+2006-06-09 Joel E. Denny <jdenny@ces.clemson.edu>
+
+ For consistency, use `lookahead' instead of `look-ahead' or
+ `look_ahead'. Discussed starting at
+ <http://lists.gnu.org/archive/html/bison-patches/2006-01/msg00049.html>
+ and then at
+ <http://lists.gnu.org/archive/html/bison-patches/2006-06/msg00017.html>.
+ * NEWS: For the next release, note the change to `--report'.
+ * TODO, doc/bison.1: Update English.
+ * doc/bison.texinfo: Update English.
+ (Understanding Your Parser, Bison Options): Document as
+ `--report=lookahead' rather than `--report=look-ahead'.
+ * src/conflicts.c: Update English in comments.
+ (lookahead_set): Rename from look_ahead_set.
+ (flush_reduce): Rename argument look_ahead_tokens to lookahead_tokens.
+ (resolve_sr_conflict): Rename local look_ahead_tokens to
+ lookahead_tokens, and update other uses.
+ (flush_shift, set_conflicts, conflicts_solve, count_sr_conflicts,
+ count_rr_conflicts, conflicts_free): Update uses.
+ * src/getargs.c (report_args): Move "lookahead" before alternate
+ spellings.
+ (report_types): Update uses.
+ (usage): For `--report' usage description, state `lookahead' spelling
+ rather than `look-ahead'.
+ * src/getargs.h (report.report_lookahead_tokens): Rename from
+ report_look_ahead_tokens.
+ * src/lalr.c: Update English in comments.
+ (compute_lookahead_tokens): Rename from compute_look_ahead_tokens.
+ (state_lookahead_tokens_count): Rename from
+ state_look_ahead_tokens_count.
+ Rename local n_look_ahead_tokens to n_lookahead_tokens.
+ (lookahead_tokens_print): Rename from look_ahead_tokens_print.
+ Rename local n_look_ahead_tokens to n_lookahead_tokens.
+ Update other uses.
+ Update English in output.
+ (add_lookback_edge, initialize_LA, lalr, lalr_free): Update uses.
+ * src/print.c: Update English in comments.
+ (lookahead_set): Rename from look_ahead_set.
+ (print_reduction): Rename argument lookahead_token from
+ look_ahead_token.
+ (print_core, state_default_rule, print_reductions, print_results):
+ Update uses.
+ * src/print_graph.c: Update English in comments.
+ (print_core): Update uses.
+ * src/state.c: Update English in comments.
+ (reductions_new): Update uses.
+ (state_rule_lookahead_tokens_print): Rename from
+ state_rule_look_ahead_tokens_print, and update other uses.
+ * src/state.h: Update English in comments.
+ (reductions.lookahead_tokens): Rename from look_ahead_tokens.
+ (state_rule_lookahead_tokens_print): Rename from
+ state_rule_look_ahead_tokens_print.
+ * src/tables.c: Update English in comments.
+ (conflict_row, action_row): Update uses.
+ * tests/glr-regression.at
+ (Incorrect lookahead during deterministic GLR,
+ Incorrect lookahead during nondeterministic GLR): Rename
+ print_look_ahead to print_lookahead.
+ * tests/torture.at: Update English in comments.
+ (AT_DATA_LOOKAHEAD_TOKENS_GRAMMAR): Rename from
+ AT_DATA_LOOK_AHEAD_TOKENS_GRAMMAR.
+ (Many lookahead tokens): Update uses.
+ * data/glr.c: Update English in comments.
+ * lalr1.cc: Likewise.
+ * yacc.c: Likewise.
+ * src/conflicts.h: Likewise.
+ * src/lalr.h: Likewise.
+ * src/main.c: Likewise.
+ * src/output.c: Likewise.
+ * src/parse-gram.c: Likewise.
+ * src/tables.h: Likewise.
+ * tests/calc.at: Likewise.
+
2006-06-08 Joel E. Denny <jdenny@ces.clemson.edu>
* src/flex-scanner.h (yytext): Remove stray `*/' in #define.
Bison News
----------
+Changes in version 2.3+:
+
+* The option `--report=look-ahead' has been changed to `--report=lookahead'.
+ The old spelling still works but is not documented and will be removed.
+
Changes in version 2.3, 2006-06-05:
* GLR grammars should now use `YYRECOVERING ()' instead of `YYRECOVERING',
** GLR
How would Paul like to display the conflicted actions? In particular,
-what when two reductions are possible on a given look-ahead token, but one is
+what when two reductions are possible on a given lookahead token, but one is
part of $default. Should we make the two reductions explicit, or just
keep $default? See the following point.
# b4_lyyerror_args
# ----------------
-# Same as above, but on the look-ahead, hence &yylloc instead of yylocp.
+# Same as above, but on the lookahead, hence &yylloc instead of yylocp.
m4_define([b4_lyyerror_args],
[b4_pure_if([b4_locations_if([&yylloc, ])])dnl
m4_ifset([b4_parse_param], [b4_c_args(b4_parse_param), ])])
# b4_lpure_args
# -------------
-# Same as above, but on the look-ahead, hence &yylloc instead of yylocp.
+# Same as above, but on the lookahead, hence &yylloc instead of yylocp.
m4_define([b4_lpure_args],
[b4_pure_if([b4_locations_if([, &yylloc])])[]b4_user_args])
/* Recover from a syntax error on *YYSTACKP, assuming that *YYSTACKP->YYTOKENP,
yylval, and yylloc are the syntactic category, semantic value, and location
- of the look-ahead. */
+ of the lookahead. */
/*ARGSUSED*/ static void
yyrecoverSyntaxError (yyGLRStack* yystackp]b4_user_formals[)
{
/// Generate an error message.
/// \param state the state where the error occurred.
- /// \param tok the look-ahead token.
+ /// \param tok the lookahead token.
virtual std::string yysyntax_error_ (int yystate]dnl
b4_error_verbose_if([, int tok])[);
int
]b4_parser_class_name[::parse ()
{
- /// Look-ahead and look-ahead in internal form.
+ /// Lookahead and lookahead in internal form.
int yychar = yyempty_;
int yytoken = 0;
int yynerrs_ = 0;
int yyerrstatus_ = 0;
- /// Semantic value of the look-ahead.
+ /// Semantic value of the lookahead.
semantic_type yylval;
- /// Location of the look-ahead.
+ /// Location of the lookahead.
location_type yylloc;
/// The locations where the error started and ended.
location yyerror_range[2];
/* Backup. */
yybackup:
- /* Try to take a decision without look-ahead. */
+ /* Try to take a decision without lookahead. */
yyn = yypact_[yystate];
if (yyn == yypact_ninf_)
goto yydefault;
- /* Read a look-ahead token. */
+ /* Read a lookahead token. */
if (yychar == yyempty_)
{
YYCDEBUG << "Reading a token: ";
if (yyn == yyfinal_)
goto yyacceptlab;
- /* Shift the look-ahead token. */
+ /* Shift the lookahead token. */
YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
/* Discard the token being shifted unless it is eof. */
yyerror_range[0] = yylloc;
if (yyerrstatus_ == 3)
{
- /* If just tried and failed to reuse look-ahead token after an
+ /* If just tried and failed to reuse lookahead token after an
error, discard it. */
if (yychar <= yyeof_)
}
}
- /* Else will try to reuse look-ahead token after shifting the error
+ /* Else will try to reuse lookahead token after shifting the error
token. */
goto yyerrlab1;
yyerror_range[1] = yylloc;
// Using YYLLOC is tempting, but would change the location of
- // the look-ahead. YYLOC is available though.
+ // the lookahead. YYLOC is available though.
