[PATCH] Document %define lr.type and lr.default_rules.

[Joel E. Denny]

In the manual, the discussion of %define lr.* is getting too verbose for 
Decl Summary.  I should move the details to a new section, but I haven't 
figured out where yet.

Pushed to branch-2.5 and master.

>From 34a6c2d19b85d4650b2d90f60b76d44071d167d1 Mon Sep 17 00:00:00 2001
From: Joel E. Denny <address@hidden>
Date: Tue, 21 Apr 2009 05:12:01 -0400
Subject: [PATCH] Document %define lr.type and lr.default_rules.

* NEWS (2.5): Add an entry.
* src/getargs.c (usage): Mention IELR(1) and canonical LR(1)
besides just LALR(1) and GLR(1).
* doc/bison.texinfo (Introduction): Likewise.
(Language and Grammar): Bison is no longer limited to LALR(1)
restrictions.
(GLR parsing): Say deterministic or LR(1) rather than LALR(1)
when trying to distinguish from GLR.  Talk about LR(1) grammars
rather than LALR(1) grammars.
(Decl Summary): In %define api.push_pull entry, say it applies
to deterministic parsers in C rather than LALR(1) parsers in C.
Add lr.default_rules entry.
Add lr.type entry.
(Mystery Conflicts): Bison is no longer limited to LALR(1)
restrictions.
(Generalized LR Parsing): Same changes as for the previous GLR
section.
(Memory Management): Say deterministic rather than LALR(1).
(Understanding): Correct some bison output.
Index discussion of "accepting state".
Say deterministic rather than LALR(1).
(Bison Options): In --yacc entry, say deterministic rather than
LALR(1).
In --report, --graph, and --xml entries, just don't mention
LALR(1).
(C++ Parsers): Say deterministic rather than LALR(1).
(Table of Symbols): Likewise in YYSTACK_USE_ALLOCA entry.
(Glossary): Add Accepting State, Consistent State, Default Rule,
and IELR(1) definitions.
In Generalized LR (GLR) definition, make same changes as in
previous GLR sections.
In LALR(1) definition, say Bison uses LALR(1) by default rather
than implying Bison is limited to LALR(1).
(LocalWords): Add IELR.

diff --git a/NEWS b/NEWS
index f57b755..91bde87 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,35 @@ Bison News
 
 * Changes in version 2.5 (????-??-??):
 
+** IELR(1) and Canonical LR(1) Support
+
+  IELR(1) is a minimal LR(1) parser table generation algorithm.  That
+  is, given any context-free grammar, IELR(1) generates parser tables
+  with the full language recognition power of canonical LR(1) but with
+  nearly the same number of parser states as LALR(1).  This reduction in
+  parser states is often an order of magnitude.  More importantly,
+  because canonical LR(1)'s extra parser states may contain duplicate
+  conflicts in the case of non-LR(1) grammars, the number of conflicts
+  for IELR(1) is often an order of magnitude less as well.  This can
+  significantly reduce the complexity of developing of a grammar.
+
+  Bison can now generate IELR(1) and canonical LR(1) parser tables in
+  place of its traditional LALR(1) parser tables, which remain the
+  default.  You can specify the type of parser tables in the grammar
+  file with these directives:
+
+    %define lr.type "LALR"
+    %define lr.type "IELR"
+    %define lr.type "canonical LR"
+
+  The default rules optimization in the parser tables can also be
+  adjusted using `%define lr.default_rules'.  See the documentation for
+  `%define lr.type' and `%define lr.default_rules' in the section `Bison
+  Declaration Summary' in the Bison manual for the details.
+
+  These features are experimental.  More user feedback will help to
+  stabilize them.
+
 ** %define can now be invoked via the command line.
 
   Each of these bison command-line options
diff --git a/doc/bison.texinfo b/doc/bison.texinfo
index c8fa086..ed092e2 100644
--- a/doc/bison.texinfo
+++ b/doc/bison.texinfo
@@ -351,10 +351,12 @@ Copying This Manual
 @cindex introduction
 
 @dfn{Bison} is a general-purpose parser generator that converts an
-annotated context-free grammar into an @acronym{LALR}(1) or
address@hidden parser for that grammar.  Once you are proficient with
-Bison, you can use it to develop a wide range of language parsers, from those
-used in simple desk calculators to complex programming languages.
+annotated context-free grammar into a deterministic or @acronym{GLR}
+parser employing @acronym{LALR}(1), @acronym{IELR}(1), or canonical
address@hidden(1) parser tables.
+Once you are proficient with Bison, you can use it to develop a wide
+range of language parsers, from those used in simple desk calculators to
+complex programming languages.
 
