EXPANDTAG} with a raw tag as
|
|
|
|
parameter. See also @ref{Start nonterminals}, for incremental
|
|
|
|
re-parse considerations.
|
|
|
|
|
|
|
|
@node Mixed style
|
|
|
|
@subsection Mixed style
|
|
|
|
|
|
|
|
@cindex grammar mixed style
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
%start grammar
|
|
|
|
;; Reparse
|
|
|
|
%start prologue epilogue declaration nonterminal rule
|
|
|
|
@dots{}
|
|
|
|
|
|
|
|
%%
|
|
|
|
|
|
|
|
grammar:
|
|
|
|
prologue
|
|
|
|
| epilogue
|
|
|
|
| declaration
|
|
|
|
| nonterminal
|
|
|
|
| PERCENT_PERCENT
|
|
|
|
;
|
|
|
|
@dots{}
|
|
|
|
|
|
|
|
nonterminal:
|
|
|
|
SYMBOL COLON rules SEMI
|
|
|
|
(TAG $1 'nonterminal :children $3)
|
|
|
|
;
|
|
|
|
|
|
|
|
rules:
|
|
|
|
lifo_rules
|
|
|
|
(apply 'nconc (nreverse $1))
|
|
|
|
;
|
|
|
|
|
|
|
|
lifo_rules:
|
|
|
|
lifo_rules OR rule
|
|
|
|
(cons $3 $1)
|
|
|
|
| rule
|
|
|
|
(list $1)
|
|
|
|
;
|
|
|
|
|
|
|
|
rule:
|
|
|
|
rhs
|
|
|
|
(let* ((rhs $1)
|
|
|
|
name type comps prec action elt)
|
|
|
|
@dots{}
|
|
|
|
(EXPANDTAG
|
|
|
|
(TAG name 'rule :type type :value comps :prec prec :expr action)
|
|
|
|
))
|
|
|
|
;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
This example shows how iterative and Bison styles can be combined in
|
|
|
|
the same grammar to obtain a good compromise between grammar
|
|
|
|
complexity and an efficient parsing strategy in an interactive
|
|
|
|
environment.
|
|
|
|
|
|
|
|
@samp{nonterminal} is parsed using iterative style via the main
|
|
|
|
@samp{grammar} rule. The semantic action uses the @code{TAG} macro to
|
|
|
|
produce a raw tag, automagically expanded by @semantic{}.
|
|
|
|
|
|
|
|
But @samp{rules} part is parsed in Bison style! Why?
|
|
|
|
|
|
|
|
Rule delimiters are the colon (@code{:}), that follows the nonterminal
|
|
|
|
name, and a final semicolon (@code{;}). Unfortunately these
|
|
|
|
delimiters are not @code{open-paren}/@code{close-paren} type, and the
|
|
|
|
Emacs' syntactic analyzer can't easily isolate data between them to
|
|
|
|
produce a @samp{RULES_PART} parenthesis-block-like lexical token.
|
|
|
|
Consequently it is not possible to use @code{EXPANDFULL} to iterate in
|
|
|
|
@samp{RULES_PART}, like this:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
nonterminal:
|
|
|
|
SYMBOL COLON rules SEMI
|
|
|
|
(TAG $1 'nonterminal :children $3)
|
|
|
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;
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rules:
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RULES_PART ;; @strong{Map a parenthesis-block-like lexical token}
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|
(EXPANDFULL $1 'rules)
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;
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rules:
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|
COLON
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|
()
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|
OR
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|
()
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|
|
SEMI
|
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|
()
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|
rhs
|
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|
rhs
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|
(let* ((rhs $1)
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|
|
name type comps prec action elt)
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|
@dots{}
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(TAG name 'rule :type type :value comps :prec prec :expr action)
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)
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;
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|
@end group
|
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|
@end example
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|
|
|
In such cases, when it is difficult for Emacs to obtain
|
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|
|
parenthesis-block-like lexical tokens, the best solution is to use the
|
|
|
|
traditional Bison style with error recovery!
|
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|
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|
|
|
In some extreme cases, it can also be convenient to extend the lexer,
|
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|
|
to deliver new lexical tokens, to simplify the grammar.
|
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|
|
@node Start nonterminals
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|
@subsection Start nonterminals
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|
|
@cindex start nonterminals
|
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|
@cindex @code{reparse-symbol} property
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|
|
When you write a grammar for @semantic{}, it is important to carefully
|
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|
|
indicate the start nonterminals. Each one defines an entry point in
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|
|
the grammar, and after parsing its semantic value is returned to the
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|
|
back-end iterative engine. Consequently:
|
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@strong{The semantic value of a start nonterminal must be a produced
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|
|
by a TAG like grammar macro}.