YYLLOC_DEFAULT (yyloc, (yyerror_range - 1), 2);
yysemantic_stack_.push (yylval);
yylocation_stack_.push (yyloc);
# Declare the variables that are global, or local to YYPARSE if
# pure-parser.
m4_define([b4_declare_parser_variables],
-[/* The look-ahead symbol. */
+[/* The lookahead symbol. */
int yychar;
-/* The semantic value of the look-ahead symbol. */
+/* The semantic value of the lookahead symbol. */
YYSTYPE yylval;
/* Number of syntax errors so far. */
int yynerrs;b4_locations_if([
-/* Location data for the look-ahead symbol. */
+/* Location data for the lookahead symbol. */
YYLTYPE yylloc;])
])
m4_divert_pop([KILL])dnl# ====================== End of M4 code.
int yyresult;
/* Number of tokens to shift before error messages enabled. */
int yyerrstatus;
- /* Look-ahead token as an internal (translated) token number. */
+ /* Lookahead token as an internal (translated) token number. */
int yytoken = 0;
#if YYERROR_VERBOSE
/* Buffer for error messages, and its allocated size. */
yybackup:
/* Do appropriate processing given the current state. Read a
- look-ahead token if we need one and don't already have one. */
+ lookahead token if we need one and don't already have one. */
- /* First try to decide what to do without reference to look-ahead token. */
+ /* First try to decide what to do without reference to lookahead token. */
yyn = yypact[yystate];
if (yyn == YYPACT_NINF)
goto yydefault;
- /* Not known => get a look-ahead token if don't already have one. */
+ /* Not known => get a lookahead token if don't already have one. */
- /* YYCHAR is either YYEMPTY or YYEOF or a valid look-ahead symbol. */
+ /* YYCHAR is either YYEMPTY or YYEOF or a valid lookahead symbol. */
if (yychar == YYEMPTY)
{
YYDPRINTF ((stderr, "Reading a token: "));
if (yyerrstatus)
yyerrstatus--;
- /* Shift the look-ahead token. */
+ /* Shift the lookahead token. */
YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
/* Discard the shifted token unless it is eof. */
if (yyerrstatus == 3)
{
- /* If just tried and failed to reuse look-ahead token after an
+ /* If just tried and failed to reuse lookahead token after an
error, discard it. */
if (yychar <= YYEOF)
}
}
- /* Else will try to reuse look-ahead token after shifting the error
+ /* Else will try to reuse lookahead token after shifting the error
token. */
goto yyerrlab1;
]b4_locations_if([[
yyerror_range[1] = yylloc;
/* Using YYLLOC is tempting, but would change the location of
- the look-ahead. YYLOC is available though. */
+ the lookahead. YYLOC is available though. */
YYLLOC_DEFAULT (yyloc, (yyerror_range - 1), 2);
*++yylsp = yyloc;]])[
.TP
.B \-\-verbose
Write an extra output file containing verbose descriptions of the
-parser states and what is done for each type of look-ahead token in
+parser states and what is done for each type of lookahead token in
that state.
.sp
This file also describes all the conflicts, both those resolved by
The Bison Parser Algorithm
-* Look-Ahead:: Parser looks one token ahead when deciding what to do.
+* Lookahead:: Parser looks one token ahead when deciding what to do.
* Shift/Reduce:: Conflicts: when either shifting or reduction is valid.
* Precedence:: Operator precedence works by resolving conflicts.
* Contextual Precedence:: When an operator's precedence depends on context.
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 look-ahead. Strictly speaking, that is a description of an
+token of lookahead. Strictly speaking, that is a description of an
@acronym{LR}(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
Parsers for @acronym{LALR}(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{look-ahead}) of the remaining input. A context-free
+(called a @dfn{lookahead}) of the remaining input. A context-free
grammar can be @dfn{ambiguous}, meaning that there are multiple ways to
apply the grammar rules to get the same inputs. Even unambiguous
grammars can be @dfn{nondeterministic}, meaning that no fixed
-look-ahead always suffices to determine the next grammar rule to apply.
+lookahead always suffices to determine the next grammar rule to apply.
With the proper declarations, Bison is also able to parse these more
general context-free grammars, using a technique known as @acronym{GLR}
parsing (for Generalized @acronym{LR}). Bison's @acronym{GLR} parsers
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 look-ahead,
+Such grammars typically require more than one symbol of lookahead,
or (in rare cases) fall into the category of grammars in which the
@acronym{LALR}(1) algorithm throws away too much information (they are in
@acronym{LR}(1), but not @acronym{LALR}(1), @ref{Mystery Conflicts}).
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 look-ahead it is not
+With normal @acronym{LALR}(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
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
-look-ahead than the underlying @acronym{LALR}(1) algorithm actually allows
+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.
@vindex yylloc
@cindex @acronym{GLR} parsers and @code{yylloc}
In any semantic action, you can examine @code{yychar} to determine the type of
-the look-ahead token present at the time of the associated reduction.
+the lookahead token present at the time of the associated reduction.
After checking that @code{yychar} is not set to @code{YYEMPTY} or @code{YYEOF},
you can then examine @code{yylval} and @code{yylloc} to determine the
-look-ahead token's semantic value and location, if any.
+lookahead token's semantic value and location, if any.
In a nondeferred semantic action, you can also modify any of these variables to
influence syntax analysis.
-@xref{Look-Ahead, ,Look-Ahead Tokens}.
+@xref{Lookahead, ,Lookahead Tokens}.
@findex yyclearin
@cindex @acronym{GLR} parsers and @code{yyclearin}
definition of @code{foo}.
@vindex yylval
-It is also possible to access the semantic value of the look-ahead token, if
+It is also possible to access the semantic value of the lookahead token, if
any, from a semantic action.
This semantic value is stored in @code{yylval}.
@xref{Action Features, ,Special Features for Use in Actions}.
when it has read no farther than the open-brace. In other words, it
must commit to using one rule or the other, without sufficient
information to do it correctly. (The open-brace token is what is called
-the @dfn{look-ahead} token at this time, since the parser is still
-deciding what to do about it. @xref{Look-Ahead, ,Look-Ahead Tokens}.)
+the @dfn{lookahead} token at this time, since the parser is still
+deciding what to do about it. @xref{Lookahead, ,Lookahead Tokens}.)
You might think that you could correct the problem by putting identical
actions into the two rules, like this:
@end example
@vindex yylloc
-It is also possible to access the location of the look-ahead token, if any,
+It is also possible to access the location of the lookahead token, if any,
from a semantic action.
This location is stored in @code{yylloc}.
@xref{Action Features, ,Special Features for Use in Actions}.
@findex %initial-action
Declare that the braced @var{code} must be invoked before parsing each time
@code{yyparse} is called. The @var{code} may use @code{$$} and
-@code{@@$} --- initial value and location of the look-ahead --- and the
+@code{@@$} --- initial value and location of the lookahead --- and the
@code{%parse-param}.
@end deffn
@item
incoming terminals during the second phase of error recovery,
@item
-the current look-ahead and the entire stack (except the current
+the current lookahead and the entire stack (except the current
right-hand side symbols) when the parser returns immediately, and
@item
the start symbol, when the parser succeeds.
@deffn {Directive} %verbose
Write an extra output file containing verbose descriptions of the
-parser states and what is done for each type of look-ahead token in
+parser states and what is done for each type of lookahead token in
that state. @xref{Understanding, , Understanding Your Parser}, for more
information.
@end deffn
@deffn {Macro} YYBACKUP (@var{token}, @var{value});
@findex YYBACKUP
Unshift a token. This macro is allowed only for rules that reduce
-a single value, and only when there is no look-ahead token.