 Bison is upward compatible with Yacc: all properly-written Yacc grammars
 ought to work with Bison with no change.  Anyone familiar with Yacc
@@ -460,26 +462,27 @@ order to specify the language Algol 60.  Any grammar 
expressed in
 essentially machine-readable @acronym{BNF}.
 
 @cindex @acronym{LALR}(1) grammars
address@hidden @acronym{IELR}(1) grammars
 @cindex @acronym{LR}(1) grammars
-There are various important subclasses of context-free grammar.  Although it
-can handle almost all context-free grammars, Bison is optimized for what
-are called @acronym{LALR}(1) grammars.
-In brief, in these grammars, it must be possible to
-tell how to parse any portion of an input string with just a single
-token of lookahead.  Strictly speaking, that is a description of an
address@hidden(1) grammar, and @acronym{LALR}(1) involves additional
-restrictions that are
-hard to explain simply; but it is rare in actual practice to find an
address@hidden(1) grammar that fails to be @acronym{LALR}(1).
+There are various important subclasses of context-free grammars.
+Although it can handle almost all context-free grammars, Bison is
+optimized for what are called @acronym{LR}(1) grammars.
+In brief, in these grammars, it must be possible to tell how to parse
+any portion of an input string with just a single token of lookahead.
+For historical reasons, Bison by default is limited by the additional
+restrictions of @acronym{LALR}(1), which is hard to explain simply.
 @xref{Mystery Conflicts, ,Mysterious Reduce/Reduce Conflicts}, for
 more information on this.
+To escape these additional restrictions, you can request
address@hidden(1) or canonical @acronym{LR}(1) parser tables.
address@hidden Summary,,lr.type}, to learn how.
 
 @cindex @acronym{GLR} parsing
 @cindex generalized @acronym{LR} (@acronym{GLR}) parsing
 @cindex ambiguous grammars
 @cindex nondeterministic parsing
 
-Parsers for @acronym{LALR}(1) grammars are @dfn{deterministic}, meaning
+Parsers for @acronym{LR}(1) grammars are @dfn{deterministic}, meaning
 roughly that the next grammar rule to apply at any point in the input is
 uniquely determined by the preceding input and a fixed, finite portion
 (called a @dfn{lookahead}) of the remaining input.  A context-free
@@ -708,8 +711,8 @@ from the values of the two subexpressions.
 @cindex shift/reduce conflicts
 @cindex reduce/reduce conflicts
 
-In some grammars, Bison's standard
address@hidden(1) parsing algorithm cannot decide whether to apply a
+In some grammars, Bison's deterministic
address@hidden(1) parsing algorithm cannot decide whether to apply a
 certain grammar rule at a given point.  That is, it may not be able to
 decide (on the basis of the input read so far) which of two possible
 reductions (applications of a grammar rule) applies, or whether to apply
@@ -718,13 +721,13 @@ input.  These are known respectively as 
@dfn{reduce/reduce} conflicts
 (@pxref{Reduce/Reduce}), and @dfn{shift/reduce} conflicts
 (@pxref{Shift/Reduce}).
 
-To use a grammar that is not easily modified to be @acronym{LALR}(1), a
+To use a grammar that is not easily modified to be @acronym{LR}(1), a
 more general parsing algorithm is sometimes necessary.  If you include
 @code{%glr-parser} among the Bison declarations in your file
 (@pxref{Grammar Outline}), the result is a Generalized @acronym{LR}
 (@acronym{GLR}) parser.  These parsers handle Bison grammars that
 contain no unresolved conflicts (i.e., after applying precedence
-declarations) identically to @acronym{LALR}(1) parsers.  However, when
+declarations) identically to deterministic parsers.  However, when
 faced with unresolved shift/reduce and reduce/reduce conflicts,
 @acronym{GLR} parsers use the simple expedient of doing both,
 effectively cloning the parser to follow both possibilities.  Each of
@@ -766,11 +769,8 @@ merged result.
 @cindex shift/reduce conflicts
 
 In the simplest cases, you can use the @acronym{GLR} algorithm
-to parse grammars that are unambiguous, but fail to be @acronym{LALR}(1).
-Such grammars typically require more than one symbol of lookahead,
-or (in rare cases) fall into the category of grammars in which the
address@hidden(1) algorithm throws away too much information (they are in
address@hidden(1), but not @acronym{LALR}(1), @ref{Mystery Conflicts}).
+to parse grammars that are unambiguous but fail to be @acronym{LR}(1).
+Such grammars typically require more than one symbol of lookahead.
 