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|
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Start nonterminals are declared by @code{%start} statements. When
|
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|
|
nothing is specified the first nonterminal that appears in the grammar
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|
|
is the start nonterminal.
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|
|
Generally, the following nonterminals must be declared as start
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|
|
symbols:
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|
|
@itemize @bullet
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|
|
@item The main grammar entry point
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|
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@quotation
|
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|
|
Of course!
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|
|
@end quotation
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|
|
@item nonterminals passed to @code{EXPAND}/@code{EXPANDFULL}
|
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|
|
@quotation
|
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|
|
These grammar macros recursively parse a part of input data, based on
|
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|
|
rules of the given nonterminal.
|
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|
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|
|
For example, the following will parse @samp{PAREN_BLOCK} data using
|
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|
|
the @samp{formal_parameters} rules:
|
|
|
|
|
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|
|
@example
|
|
|
|
@group
|
|
|
|
formal_parameter_list
|
|
|
|
: PAREN_BLOCK
|
|
|
|
(EXPANDFULL $1 formal_parameters)
|
|
|
|
;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
The semantic value of @samp{formal_parameters} becomes the value of
|
|
|
|
the @code{EXPANDFULL} expression. It is a list of @semantic{} tags
|
|
|
|
spliced in the tags tree.
|
|
|
|
|
|
|
|
Because the automaton must know that @samp{formal_parameters} is a
|
|
|
|
start symbol, you must declare it like this:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
%start formal_parameters
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
@end quotation
|
|
|
|
@end itemize
|
|
|
|
|
|
|
|
@cindex incremental re-parse
|
|
|
|
@cindex reparse-symbol
|
|
|
|
The @code{EXPANDFULL} macro has a side effect it is important to know,
|
|
|
|
related to the incremental re-parse mechanism of @semantic{}: the
|
|
|
|
nonterminal symbol parameter passed to @code{EXPANDFULL} also becomes
|
|
|
|
the @code{reparse-symbol} property of the tag returned by the
|
|
|
|
@code{EXPANDFULL} expression.
|
|
|
|
|
|
|
|
When buffer's data mapped by a tag is modified, @semantic{}
|
|
|
|
schedules an incremental re-parse of that data, using the tag's
|
|
|
|
@code{reparse-symbol} property as start nonterminal.
|
|
|
|
|
|
|
|
@strong{The rules associated to such start symbols must be carefully
|
|
|
|
reviewed to ensure that the incremental parser will work!}
|
|
|
|
|
|
|
|
Things are a little bit different when the grammar is written in Bison
|
2012-12-13 04:47:14 +00:00
|
|
|
style.
|
2012-12-13 04:44:07 +00:00
|
|
|
|
|
|
|
@strong{The @code{reparse-symbol} property is set to the nonterminal
|
|
|
|
symbol the rule that explicitly uses @code{EXPANDTAG} belongs to.}
|
|
|
|
|
|
|
|
For example:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
rule:
|
|
|
|
rhs
|
|
|
|
(let* ((rhs $1)
|
|
|
|
name type comps prec action elt)
|
|
|
|
@dots{}
|
|
|
|
(EXPANDTAG
|
|
|
|
(TAG name 'rule :type type :value comps :prec prec :expr action)
|
|
|
|
))
|
|
|
|
;
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
Set the @code{reparse-symbol} property of the expanded tag to
|
|
|
|
@samp{rule}. A important consequence is that:
|
|
|
|
|
|
|
|
@strong{Every nonterminal having any rule that calls @code{EXPANDTAG}
|
|
|
|
in a semantic action, should be declared as a start symbol!}
|
|
|
|
|
|
|
|
@node Useful functions
|
|
|
|
@subsection Useful functions
|
|
|
|
|
|
|
|
Here is a description of some predefined functions it might be useful
|
|
|
|
to know when writing new code to use Wisent in @semantic{}:
|
|
|
|
|
|
|
|
@findex wisent-collect-unmatched-syntax
|
|
|
|
@defun wisent-collect-unmatched-syntax input
|
|
|
|
Add @var{input} lexical token to the cache of unmatched tokens, in
|
|
|
|
variable @code{semantic-unmatched-syntax-cache}.