+a single value, and only when there is no lookahead token.
It is also disallowed in @acronym{GLR} parsers.
-It installs a look-ahead token with token type @var{token} and
+It installs a lookahead token with token type @var{token} and
semantic value @var{value}; then it discards the value that was
going to be reduced by this rule.
If the macro is used when it is not valid, such as when there is
-a look-ahead token already, then it reports a syntax error with
+a lookahead token already, then it reports a syntax error with
a message @samp{cannot back up} and performs ordinary error
recovery.
@deffn {Macro} YYEMPTY
@vindex YYEMPTY
-Value stored in @code{yychar} when there is no look-ahead token.
+Value stored in @code{yychar} when there is no lookahead token.
@end deffn
@deffn {Macro} YYEOF
@vindex YYEOF
-Value stored in @code{yychar} when the look-ahead is the end of the input
+Value stored in @code{yychar} when the lookahead is the end of the input
stream.
@end deffn
@end deffn
@deffn {Variable} yychar
-Variable containing either the look-ahead token, or @code{YYEOF} when the
-look-ahead is the end of the input stream, or @code{YYEMPTY} when no look-ahead
+Variable containing either the lookahead token, or @code{YYEOF} when the
+lookahead is the end of the input stream, or @code{YYEMPTY} when no lookahead
has been performed so the next token is not yet known.
Do not modify @code{yychar} in a deferred semantic action (@pxref{GLR Semantic
Actions}).
-@xref{Look-Ahead, ,Look-Ahead Tokens}.
+@xref{Lookahead, ,Lookahead Tokens}.
@end deffn
@deffn {Macro} yyclearin;
-Discard the current look-ahead token. This is useful primarily in
+Discard the current lookahead token. This is useful primarily in
error rules.
Do not invoke @code{yyclearin} in a deferred semantic action (@pxref{GLR
Semantic Actions}).
@end deffn
@deffn {Variable} yylloc
-Variable containing the look-ahead token location when @code{yychar} is not set
+Variable containing the lookahead token location when @code{yychar} is not set
to @code{YYEMPTY} or @code{YYEOF}.
Do not modify @code{yylloc} in a deferred semantic action (@pxref{GLR Semantic
Actions}).
@end deffn
@deffn {Variable} yylval
-Variable containing the look-ahead token semantic value when @code{yychar} is
+Variable containing the lookahead token semantic value when @code{yychar} is
not set to @code{YYEMPTY} or @code{YYEOF}.
Do not modify @code{yylval} in a deferred semantic action (@pxref{GLR Semantic
Actions}).
This kind of parser is known in the literature as a bottom-up parser.
@menu
-* Look-Ahead:: Parser looks one token ahead when deciding what to do.
+* Lookahead:: Parser looks one token ahead when deciding what to do.
* Shift/Reduce:: Conflicts: when either shifting or reduction is valid.
* Precedence:: Operator precedence works by resolving conflicts.
* Contextual Precedence:: When an operator's precedence depends on context.
* Memory Management:: What happens when memory is exhausted. How to avoid it.
@end menu
-@node Look-Ahead
-@section Look-Ahead Tokens
-@cindex look-ahead token
+@node Lookahead
+@section Lookahead Tokens
+@cindex lookahead token
The Bison parser does @emph{not} always reduce immediately as soon as the
last @var{n} tokens and groupings match a rule. This is because such a
token in order to decide what to do.
When a token is read, it is not immediately shifted; first it becomes the
-@dfn{look-ahead token}, which is not on the stack. Now the parser can
+@dfn{lookahead token}, which is not on the stack. Now the parser can
perform one or more reductions of tokens and groupings on the stack, while
-the look-ahead token remains off to the side. When no more reductions
-should take place, the look-ahead token is shifted onto the stack. This
+the lookahead token remains off to the side. When no more reductions
+should take place, the lookahead token is shifted onto the stack. This
does not mean that all possible reductions have been done; depending on the
-token type of the look-ahead token, some rules may choose to delay their
+token type of the lookahead token, some rules may choose to delay their
application.
-Here is a simple case where look-ahead is needed. These three rules define
+Here is a simple case where lookahead is needed. These three rules define
expressions which contain binary addition operators and postfix unary
factorial operators (@samp{!}), and allow parentheses for grouping.
@vindex yychar
@vindex yylval
@vindex yylloc
-The look-ahead token is stored in the variable @code{yychar}.
+The lookahead token is stored in the variable @code{yychar}.
Its semantic value and location, if any, are stored in the variables
@code{yylval} and @code{yylloc}.
@xref{Action Features, ,Special Features for Use in Actions}.
Here we assume that @code{IF}, @code{THEN} and @code{ELSE} are
terminal symbols for specific keyword tokens.
-When the @code{ELSE} token is read and becomes the look-ahead token, the
+When the @code{ELSE} token is read and becomes the lookahead token, the
contents of the stack (assuming the input is valid) are just right for
reduction by the first rule. But it is also legitimate to shift the
@code{ELSE}, because that would lead to eventual reduction by the second
The latter alternative, @dfn{right association}, is desirable for
assignment operators. The choice of left or right association is a
matter of whether the parser chooses to shift or reduce when the stack
-contains @w{@samp{1 - 2}} and the look-ahead token is @samp{-}: shifting
+contains @w{@samp{1 - 2}} and the lookahead token is @samp{-}: shifting
makes right-associativity.
@node Using Precedence
Precedence, ,Context-Dependent Precedence}.)
Finally, the resolution of conflicts works by comparing the precedence
-of the rule being considered with that of the look-ahead token. If the
+of the rule being considered with that of the lookahead token. If the
token's precedence is higher, the choice is to shift. If the rule's
precedence is higher, the choice is to reduce. If they have equal
precedence, the choice is made based on the associativity of that
resolved.
Not all rules and not all tokens have precedence. If either the rule or
-the look-ahead token has no precedence, then the default is to shift.
+the lookahead token has no precedence, then the default is to shift.
@node Contextual Precedence
@section Context-Dependent Precedence
near the top of the stack. The current state collects all the information
about previous input which is relevant to deciding what to do next.
-Each time a look-ahead token is read, the current parser state together
-with the type of look-ahead token are looked up in a table. This table
-entry can say, ``Shift the look-ahead token.'' In this case, it also
+Each time a lookahead token is read, the current parser state together
+with the type of lookahead token are looked up in a table. This table
+entry can say, ``Shift the lookahead token.'' In this case, it also
specifies the new parser state, which is pushed onto the top of the
parser stack. Or it can say, ``Reduce using rule number @var{n}.''
This means that a certain number of tokens or groupings are taken off
that number of states are popped from the stack, and one new state is
pushed.
-There is one other alternative: the table can say that the look-ahead token
+There is one other alternative: the table can say that the lookahead token
is erroneous in the current state. This causes error processing to begin
(@pxref{Error Recovery}).
@end example
It would seem that this grammar can be parsed with only a single token
-of look-ahead: when a @code{param_spec} is being read, an @code{ID} is
+of lookahead: when a @code{param_spec} is being read, an @code{ID} is
a @code{name} if a comma or colon follows, or a @code{type} if another
@code{ID} follows. In other words, this grammar is @acronym{LR}(1).
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 look-ahead tokens in the two
+that the rules would require different lookahead tokens in the two
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).
Bison produces @emph{deterministic} parsers that choose uniquely
when to reduce and which reduction to apply
-based on a summary of the preceding input and on one extra token of look-ahead.
+based on a summary of the preceding input and on one extra token of lookahead.