 Consider a problem that
 arises in the declaration of enumerated and subrange types in the
@@ -807,7 +807,7 @@ type enum = (a);
 valid, and more-complicated cases can come up in practical programs.)
 
 These two declarations look identical until the @samp{..} token.
-With normal @acronym{LALR}(1) one-token lookahead it is not
+With normal @acronym{LR}(1) one-token lookahead it is not
 possible to decide between the two forms when the identifier
 @samp{a} is parsed.  It is, however, desirable
 for a parser to decide this, since in the latter case
@@ -846,9 +846,9 @@ reports a syntax error as usual.
 
 The effect of all this is that the parser seems to ``guess'' the
 correct branch to take, or in other words, it seems to use more
-lookahead than the underlying @acronym{LALR}(1) algorithm actually allows
-for.  In this example, @acronym{LALR}(2) would suffice, but also some cases
-that are not @acronym{LALR}(@math{k}) for any @math{k} can be handled this way.
+lookahead than the underlying @acronym{LR}(1) algorithm actually allows
+for.  In this example, @acronym{LR}(2) would suffice, but also some cases
+that are not @acronym{LR}(@math{k}) for any @math{k} can be handled this way.
 
 In general, a @acronym{GLR} parser can take quadratic or cubic worst-case time,
 and the current Bison parser even takes exponential time and space
@@ -901,7 +901,7 @@ expr : '(' expr ')'
 @end group
 @end example
 
-When used as a normal @acronym{LALR}(1) grammar, Bison correctly complains
+When used as a normal @acronym{LR}(1) grammar, Bison correctly complains
 about one reduce/reduce conflict.  In the conflicting situation the
 parser chooses one of the alternatives, arbitrarily the one
 declared first.  Therefore the following correct input is not
@@ -933,7 +933,7 @@ there are at least two potential problems to beware.  
First, always
 analyze the conflicts reported by Bison to make sure that @acronym{GLR}
 splitting is only done where it is intended.  A @acronym{GLR} parser
 splitting inadvertently may cause problems less obvious than an
address@hidden parser statically choosing the wrong alternative in a
address@hidden parser statically choosing the wrong alternative in a
 conflict.  Second, consider interactions with the lexer (@pxref{Semantic
 Tokens}) with great care.  Since a split parser consumes tokens without
 performing any actions during the split, the lexer cannot obtain
@@ -1153,7 +1153,7 @@ Another Bison feature requiring special consideration is 
@code{YYERROR}
 (@pxref{Action Features}), which you can invoke in a semantic action to
 initiate error recovery.
 During deterministic @acronym{GLR} operation, the effect of @code{YYERROR} is
-the same as its effect in an @acronym{LALR}(1) parser.
+the same as its effect in a deterministic parser.
 In a deferred semantic action, its effect is undefined.
 @c The effect is probably a syntax error at the split point.
 
@@ -4463,7 +4463,7 @@ be @var{n} shift/reduce conflicts and no reduce/reduce 
conflicts.
 Bison reports an error if the number of shift/reduce conflicts differs
 from @var{n}, or if there are any reduce/reduce conflicts.
 
-For normal @acronym{LALR}(1) parsers, reduce/reduce conflicts are more
+For deterministic parsers, reduce/reduce conflicts are more
 serious, and should be eliminated entirely.  Bison will always report
 reduce/reduce conflicts for these parsers.  With @acronym{GLR}
 parsers, however, both kinds of conflicts are routine; otherwise,
@@ -4887,7 +4887,7 @@ Some of the accepted @var{variable}s are:
 @findex %define api.push_pull
 
 @itemize @bullet
address@hidden Language(s): C (LALR(1) only)
address@hidden Language(s): C (deterministic parsers only)
 