|
|
|
|
|
|
|
|
See implementation of the function @code{wisent-skip-token} in
|
|
|
|
@ref{Error recovery}, for an example of use.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
@node Wisent Lex
|
|
|
|
@section The Wisent Lex lexer
|
|
|
|
|
|
|
|
@findex semantic-lex
|
|
|
|
The lexical analysis step of @semantic{} is performed by the general
|
|
|
|
function @code{semantic-lex}. For more information, @inforef{Writing
|
|
|
|
Lexers, ,semantic-langdev}.
|
|
|
|
|
|
|
|
@code{semantic-lex} produces lexical tokens of the form:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
@code{(@var{token-class start} . @var{end})}
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
@table @var
|
|
|
|
@item token-class
|
|
|
|
Is a symbol that identifies a lexical token class, like @code{symbol},
|
|
|
|
@code{string}, @code{number}, or @code{PAREN_BLOCK}.
|
|
|
|
|
|
|
|
@item start
|
|
|
|
@itemx end
|
|
|
|
Are the start and end positions of mapped data in the input buffer.
|
|
|
|
@end table
|
2012-12-13 04:47:14 +00:00
|
|
|
|
2012-12-13 04:44:07 +00:00
|
|
|
The Wisent's parser doesn't depend on the nature of analyzed input
|
|
|
|
stream (buffer, string, etc.), and requires that lexical tokens have a
|
|
|
|
different form (@pxref{Writing a lexer}):
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
@code{(@var{token-class value} [@var{start} . @var{end}])}
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
@cindex lexical token mapping
|
|
|
|
@code{wisent-lex} is the default Wisent's lexer used in @semantic{}.
|
|
|
|
|
|
|
|
@vindex wisent-lex-istream
|
|
|
|
@findex wisent-lex
|
|
|
|
@defun wisent-lex
|
|
|
|
Return the next available lexical token in Wisent's form.
|
|
|
|
|
|
|
|
The variable @code{wisent-lex-istream} contains the list of lexical
|
|
|
|
tokens produced by @code{semantic-lex}. Pop the next token available
|
|
|
|
and convert it to a form suitable for the Wisent's parser.
|
|
|
|
@end defun
|
|
|
|
|
|
|
|
Mapping of lexical tokens as produced by @code{semantic-lex} into
|
|
|
|
equivalent Wisent lexical tokens is straightforward:
|
|
|
|
|
|
|
|
@example
|
|
|
|
@group
|
|
|
|
(@var{token-class start} . @var{end})
|
|
|
|
@result{} (@var{token-class value start} . @var{end})
|
|
|
|
@end group
|
|
|
|
@end example
|
|
|
|
|
|
|
|
@var{value} is the input @code{buffer-substring} from @var{start} to
|
|
|
|
@var{end}.
|
|
|
|
|
|
|
|
@node GNU Free Documentation License
|
|
|
|
@appendix GNU Free Documentation License
|
|
|
|
|
2012-12-13 04:47:14 +00:00
|
|
|
@include doclicense.texi
|
2012-12-13 04:44:07 +00:00
|
|
|
|
|
|
|
@node Index
|
|
|
|
@unnumbered Index
|
|
|
|
@printindex cp
|
|
|
|
|
|
|
|
@iftex
|
|
|
|
@contents
|
|
|
|
@summarycontents
|
|
|
|
@end iftex
|
|
|
|
|
|
|
|
@bye
|
|
|
|
|
|
|
|
@c Following comments are for the benefit of ispell.
|
|
|
|
|
|
|
|
@c LocalWords: Wisent automagically wisent Wisent's LALR obarray
|