As a result, normal Bison handles a proper subset of the family of
context-free languages.
Ambiguous grammars, since they have strings with more than one possible
sequence of reductions cannot have deterministic parsers in this sense.
The same is true of languages that require more than one symbol of
-look-ahead, since the parser lacks the information necessary to make a
+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
@code{error} token is acceptable. (This means that the subexpressions
already parsed are discarded, back to the last complete @code{stmnts}.)
At this point the @code{error} token can be shifted. Then, if the old
-look-ahead token is not acceptable to be shifted next, the parser reads
+lookahead token is not acceptable to be shifted next, the parser reads
tokens and discards them until it finds a token which is acceptable. In
this example, Bison reads and discards input until the next newline so
that the fourth rule can apply. Note that discarded symbols are
@samp{yyerrok;} is a valid C statement.
@findex yyclearin
-The previous look-ahead token is reanalyzed immediately after an error. If
+The previous lookahead token is reanalyzed immediately after an error. If
this is unacceptable, then the macro @code{yyclearin} may be used to clear
this token. Write the statement @samp{yyclearin;} in the error rule's
action.
For example, suppose that on a syntax 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 look-ahead token ought to be discarded
+probably correct. The previous lookahead token ought to be discarded
with @samp{yyclearin;}.
@vindex YYRECOVERING
symbol (here, @code{exp}). When the parser returns to this state right
after having reduced a rule that produced an @code{exp}, the control
flow jumps to state 2. If there is no such transition on a nonterminal
-symbol, and the look-ahead is a @code{NUM}, then this token is shifted on
+symbol, and the lookahead is a @code{NUM}, then this token is shifted on
the parse stack, and the control flow jumps to state 1. Any other
-look-ahead triggers a syntax error.''
+lookahead triggers a syntax error.''
@cindex core, item set
@cindex item set core
@cindex kernel, item set
@cindex item set core
Even though the only active rule in state 0 seems to be rule 0, the
-report lists @code{NUM} as a look-ahead token because @code{NUM} can be
+report lists @code{NUM} as a lookahead token because @code{NUM} can be
at the beginning of any rule deriving an @code{exp}. By default Bison
reports the so-called @dfn{core} or @dfn{kernel} of the item set, but if
you want to see more detail you can invoke @command{bison} with
@end example
@noindent
-the rule 5, @samp{exp: NUM;}, is completed. Whatever the look-ahead token
+the rule 5, @samp{exp: NUM;}, is completed. Whatever the lookahead token
(@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}).
@noindent
In state 2, the automaton can only shift a symbol. For instance,
-because of the item @samp{exp -> exp . '+' exp}, if the look-ahead if
+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 4, corresponding to the item @samp{exp -> exp
'+' . exp}. Since there is no default action, any other token than
$default reduce using rule 1 (exp)
@end example
-Indeed, there are two actions associated to the look-ahead @samp{/}:
+Indeed, there are two actions associated to the lookahead @samp{/}:
either shifting (and going to state 7), 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
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 look-ahead is required to select the action. State 8 is
-one such state: if the look-ahead is @samp{*} or @samp{/} then the action
+possible, the lookahead is required to select the action. State 8 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
-look-ahead token is @samp{*}, since we specified that @samp{*} has higher
+lookahead token is @samp{*}, since we specified that @samp{*} has higher
precedence than @samp{+}. More generally, some items are eligible only
-with some set of possible look-ahead tokens. When run with
-@option{--report=look-ahead}, Bison specifies these look-ahead tokens:
+with some set of possible lookahead tokens. When run with
+@option{--report=lookahead}, Bison specifies these lookahead tokens:
@example
state 8
Description of the grammar, conflicts (resolved and unresolved), and
@acronym{LALR} automaton.
-@item look-ahead
+@item lookahead
Implies @code{state} and augments the description of the automaton with
-each rule's look-ahead set.
+each rule's lookahead set.
@item itemset
Implies @code{state} and augments the description of the automaton with
grammar rules so as to allow the Bison parser to recognize an error in
the grammar without halting the process. In effect, a sentence
containing an error may be recognized as valid. On a syntax error, the
-token @code{error} becomes the current look-ahead token. Actions
-corresponding to @code{error} are then executed, and the look-ahead
+token @code{error} becomes the current lookahead token. Actions
+corresponding to @code{error} are then executed, and the lookahead
token is reset to the token that originally caused the violation.
@xref{Error Recovery}.
@end deffn
@end deffn
@deffn {Macro} YYBACKUP
-Macro to discard a value from the parser stack and fake a look-ahead
+Macro to discard a value from the parser stack and fake a lookahead
token. @xref{Action Features, ,Special Features for Use in Actions}.
@end deffn
@deffn {Variable} yychar
External integer variable that contains the integer value of the
-look-ahead token. (In a pure parser, it is a local variable within
+lookahead token. (In a pure parser, it is a local variable within
@code{yyparse}.) Error-recovery rule actions may examine this variable.
@xref{Action Features, ,Special Features for Use in Actions}.
@end deffn
@deffn {Variable} yyclearin
Macro used in error-recovery rule actions. It clears the previous
-look-ahead token. @xref{Error Recovery}.
+lookahead token. @xref{Error Recovery}.
@end deffn
@deffn {Macro} YYDEBUG
You can ignore this variable if you don't use the @samp{@@} feature in the
grammar actions.
@xref{Token Locations, ,Textual Locations of Tokens}.
-In semantic actions, it stores the location of the look-ahead token.
+In semantic actions, it stores the location of the lookahead token.
@xref{Actions and Locations, ,Actions and Locations}.
@end deffn
variable within @code{yyparse}, and its address is passed to
@code{yylex}.)
@xref{Token Values, ,Semantic Values of Tokens}.
-In semantic actions, it stores the semantic value of the look-ahead token.
+In semantic actions, it stores the semantic value of the lookahead token.
@xref{Actions, ,Actions}.
@end deffn
@item Literal string token
A token which consists of two or more fixed characters. @xref{Symbols}.
-@item Look-ahead token
-A token already read but not yet shifted. @xref{Look-Ahead, ,Look-Ahead
+@item Lookahead token
+A token already read but not yet shifted. @xref{Lookahead, ,Lookahead
Tokens}.
@item @acronym{LALR}(1)
@item @acronym{LR}(1)
The class of context-free grammars in which at most one token of
-look-ahead is needed to disambiguate the parsing of any piece of input.
+lookahead is needed to disambiguate the parsing of any piece of input.
@item Nonterminal symbol
A grammar symbol standing for a grammatical construct that can
-/* Find and resolve or report look-ahead conflicts for bison,
+/* Find and resolve or report lookahead conflicts for bison,
Copyright (C) 1984, 1989, 1992, 2000, 2001, 2002, 2003, 2004, 2005, 2006
Free Software Foundation, Inc.
static struct obstack solved_conflicts_obstack;
static bitset shift_set;
-static bitset look_ahead_set;
+static bitset lookahead_set;
\f
transitions *trans = s->transitions;
int i;
- bitset_reset (look_ahead_set, token);
+ bitset_reset (lookahead_set, token);
for (i = 0; i < trans->num; i++)
if (!TRANSITION_IS_DISABLED (trans, i)
&& TRANSITION_SYMBOL (trans, i) == token)
/*--------------------------------------------------------------------.