 @item Purpose: Requests a pull parser, a push parser, or both.
 @xref{Push Decl, ,A Push Parser}.
@@ -4899,6 +4899,71 @@ More user feedback will help to stabilize it.)
 @item Default Value: @code{"pull"}
 @end itemize
 
address@hidden lr.default_rules
address@hidden default rules
address@hidden %define lr.default_rules
address@hidden delayed syntax errors
address@hidden syntax errors delayed
+
address@hidden @bullet
address@hidden Language(s): all
+
address@hidden Purpose: Specifies the kind of states that are permitted to
+contain default rules.
+That is, in such a state, Bison declares the rule with the largest
+lookahead set to be the default rule by which to reduce and then removes
+that lookahead set.
+The advantages of default rules are discussed below.
+The disadvantage is that, when the generated parser encounters a
+syntactically unacceptable token, the parser might then perform
+unnecessary reductions by default rules before it can detect the syntax
+error.
+
+(This feature is experimental.
+More user feedback will help to stabilize it.)
+
address@hidden Accepted Values:
address@hidden
address@hidden @code{"all"}.
+For @acronym{LALR} and @acronym{IELR} parsers (@pxref{Decl
+Summary,,lr.type}) by default, all states are permitted to contain
+default rules.
+The advantage is that parser table sizes can be significantly reduced.
+The reason Bison does not by default attempt to address the disadvantage
+of delayed syntax error detection is that this disadvantage is already
+inherent in @acronym{LALR} and @acronym{IELR} parser tables.
+That is, unlike a canonical @acronym{LR} state, an @acronym{LALR} or
address@hidden state can contain syntactically incorrect tokens in the
+lookahead sets of its rules.
+
address@hidden @code{"consistent"}.
address@hidden consistent states
+A consistent state is a state that has only one possible action.
+If that action is a reduction, then the parser does not need to request
+a lookahead token from the scanner before performing that action.
+However, the parser only recognizes the ability to ignore the lookahead
+token when such a reduction is encoded as a default rule.
+Thus, if default rules are permitted in and only in consistent states,
+then a canonical @acronym{LR} parser reports a syntax error as soon as
+it @emph{needs} the syntactically unacceptable token from the scanner.
+
address@hidden @code{"accepting"}.
address@hidden accepting state
+By default, the only default rule permitted in a canonical @acronym{LR}
+parser is the accept rule in the accepting state, which the parser
+reaches only after reading all tokens from the input.
+Thus, the default canonical @acronym{LR} parser reports a syntax error
+as soon as it @emph{reaches} the syntactically unacceptable token
+without performing any extra reductions.
address@hidden itemize
+
address@hidden Default Value:
address@hidden
address@hidden @code{"accepting"} if @code{lr.type} is @code{"canonical LR"}.
address@hidden @code{"all"} otherwise.
address@hidden itemize
address@hidden itemize
+
 @item lr.keep_unreachable_states
 @findex %define lr.keep_unreachable_states
 
@@ -4942,6 +5007,83 @@ However, Bison does not compute which goto actions are 
useless.
 @end itemize
 @end itemize
 
address@hidden lr.type
address@hidden %define lr.type
address@hidden @acronym{LALR}
address@hidden @acronym{IELR}
address@hidden @acronym{LR}
+
address@hidden @bullet
address@hidden Language(s): all
+
address@hidden Purpose: Specifies the type of parser tables within the
address@hidden(1) family.
+(This feature is experimental.
+More user feedback will help to stabilize it.)
+
address@hidden Accepted Values:
address@hidden
address@hidden @code{"LALR"}.
+While Bison generates @acronym{LALR} parser tables by default for
+historical reasons, @acronym{IELR} or canonical @acronym{LR} is almost
+always preferable for deterministic parsers.
+The trouble is that @acronym{LALR} parser tables can suffer from
+mysterious conflicts and may not accept the full set of sentences that
address@hidden and canonical @acronym{LR} accept.
address@hidden Conflicts}, for details.
+However, there are at least two scenarios where @acronym{LALR} may be
+worthwhile:
address@hidden
address@hidden @acronym{GLR} with @acronym{LALR}
address@hidden When employing @acronym{GLR} parsers (@pxref{GLR Parsers}), if 
you
+do not resolve any conflicts statically (for example, with @code{%left}
+or @code{%prec}), then the parser explores all potential parses of any
+given input.
+Thus, the use of @acronym{LALR} parser tables is guaranteed not to alter
+the language accepted by the parser.
address@hidden parser tables are the smallest parser tables Bison can
+currently generate, so they may be preferable.
+
address@hidden Occasionally during development, an especially malformed grammar
+with a major recurring flaw may severely impede the @acronym{IELR} or
+canonical @acronym{LR} parser table generation algorithm.
address@hidden can be a quick way to generate parser tables in order to
+investigate such problems while ignoring the more subtle differences
+from @acronym{IELR} and canonical @acronym{LR}.
address@hidden itemize
+
address@hidden @code{"IELR"}.
address@hidden is a minimal @acronym{LR} algorithm.
+That is, given any grammar (@acronym{LR} or address@hidden),
address@hidden and canonical @acronym{LR} always accept exactly the same
+set of sentences.
+However, as for @acronym{LALR}, the number of parser states is often an
+order of magnitude less for @acronym{IELR} than for canonical
address@hidden
+More importantly, because canonical @acronym{LR}'s extra parser states
+may contain duplicate conflicts in the case of address@hidden
+grammars, the number of conflicts for @acronym{IELR} is often an order
+of magnitude less as well.
+This can significantly reduce the complexity of developing of a grammar.
+
address@hidden @code{"canonical LR"}.
address@hidden delayed syntax errors
address@hidden syntax errors delayed
+The only advantage of canonical @acronym{LR} over @acronym{IELR} is that
+every canonical @acronym{LR} state encodes that state's exact set of
+syntactically acceptable tokens.
+The only difference in parsing behavior is then that the canonical
address@hidden parser can report a syntax error as soon as possible
+without performing any unnecessary reductions.
address@hidden Summary,,lr.default_rules}, for further details.
+Even when canonical @acronym{LR} behavior is ultimately desired,
address@hidden's elimination of duplicate conflicts should still
+facilitate the development of a grammar.
address@hidden itemize
+
address@hidden Default Value: @code{"LALR"}
address@hidden itemize
+
 @item namespace
 @findex %define namespace
 
@@ -6610,12 +6752,13 @@ a @code{name} if a comma or colon follows, or a 
@code{type} if another
 
 @cindex @acronym{LR}(1)
 @cindex @acronym{LALR}(1)
-However, Bison, like most parser generators, cannot actually handle all
address@hidden(1) grammars.  In this grammar, two contexts, that after
-an @code{ID}
-at the beginning of a @code{param_spec} and likewise at the beginning of
-a @code{return_spec}, are similar enough that Bison assumes they are the
-same.  They appear similar because the same set of rules would be
+However, for historical reasons, Bison cannot by default handle all
address@hidden(1) grammars.
+In this grammar, two contexts, that after an @code{ID} at the beginning
+of a @code{param_spec} and likewise at the beginning of a
address@hidden, are similar enough that Bison assumes they are the
+same.
+They appear similar because the same set of rules would be
 active---the rule for reducing to a @code{name} and that for reducing to
 a @code{type}.  Bison is unable to determine at that stage of processing
 that the rules would require different lookahead tokens in the two
@@ -6623,16 +6766,22 @@ contexts, so it makes a single parser state for them 
both.  Combining
 the two contexts causes a conflict later.  In parser terminology, this
 occurrence means that the grammar is not @acronym{LALR}(1).
 
-In general, it is better to fix deficiencies than to document them.  But
-this particular deficiency is intrinsically hard to fix; parser
-generators that can handle @acronym{LR}(1) grammars are hard to write
-and tend to
-produce parsers that are very large.  In practice, Bison is more useful
-as it is now.
-
-When the problem arises, you can often fix it by identifying the two
-parser states that are being confused, and adding something to make them
-look distinct.  In the above example, adding one rule to
+For many practical grammars (specifically those that fall into the
address@hidden(1) class), the limitations of @acronym{LALR}(1) result in
+difficulties beyond just mysterious reduce/reduce conflicts.
+The best way to fix all these problems is to select a different parser
+table generation algorithm.
+Either @acronym{IELR}(1) or canonical @acronym{LR}(1) would suffice, but
+the former is more efficient and easier to debug during development.
address@hidden Summary,,lr.type}, for details.
+(Bison's @acronym{IELR}(1) and canonical @acronym{LR}(1) implementations
+are experimental.
+More user feedback will help to stabilize them.)
+
+If you instead wish to work around @acronym{LALR}(1)'s limitations, you
+can often fix a mysterious conflict by identifying the two parser states
+that are being confused, and adding something to make them look
+distinct.  In the above example, adding one rule to
 @code{return_spec} as follows makes the problem go away:
 
 @example
@@ -6700,7 +6849,7 @@ The same is true of languages that require more than one 
symbol of
 lookahead, since the parser lacks the information necessary to make a
 decision at the point it must be made in a shift-reduce parser.
 Finally, as previously mentioned (@pxref{Mystery Conflicts}),
-there are languages where Bison's particular choice of how to
+there are languages where Bison's default choice of how to
 summarize the input seen so far loses necessary information.
 