| Turn off the reduce recorded for the specified token for the |
-| specified look-ahead. Used when we resolve a shift-reduce conflict |
+| specified lookahead. Used when we resolve a shift-reduce conflict |
| in favor of the shift. |
`--------------------------------------------------------------------*/
static void
-flush_reduce (bitset look_ahead_tokens, int token)
+flush_reduce (bitset lookahead_tokens, int token)
{
- bitset_reset (look_ahead_tokens, token);
+ bitset_reset (lookahead_tokens, token);
}
| rule has a precedence. A conflict is resolved by modifying the |
| shift or reduce tables so that there is no longer a conflict. |
| |
-| RULENO is the number of the look-ahead bitset to consider. |
+| RULENO is the number of the lookahead bitset to consider. |
| |
| ERRORS can be used to store discovered explicit errors. |
`------------------------------------------------------------------*/
/* Find the rule to reduce by to get precedence of reduction. */
rule *redrule = reds->rules[ruleno];
int redprec = redrule->prec->prec;
- bitset look_ahead_tokens = reds->look_ahead_tokens[ruleno];
+ bitset lookahead_tokens = reds->lookahead_tokens[ruleno];
int nerrs = 0;
for (i = 0; i < ntokens; i++)
- if (bitset_test (look_ahead_tokens, i)
- && bitset_test (look_ahead_set, i)
+ if (bitset_test (lookahead_tokens, i)
+ && bitset_test (lookahead_set, i)
&& symbols[i]->prec)
{
/* Shift-reduce conflict occurs for token number i
else if (symbols[i]->prec > redprec)
{
log_resolution (redrule, i, shift_resolution);
- flush_reduce (look_ahead_tokens, i);
+ flush_reduce (lookahead_tokens, i);
}
else
/* Matching precedence levels.
case right_assoc:
log_resolution (redrule, i, right_resolution);
- flush_reduce (look_ahead_tokens, i);
+ flush_reduce (lookahead_tokens, i);
break;
case left_assoc:
case non_assoc:
log_resolution (redrule, i, nonassoc_resolution);
flush_shift (s, i);
- flush_reduce (look_ahead_tokens, i);
+ flush_reduce (lookahead_tokens, i);
/* Record an explicit error for this token. */
errors[nerrs++] = symbols[i];
break;
| Solve the S/R conflicts of state S using the |
| precedence/associativity, and flag it inconsistent if it still has |
| conflicts. ERRORS can be used as storage to compute the list of |
-| look-ahead tokens on which S raises a syntax error (%nonassoc). |
+| lookahead tokens on which S raises a syntax error (%nonassoc). |
`-------------------------------------------------------------------*/
static void
if (s->consistent)
return;
- bitset_zero (look_ahead_set);
+ bitset_zero (lookahead_set);
FOR_EACH_SHIFT (trans, i)
- bitset_set (look_ahead_set, TRANSITION_SYMBOL (trans, i));
+ bitset_set (lookahead_set, TRANSITION_SYMBOL (trans, i));
- /* Loop over all rules which require look-ahead in this state. First
+ /* Loop over all rules which require lookahead in this state. First
check for shift-reduce conflict, and try to resolve using
precedence. */
for (i = 0; i < reds->num; ++i)
if (reds->rules[i]->prec && reds->rules[i]->prec->prec
- && !bitset_disjoint_p (reds->look_ahead_tokens[i], look_ahead_set))
+ && !bitset_disjoint_p (reds->lookahead_tokens[i], lookahead_set))
resolve_sr_conflict (s, i, errors);
- /* Loop over all rules which require look-ahead in this state. Check
+ /* Loop over all rules which require lookahead in this state. Check
for conflicts not resolved above. */
for (i = 0; i < reds->num; ++i)
{
- if (!bitset_disjoint_p (reds->look_ahead_tokens[i], look_ahead_set))
+ if (!bitset_disjoint_p (reds->lookahead_tokens[i], lookahead_set))
conflicts[s->number] = 1;
- bitset_or (look_ahead_set, look_ahead_set, reds->look_ahead_tokens[i]);
+ bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
}
}
conflicts_solve (void)
{
state_number i;
- /* List of look-ahead tokens on which we explicitly raise a syntax error. */
+ /* List of lookahead tokens on which we explicitly raise a syntax error. */
symbol **errors = xnmalloc (ntokens + 1, sizeof *errors);
conflicts = xcalloc (nstates, sizeof *conflicts);
shift_set = bitset_create (ntokens, BITSET_FIXED);
- look_ahead_set = bitset_create (ntokens, BITSET_FIXED);
+ lookahead_set = bitset_create (ntokens, BITSET_FIXED);
obstack_init (&solved_conflicts_obstack);
for (i = 0; i < nstates; i++)
if (!trans)
return 0;
- bitset_zero (look_ahead_set);
+ bitset_zero (lookahead_set);
bitset_zero (shift_set);
FOR_EACH_SHIFT (trans, i)
bitset_set (shift_set, TRANSITION_SYMBOL (trans, i));
for (i = 0; i < reds->num; ++i)
- bitset_or (look_ahead_set, look_ahead_set, reds->look_ahead_tokens[i]);
+ bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
- bitset_and (look_ahead_set, look_ahead_set, shift_set);
+ bitset_and (lookahead_set, lookahead_set, shift_set);
- src_count = bitset_count (look_ahead_set);
+ src_count = bitset_count (lookahead_set);
return src_count;
}
int count = 0;
int j;
for (j = 0; j < reds->num; ++j)
- if (bitset_test (reds->look_ahead_tokens[j], i))
+ if (bitset_test (reds->lookahead_tokens[j], i))
count++;
if (count >= 2)
/*--------------------------------------------------------.
| Total the number of S/R and R/R conflicts. Unlike the |
| code in conflicts_output, however, count EACH pair of |
-| reductions for the same state and look-ahead as one |
+| reductions for the same state and lookahead as one |
| conflict. |
`--------------------------------------------------------*/
{
free (conflicts);
bitset_free (shift_set);
- bitset_free (look_ahead_set);
+ bitset_free (lookahead_set);
obstack_free (&solved_conflicts_obstack, NULL);
}
-/* Find and resolve or report look-ahead conflicts for bison,
+/* Find and resolve or report lookahead conflicts for bison,
Copyright (C) 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
"none",
"state", "states",
"itemset", "itemsets",
- "look-ahead", "lookahead", "lookaheads",
+ "lookahead", "lookaheads", "look-ahead",
"solved",
"all",
0
report_none,
report_states, report_states,
report_states | report_itemsets, report_states | report_itemsets,
- report_states | report_look_ahead_tokens,
- report_states | report_look_ahead_tokens,
- report_states | report_look_ahead_tokens,
+ report_states | report_lookahead_tokens,
+ report_states | report_lookahead_tokens,
+ report_states | report_lookahead_tokens,
report_states | report_solved_conflicts,
report_all
};
THINGS is a list of comma separated words that can include:\n\
`state' describe the states\n\
`itemset' complete the core item sets with their closure\n\
- `look-ahead' explicitly associate look-ahead tokens to items\n\
+ `lookahead' explicitly associate lookahead tokens to items\n\
`solved' describe shift/reduce conflicts solving\n\
`all' include all the above information\n\
`none' disable the report\n\
report_none = 0,
report_states = 1 << 0,
report_itemsets = 1 << 1,
- report_look_ahead_tokens= 1 << 2,
+ report_lookahead_tokens = 1 << 2,
report_solved_conflicts = 1 << 3,
report_all = ~0
};
-/* Compute look-ahead criteria for Bison.
+/* Compute lookahead criteria for Bison.