 When you use the @samp{%glr-parser} declaration in your grammar file,
@@ -6732,7 +6881,7 @@ grammar symbol that produces the same segment of the 
input token
 stream.
 
 Whenever the parser makes a transition from having multiple
-states to having one, it reverts to the normal @acronym{LALR}(1) parsing
+states to having one, it reverts to the normal deterministic parsing
 algorithm, after resolving and executing the saved-up actions.
 At this transition, some of the states on the stack will have semantic
 values that are sets (actually multisets) of possible actions.  The
@@ -6745,9 +6894,9 @@ Bison resolves and evaluates both and then calls the 
merge function on
 the result.  Otherwise, it reports an ambiguity.
 
 It is possible to use a data structure for the @acronym{GLR} parsing tree that
-permits the processing of any @acronym{LALR}(1) grammar in linear time (in the
+permits the processing of any @acronym{LR}(1) grammar in linear time (in the
 size of the input), any unambiguous (not necessarily
address@hidden(1)) grammar in
address@hidden(1)) grammar in
 quadratic worst-case time, and any general (possibly ambiguous)
 context-free grammar in cubic worst-case time.  However, Bison currently
 uses a simpler data structure that requires time proportional to the
@@ -6757,9 +6906,9 @@ grammars can require exponential time and space to 
process.  Such badly
 behaving examples, however, are not generally of practical interest.
 Usually, nondeterminism in a grammar is local---the parser is ``in
 doubt'' only for a few tokens at a time.  Therefore, the current data
-structure should generally be adequate.  On @acronym{LALR}(1) portions of a
-grammar, in particular, it is only slightly slower than with the default
-Bison parser.
+structure should generally be adequate.  On @acronym{LR}(1) portions of a
+grammar, in particular, it is only slightly slower than with the
+deterministic @acronym{LR}(1) Bison parser.
 
 For a more detailed exposition of @acronym{GLR} parsers, please see: Elizabeth
 Scott, Adrian Johnstone and Shamsa Sadaf Hussain, Tomita-Style
@@ -6808,16 +6957,16 @@ The default value of @code{YYMAXDEPTH}, if you do not 
define it, is
 
 @vindex YYINITDEPTH
 You can control how much stack is allocated initially by defining the
-macro @code{YYINITDEPTH} to a positive integer.  For the C
address@hidden(1) parser, this value must be a compile-time constant
+macro @code{YYINITDEPTH} to a positive integer.  For the deterministic
+parser in C, this value must be a compile-time constant
 unless you are assuming C99 or some other target language or compiler
 that allows variable-length arrays.  The default is 200.
 
 Do not allow @code{YYINITDEPTH} to be greater than @code{YYMAXDEPTH}.
 
 @c FIXME: C++ output.
-Because of semantical differences between C and C++, the
address@hidden(1) parsers in C produced by Bison cannot grow when compiled
+Because of semantical differences between C and C++, the deterministic
+parsers in C produced by Bison cannot grow when compiled
 by C++ compilers.  In this precise case (compiling a C parser as C++) you are
 suggested to grow @code{YYINITDEPTH}.  The Bison maintainers hope to fix
 this deficiency in a future release.
@@ -7205,7 +7354,8 @@ useless: STR;
 @command{bison} reports:
 
 @example
-calc.y: warning: 1 nonterminal and 1 rule useless in grammar
+tmp.y: warning: 1 nonterminal useless in grammar
+tmp.y: warning: 1 rule useless in grammar
 calc.y:11.1-7: warning: nonterminal useless in grammar: useless
 calc.y:11.10-12: warning: rule useless in grammar: useless: STR
 calc.y: conflicts: 7 shift/reduce
@@ -7393,6 +7543,7 @@ control will jump to state 4, corresponding to the item 
@samp{exp -> exp
 '+' . exp}.  Since there is no default action, any other token than
 those listed above will trigger a syntax error.
 
address@hidden accepting state
 The state 3 is named the @dfn{final state}, or the @dfn{accepting
 state}:
 
@@ -7473,7 +7624,7 @@ 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, Bison
+Because in deterministic parsing a single decision can be made, Bison
 arbitrarily chose to disable the reduction, see @ref{Shift/Reduce, ,
 Shift/Reduce Conflicts}.  Discarded actions are reported in between
 square brackets.
@@ -7767,7 +7918,7 @@ other minor ways.  Most importantly, imitate Yacc's output
 file name conventions, so that the parser output file is called
 @file{y.tab.c}, and the other outputs are called @file{y.output} and
 @file{y.tab.h}.
-Also, if generating an @acronym{LALR}(1) parser in C, generate @code{#define}
+Also, if generating a deterministic parser in C, generate @code{#define}
 statements in addition to an @code{enum} to associate token numbers with token
 names.
 Thus, the following shell script can substitute for Yacc, and the Bison
@@ -7914,7 +8065,7 @@ separated list of @var{things} among:
 @table @code
 @item state
 Description of the grammar, conflicts (resolved and unresolved), and
address@hidden automaton.
+parser's automaton.
 
 @item lookahead
 Implies @code{state} and augments the description of the automaton with
@@ -7943,7 +8094,7 @@ described under the @samp{-v} and @samp{-d} options.
 
 @item -g address@hidden
 @itemx address@hidden
-Output a graphical representation of the @acronym{LALR}(1) grammar
+Output a graphical representation of the parser's
 automaton computed by Bison, in @uref{http://www.graphviz.org/, Graphviz}
 @uref{http://www.graphviz.org/doc/info/lang.html, @acronym{DOT}} format.
 @address@hidden is optional.
@@ -7952,7 +8103,7 @@ If omitted and the grammar file is @file{foo.y}, the 
output file will be
 
 @item -x address@hidden
 @itemx address@hidden
-Output an XML report of the @acronym{LALR}(1) automaton computed by Bison.
+Output an XML report of the parser's automaton computed by Bison.
 @address@hidden is optional.
 If omitted and the grammar file is @file{foo.y}, the output file will be
 @file{foo.xml}.
@@ -8025,7 +8176,7 @@ int yyparse (void);
 @c - Always pure
 @c - initial action
 
-The C++ @acronym{LALR}(1) parser is selected using the skeleton directive,
+The C++ deterministic parser is selected using the skeleton directive,
 @samp{%skeleton "lalr1.c"}, or the synonymous command-line option
 @option{--skeleton=lalr1.c}.
 @xref{Decl Summary}.
@@ -8414,10 +8565,10 @@ calcxx_driver::error (const std::string& m)
 @subsubsection Calc++ Parser
 
 The parser definition file @file{calc++-parser.yy} starts by asking for
-the C++ LALR(1) skeleton, the creation of the parser header file, and
-specifies the name of the parser class.  Because the C++ skeleton
-changed several times, it is safer to require the version you designed
-the grammar for.
+the C++ deterministic parser skeleton, the creation of the parser header
+file, and specifies the name of the parser class.
+Because the C++ skeleton changed several times, it is safer to require
+the version you designed the grammar for.
 
 @comment file: calc++-parser.yy
 @example
@@ -10151,8 +10302,8 @@ is recovering from a syntax error, and 0 otherwise.
 @end deffn
 
 @deffn {Macro} YYSTACK_USE_ALLOCA
-Macro used to control the use of @code{alloca} when the C
address@hidden(1) parser needs to extend its stacks.  If defined to 0,
+Macro used to control the use of @code{alloca} when the
+deterministic parser in C needs to extend its stacks.  If defined to 0,
 the parser will use @code{malloc} to extend its stacks.  If defined to
 1, the parser will use @code{alloca}.  Values other than 0 and 1 are
 reserved for future Bison extensions.  If not defined,
@@ -10177,12 +10328,21 @@ Data type of semantic values; @code{int} by default.
 @cindex glossary
 
 @table @asis
address@hidden Accepting State
+A state whose only action is the accept action.
+The accepting state is thus a consistent state.
address@hidden,,}.
+
 @item Backus-Naur Form (@acronym{BNF}; also called ``Backus Normal Form'')
 Formal method of specifying context-free grammars originally proposed
 by John Backus, and slightly improved by Peter Naur in his 1960-01-02
 committee document contributing to what became the Algol 60 report.
 @xref{Language and Grammar, ,Languages and Context-Free Grammars}.
 