Copyright (C) 1984, 1986, 1989, 2000, 2001, 2002, 2003, 2004, 2005,
2006 Free Software Foundation, Inc.
/* Compute how to make the finite state machine deterministic; find
- which rules need look-ahead in each state, and which look-ahead
+ which rules need lookahead in each state, and which lookahead
tokens they accept. */
#include <config.h>
{
int ri = state_reduction_find (s, r);
goto_list *sp = xmalloc (sizeof *sp);
- sp->next = lookback[(s->reductions->look_ahead_tokens - LA) + ri];
+ sp->next = lookback[(s->reductions->lookahead_tokens - LA) + ri];
sp->value = gotono;
- lookback[(s->reductions->look_ahead_tokens - LA) + ri] = sp;
+ lookback[(s->reductions->lookahead_tokens - LA) + ri] = sp;
}
static void
-compute_look_ahead_tokens (void)
+compute_lookahead_tokens (void)
{
size_t i;
goto_list *sp;
}
-/*-----------------------------------------------------.
-| Count the number of look-ahead tokens required for S |
-| (N_LOOK_AHEAD_TOKENS member). |
-`-----------------------------------------------------*/
+/*----------------------------------------------------.
+| Count the number of lookahead tokens required for S |
+| (N_LOOKAHEAD_TOKENS member). |
+`----------------------------------------------------*/
static int
-state_look_ahead_tokens_count (state *s)
+state_lookahead_tokens_count (state *s)
{
int k;
- int n_look_ahead_tokens = 0;
+ int n_lookahead_tokens = 0;
reductions *rp = s->reductions;
transitions *sp = s->transitions;
- /* We need a look-ahead either to distinguish different
+ /* We need a lookahead either to distinguish different
reductions (i.e., there are two or more), or to distinguish a
reduction from a shift. Otherwise, it is straightforward,
and the state is `consistent'. */
if (rp->num > 1
|| (rp->num == 1 && sp->num &&
!TRANSITION_IS_DISABLED (sp, 0) && TRANSITION_IS_SHIFT (sp, 0)))
- n_look_ahead_tokens += rp->num;
+ n_lookahead_tokens += rp->num;
else
s->consistent = 1;
break;
}
- return n_look_ahead_tokens;
+ return n_lookahead_tokens;
}
-/*-----------------------------------------------------.
-| Compute LA, NLA, and the look_ahead_tokens members. |
-`-----------------------------------------------------*/
+/*----------------------------------------------------.
+| Compute LA, NLA, and the lookahead_tokens members. |
+`----------------------------------------------------*/
static void
initialize_LA (void)
state_number i;
bitsetv pLA;
- /* Compute the total number of reductions requiring a look-ahead. */
+ /* Compute the total number of reductions requiring a lookahead. */
nLA = 0;
for (i = 0; i < nstates; i++)
- nLA += state_look_ahead_tokens_count (states[i]);
+ nLA += state_lookahead_tokens_count (states[i]);
/* Avoid having to special case 0. */
if (!nLA)
nLA = 1;
pLA = LA = bitsetv_create (nLA, ntokens, BITSET_FIXED);
lookback = xcalloc (nLA, sizeof *lookback);
- /* Initialize the members LOOK_AHEAD_TOKENS for each state whose reductions
- require look-ahead tokens. */
+ /* Initialize the members LOOKAHEAD_TOKENS for each state whose reductions
+ require lookahead tokens. */
for (i = 0; i < nstates; i++)
{
- int count = state_look_ahead_tokens_count (states[i]);
+ int count = state_lookahead_tokens_count (states[i]);
if (count)
{
- states[i]->reductions->look_ahead_tokens = pLA;
+ states[i]->reductions->lookahead_tokens = pLA;
pLA += count;
}
}
}
-/*----------------------------------------------.
-| Output the look-ahead tokens for each state. |
-`----------------------------------------------*/
+/*---------------------------------------------.
+| Output the lookahead tokens for each state. |
+`---------------------------------------------*/
static void
-look_ahead_tokens_print (FILE *out)
+lookahead_tokens_print (FILE *out)
{
state_number i;
int j, k;
- fprintf (out, "Look-ahead tokens: BEGIN\n");
+ fprintf (out, "Lookahead tokens: BEGIN\n");
for (i = 0; i < nstates; ++i)
{
reductions *reds = states[i]->reductions;
bitset_iterator iter;
- int n_look_ahead_tokens = 0;
+ int n_lookahead_tokens = 0;
- if (reds->look_ahead_tokens)
+ if (reds->lookahead_tokens)
for (k = 0; k < reds->num; ++k)
- if (reds->look_ahead_tokens[k])
- ++n_look_ahead_tokens;
+ if (reds->lookahead_tokens[k])
+ ++n_lookahead_tokens;
- fprintf (out, "State %d: %d look-ahead tokens\n",
- i, n_look_ahead_tokens);
+ fprintf (out, "State %d: %d lookahead tokens\n",
+ i, n_lookahead_tokens);
- if (reds->look_ahead_tokens)
+ if (reds->lookahead_tokens)
for (j = 0; j < reds->num; ++j)
- BITSET_FOR_EACH (iter, reds->look_ahead_tokens[j], k, 0)
+ BITSET_FOR_EACH (iter, reds->lookahead_tokens[j], k, 0)
{
fprintf (out, " on %d (%s) -> rule %d\n",
k, symbols[k]->tag,
reds->rules[j]->number);
};
}
- fprintf (out, "Look-ahead tokens: END\n");
+ fprintf (out, "Lookahead tokens: END\n");
}
void
initialize_F ();
build_relations ();
compute_FOLLOWS ();
- compute_look_ahead_tokens ();
+ compute_lookahead_tokens ();
if (trace_flag & trace_sets)
- look_ahead_tokens_print (stderr);
+ lookahead_tokens_print (stderr);
}
{
state_number s;
for (s = 0; s < nstates; ++s)
- states[s]->reductions->look_ahead_tokens = NULL;
+ states[s]->reductions->lookahead_tokens = NULL;
bitsetv_free (LA);
}
-/* Compute look-ahead criteria for bison,
+/* Compute lookahead criteria for bison,
Copyright (C) 1984, 1986, 1989, 2000, 2002, 2004 Free Software
Foundation, Inc.
# include "state.h"
/* Compute how to make the finite state machine deterministic; find
- which rules need look-ahead in each state, and which look-ahead
+ which rules need lookahead in each state, and which lookahead
tokens they accept. */
void lalr (void);
-/* Release the information related to look-ahead tokens. Can be performed
+/* Release the information related to lookahead tokens. Can be performed
once the action tables are computed. */
void lalr_free (void);
timevar_pop (TV_LALR);
/* Find and record any conflicts: places where one token of
- look-ahead is not enough to disambiguate the parsing. In file
+ lookahead is not enough to disambiguate the parsing. In file
conflicts. Also resolve s/r conflicts based on precedence
declarations. */
timevar_push (TV_CONFLICTS);
if (complaint_issued)
goto finish;
- /* Look-ahead tokens are no longer needed. */
+ /* Lookahead tokens are no longer needed. */
timevar_push (TV_FREE);
lalr_free ();
timevar_pop (TV_FREE);
prepare_actions (void)
{
/* Figure out the actions for the specified state, indexed by
- look-ahead token type. */
+ lookahead token type. */
muscle_insert_rule_number_table ("defact", yydefact,
yydefact[0], 1, nstates);
#endif
#endif
{
- /* The look-ahead symbol. */
+ /* The lookahead symbol. */
int yychar;
-/* The semantic value of the look-ahead symbol. */
+/* The semantic value of the lookahead symbol. */
YYSTYPE yylval;
/* Number of syntax errors so far. */
int yynerrs;
-/* Location data for the look-ahead symbol. */
+/* Location data for the lookahead symbol. */
YYLTYPE yylloc;
int yystate;
int yyresult;
/* Number of tokens to shift before error messages enabled. */
int yyerrstatus;
- /* Look-ahead token as an internal (translated) token number. */
+ /* Lookahead token as an internal (translated) token number. */
int yytoken = 0;
#if YYERROR_VERBOSE
/* Buffer for error messages, and its allocated size. */
yybackup:
/* Do appropriate processing given the current state. Read a
- look-ahead token if we need one and don't already have one. */
+ lookahead token if we need one and don't already have one. */
- /* First try to decide what to do without reference to look-ahead token. */
+ /* First try to decide what to do without reference to lookahead token. */
yyn = yypact[yystate];
if (yyn == YYPACT_NINF)
goto yydefault;
- /* Not known => get a look-ahead token if don't already have one. */
+ /* Not known => get a lookahead token if don't already have one. */
- /* YYCHAR is either YYEMPTY or YYEOF or a valid look-ahead symbol. */
+ /* YYCHAR is either YYEMPTY or YYEOF or a valid lookahead symbol. */
if (yychar == YYEMPTY)
{
YYDPRINTF ((stderr, "Reading a token: "));
if (yyerrstatus)
yyerrstatus--;
- /* Shift the look-ahead token. */
+ /* Shift the lookahead token. */
YY_SYMBOL_PRINT ("Shifting", yytoken, &yylval, &yylloc);
/* Discard the shifted token unless it is eof. */
if (yyerrstatus == 3)
{
- /* If just tried and failed to reuse look-ahead token after an
+ /* If just tried and failed to reuse lookahead token after an
error, discard it. */
if (yychar <= YYEOF)
}
}
- /* Else will try to reuse look-ahead token after shifting the error
+ /* Else will try to reuse lookahead token after shifting the error
token. */
goto yyerrlab1;
yyerror_range[1] = yylloc;
/* Using YYLLOC is tempting, but would change the location of
- the look-ahead. YYLOC is available though. */
+ the lookahead. YYLOC is available though. */
YYLLOC_DEFAULT (yyloc, (yyerror_range - 1), 2);
*++yylsp = yyloc;
#include "symtab.h"
static bitset shift_set;
-static bitset look_ahead_set;
+static bitset lookahead_set;
#if 0
static void
for (/* Nothing */; *sp >= 0; ++sp)
fprintf (out, " %s", symbols[*sp]->tag);
- /* Display the look-ahead tokens? */
- if (report_flag & report_look_ahead_tokens)
- state_rule_look_ahead_tokens_print (s, &rules[r], out);
+ /* Display the lookahead tokens? */
+ if (report_flag & report_lookahead_tokens)
+ state_rule_lookahead_tokens_print (s, &rules[r], out);
fputc ('\n', out);
}
size_t width = 0;
int i;
- /* Compute the width of the look-ahead token column. */
+ /* Compute the width of the lookahead token column. */
for (i = 0; i < trans->num; i++)
if (!TRANSITION_IS_DISABLED (trans, i)
&& TRANSITION_IS_SHIFT (trans, i) == display_transitions_p)
fputc ('\n', out);
width += 2;
- /* Report look-ahead tokens and shifts. */
+ /* Report lookahead tokens and shifts. */
for (i = 0; i < trans->num; i++)
if (!TRANSITION_IS_DISABLED (trans, i)
&& TRANSITION_IS_SHIFT (trans, i) == display_transitions_p)
size_t width = 0;
int i;
- /* Compute the width of the look-ahead token column. */
+ /* Compute the width of the lookahead token column. */
for (i = 0; i < errp->num; ++i)
if (errp->symbols[i])
max_length (&width, errp->symbols[i]->tag);
fputc ('\n', out);
width += 2;
- /* Report look-ahead tokens and errors. */
+ /* Report lookahead tokens and errors. */
for (i = 0; i < errp->num; ++i)
if (errp->symbols[i])
{
int cmax = 0;
int i;
- /* No need for a look-ahead. */
+ /* No need for a lookahead. */
if (s->consistent)
return reds->rules[0];
- /* 1. Each reduction is possibly masked by the look-ahead tokens on which
+ /* 1. Each reduction is possibly masked by the lookahead tokens on which
we shift (S/R conflicts)... */
bitset_zero (shift_set);
{
}
}
- /* 2. Each reduction is possibly masked by the look-ahead tokens on which
+ /* 2. Each reduction is possibly masked by the lookahead tokens on which
we raise an error (due to %nonassoc). */
{
errs *errp = s->errs;
{
int count = 0;
- /* How many non-masked look-ahead tokens are there for this
+ /* How many non-masked lookahead tokens are there for this
reduction? */
- bitset_andn (look_ahead_set, reds->look_ahead_tokens[i], shift_set);
- count = bitset_count (look_ahead_set);
+ bitset_andn (lookahead_set, reds->lookahead_tokens[i], shift_set);
+ count = bitset_count (lookahead_set);
if (count > cmax)
{
/* 3. And finally, each reduction is possibly masked by previous
reductions (in R/R conflicts, we keep the first reductions).
*/
- bitset_or (shift_set, shift_set, reds->look_ahead_tokens[i]);
+ bitset_or (shift_set, shift_set, reds->lookahead_tokens[i]);
}
return default_rule;
}
-/*--------------------------------------------------------------------------.
-| Report a reduction of RULE on LOOK_AHEAD_TOKEN (which can be `default'). |
-| If not ENABLED, the rule is masked by a shift or a reduce (S/R and |
-| R/R conflicts). |
-`--------------------------------------------------------------------------*/
+/*-------------------------------------------------------------------------.
+| Report a reduction of RULE on LOOKAHEAD_TOKEN (which can be `default'). |
+| If not ENABLED, the rule is masked by a shift or a reduce (S/R and |
+| R/R conflicts). |
+`-------------------------------------------------------------------------*/
static void
print_reduction (FILE *out, size_t width,
- const char *look_ahead_token,
+ const char *lookahead_token,
rule *r, bool enabled)
{
int j;
- fprintf (out, " %s", look_ahead_token);
- for (j = width - strlen (look_ahead_token); j > 0; --j)
+ fprintf (out, " %s", lookahead_token);
+ for (j = width - strlen (lookahead_token); j > 0; --j)
fputc (' ', out);
if (!enabled)
fputc ('[', out);
FOR_EACH_SHIFT (trans, i)
bitset_set (shift_set, TRANSITION_SYMBOL (trans, i));
- /* Compute the width of the look-ahead token column. */
+ /* Compute the width of the lookahead token column. */
if (default_rule)
width = strlen (_("$default"));
- if (reds->look_ahead_tokens)
+ if (reds->lookahead_tokens)
for (i = 0; i < ntokens; i++)
{
bool count = bitset_test (shift_set, i);
for (j = 0; j < reds->num; ++j)
- if (bitset_test (reds->look_ahead_tokens[j], i))
+ if (bitset_test (reds->lookahead_tokens[j], i))
{
if (! count)
{
fputc ('\n', out);
width += 2;
- /* Report look-ahead tokens (or $default) and reductions. */
- if (reds->look_ahead_tokens)
+ /* Report lookahead tokens (or $default) and reductions. */
+ if (reds->lookahead_tokens)
for (i = 0; i < ntokens; i++)
{
bool defaulted = false;
bool count = bitset_test (shift_set, i);
for (j = 0; j < reds->num; ++j)
- if (bitset_test (reds->look_ahead_tokens[j], i))
+ if (bitset_test (reds->lookahead_tokens[j], i))
{
if (! count)
{
new_closure (nritems);
/* Storage for print_reductions. */
shift_set = bitset_create (ntokens, BITSET_FIXED);
- look_ahead_set = bitset_create (ntokens, BITSET_FIXED);
+ lookahead_set = bitset_create (ntokens, BITSET_FIXED);
for (i = 0; i < nstates; i++)
print_state (out, states[i]);
bitset_free (shift_set);
- bitset_free (look_ahead_set);
+ bitset_free (lookahead_set);
if (report_flag & report_itemsets)
free_closure ();
for (/* Nothing */; *sp >= 0; ++sp)
obstack_fgrow1 (oout, " %s", symbols[*sp]->tag);
- /* Experimental feature: display the look-ahead tokens. */
- if (report_flag & report_look_ahead_tokens)
+ /* Experimental feature: display the lookahead tokens. */
+ if (report_flag & report_lookahead_tokens)
{
/* Find the reduction we are handling. */
reductions *reds = s->reductions;
int redno = state_reduction_find (s, &rules[r]);
/* Print them if there are. */
- if (reds->look_ahead_tokens && redno != -1)
+ if (reds->lookahead_tokens && redno != -1)
{
bitset_iterator biter;
int k;
char const *sep = "";
obstack_sgrow (oout, "[");
- BITSET_FOR_EACH (biter, reds->look_ahead_tokens[redno], k, 0)
+ BITSET_FOR_EACH (biter, reds->lookahead_tokens[redno], k, 0)
{
obstack_fgrow2 (oout, "%s%s", sep, symbols[k]->tag);
sep = ", ";
size_t rules_size = num * sizeof *reds;
reductions *res = xmalloc (offsetof (reductions, rules) + rules_size);
res->num = num;
- res->look_ahead_tokens = NULL;
+ res->lookahead_tokens = NULL;
memcpy (res->rules, reds, rules_size);
return res;
}
-/*---------------------------------------------------.