address@hidden Consistent State
+A state containing only one possible action.
address@hidden Summary,,lr.default_rules}.
+
 @item Context-free grammars
 Grammars specified as rules that can be applied regardless of context.
 Thus, if there is a rule which says that an integer can be used as an
@@ -10190,6 +10350,13 @@ expression, integers are allowed @emph{anywhere} an 
expression is
 permitted.  @xref{Language and Grammar, ,Languages and Context-Free
 Grammars}.
 
address@hidden Default Rule
+The rule by which a parser should reduce if the current parser state
+contains no other action for the lookahead token.
+In permitted parser states, Bison declares the rule with the largest
+lookahead set to be the default rule and removes that lookahead set.
address@hidden Summary,,lr.default_rules}.
+
 @item Dynamic allocation
 Allocation of memory that occurs during execution, rather than at
 compile time or on entry to a function.
@@ -10208,8 +10375,8 @@ rules.  @xref{Algorithm, ,The Bison Parser Algorithm}.
 
 @item Generalized @acronym{LR} (@acronym{GLR})
 A parsing algorithm that can handle all context-free grammars, including those
-that are not @acronym{LALR}(1).  It resolves situations that Bison's
-usual @acronym{LALR}(1)
+that are not @acronym{LR}(1).  It resolves situations that Bison's
+deterministic parsing
 algorithm cannot by effectively splitting off multiple parsers, trying all
 possible parsers, and discarding those that fail in the light of additional
 right context.  @xref{Generalized LR Parsing, ,Generalized
@@ -10220,6 +10387,20 @@ A language construct that is (in general) 
grammatically divisible;
 for example, `expression' or `declaration' in address@hidden
 @xref{Language and Grammar, ,Languages and Context-Free Grammars}.
 
address@hidden @acronym{IELR}(1)
+A minimal @acronym{LR}(1) parser table generation algorithm.
+That is, given any context-free grammar, @acronym{IELR}(1) generates
+parser tables with the full language recognition power of canonical
address@hidden(1) but with nearly the same number of parser states as
address@hidden(1).
+This reduction in parser states is often an order of magnitude.
+More importantly, because canonical @acronym{LR}(1)'s extra parser
+states may contain duplicate conflicts in the case of
address@hidden(1) grammars, the number of conflicts for
address@hidden(1) is often an order of magnitude less as well.
+This can significantly reduce the complexity of developing of a grammar.
address@hidden Summary,,lr.type}.
+
 @item Infix operator
 An arithmetic operator that is placed between the operands on which it
 performs some operation.
@@ -10263,8 +10444,8 @@ Tokens}.
 
 @item @acronym{LALR}(1)
 The class of context-free grammars that Bison (like most other parser
-generators) can handle; a subset of @acronym{LR}(1).  @xref{Mystery
-Conflicts, ,Mysterious Reduce/Reduce Conflicts}.
+generators) can handle by default; a subset of @acronym{LR}(1).
address@hidden Conflicts, ,Mysterious Reduce/Reduce Conflicts}.
 
 @item @acronym{LR}(1)
 The class of context-free grammars in which at most one token of
@@ -10382,4 +10563,4 @@ grammatically indivisible.  The piece of text it 
represents is a token.
 @c LocalWords: infile ypp yxx outfile itemx tex leaderfill
 @c LocalWords: hbox hss hfill tt ly yyin fopen fclose ofirst gcc ll
 @c LocalWords: nbar yytext fst snd osplit ntwo strdup AST
address@hidden LocalWords: YYSTACK DVI fdl printindex
address@hidden LocalWords: YYSTACK DVI fdl printindex IELR
diff --git a/src/getargs.c b/src/getargs.c
index 4b35171..2f2e900 100644
--- a/src/getargs.c
+++ b/src/getargs.c
@@ -257,7 +257,8 @@ usage (int status)
 
       printf (_("Usage: %s [OPTION]... FILE\n"), program_name);
       fputs (_("\
-Generate LALR(1) and GLR parsers.\n\
+Generate a deterministic or GLR parser employing LALR(1), IELR(1), or\n\
+canonical LR(1) parser tables.\n\
 \n\
 "), stdout);
 
-- 
1.5.4.3