-| Print on OUT all the look-ahead tokens such that S |
-| wants to reduce R. |
-`---------------------------------------------------*/
+/*--------------------------------------------------.
+| Print on OUT all the lookahead tokens such that S |
+| wants to reduce R. |
+`--------------------------------------------------*/
void
-state_rule_look_ahead_tokens_print (state *s, rule *r, FILE *out)
+state_rule_lookahead_tokens_print (state *s, rule *r, FILE *out)
{
/* Find the reduction we are handling. */
reductions *reds = s->reductions;
int red = state_reduction_find (s, r);
/* Print them if there are. */
- if (reds->look_ahead_tokens && red != -1)
+ if (reds->lookahead_tokens && red != -1)
{
bitset_iterator biter;
int k;
char const *sep = "";
fprintf (out, " [");
- BITSET_FOR_EACH (biter, reds->look_ahead_tokens[red], k, 0)
+ BITSET_FOR_EACH (biter, reds->lookahead_tokens[red], k, 0)
{
fprintf (out, "%s%s", sep, symbols[k]->tag);
sep = ", ";
Each core contains a vector of NITEMS items which are the indices
in the RITEMS vector of the items that are selected in this state.
- The two types of actions are shifts/gotos (push the look-ahead token
+ The two types of actions are shifts/gotos (push the lookahead token
and read another/goto to the state designated by a nterm) and
reductions (combine the last n things on the stack via a rule,
replace them with the symbol that the rule derives, and leave the
- look-ahead token alone). When the states are generated, these
+ lookahead token alone). When the states are generated, these
actions are represented in two other lists.
Each transition structure describes the possible transitions out
typedef struct
{
int num;
- bitset *look_ahead_tokens;
+ bitset *lookahead_tokens;
rule *rules[1];
} reductions;
reductions *reductions;
errs *errs;
- /* Nonzero if no look-ahead is needed to decide what to do in state S. */
+ /* Nonzero if no lookahead is needed to decide what to do in state S. */
char consistent;
/* If some conflicts were solved thanks to precedence/associativity,
/* Set the errs of STATE. */
void state_errs_set (state *s, int num, symbol **errors);
-/* Print on OUT all the look-ahead tokens such that this STATE wants to
+/* Print on OUT all the lookahead tokens such that this STATE wants to
reduce R. */
-void state_rule_look_ahead_tokens_print (state *s, rule *r, FILE *out);
+void state_rule_lookahead_tokens_print (state *s, rule *r, FILE *out);
/* Create/destroy the states hash table. */
void state_hash_new (void);
/* Find all reductions for token J, and record all that do not
match ACTROW[J]. */
for (i = 0; i < reds->num; i += 1)
- if (bitset_test (reds->look_ahead_tokens[i], j)
+ if (bitset_test (reds->lookahead_tokens[i], j)
&& (actrow[j]
!= rule_number_as_item_number (reds->rules[i]->number)))
{
/*------------------------------------------------------------------.
| Decide what to do for each type of token if seen as the |
-| look-ahead in specified state. The value returned is used as the |
+| lookahead in specified state. The value returned is used as the |
| default action (yydefact) for the state. In addition, ACTROW is |
| filled with what to do for each kind of token, index by symbol |
| number, with zero meaning do the default action. The value |
| situation is an error. The parser recognizes this value |
| specially. |
| |
-| This is where conflicts are resolved. The loop over look-ahead |
+| This is where conflicts are resolved. The loop over lookahead |
| rules considered lower-numbered rules last, and the last rule |
| considered that likes a token gets to handle it. |
| |
for (i = 0; i < ntokens; i++)
actrow[i] = conflrow[i] = 0;
- if (reds->look_ahead_tokens)
+ if (reds->lookahead_tokens)
{
int j;
bitset_iterator biter;
/* loop over all the rules available here which require
- look-ahead (in reverse order to give precedence to the first
+ lookahead (in reverse order to give precedence to the first
rule) */
for (i = reds->num - 1; i >= 0; --i)
/* and find each token which the rule finds acceptable
to come next */
- BITSET_FOR_EACH (biter, reds->look_ahead_tokens[i], j, 0)
+ BITSET_FOR_EACH (biter, reds->lookahead_tokens[i], j, 0)
{
/* and record this rule as the rule to use if that
token follows. */
/*------------------------------------------------------------------.
| Figure out the actions for the specified state, indexed by |
-| look-ahead token type. |
+| lookahead token type. |
| |
| The YYDEFACT table is output now. The detailed info is saved for |
| putting into YYTABLE later. |
something else to do.
YYPACT[S] = index in YYTABLE of the portion describing state S.
- The look-ahead token's type is used to index that portion to find
+ The lookahead token's type is used to index that portion to find
out what to do.
If the value in YYTABLE is positive, we shift the token and go to
#
# - test the action associated to `error'
#
-# - check the look-ahead that triggers an error is not discarded
-# when we enter error recovery. Below, the look-ahead causing the
+# - check the lookahead that triggers an error is not discarded
+# when we enter error recovery. Below, the lookahead causing the
# first error is ")", which is needed to recover from the error and
# produce the "0" that triggers the "0 != 1" error.
#
calc: error: 4444 != 1])
# The same, but this time exercising explicitly triggered syntax errors.
-# POSIX says the look-ahead causing the error should not be discarded.
+# POSIX says the lookahead causing the error should not be discarded.
_AT_CHECK_CALC_ERROR([$1], [0], [(!) + (0 0) = 1], [102],
[1.9: syntax error, unexpected number
calc: error: 2222 != 1])
#include <stdio.h>
static void yyerror (char const *);
static int yylex (void);
- static void print_look_ahead (char const *);
+ static void print_lookahead (char const *);
#define USE(value)
%}
start:
defstate_init defstate_shift 'b' change_lookahead 'a' {
USE ($3);
- print_look_ahead ("start <- defstate_init defstate_shift 'b'");
+ print_lookahead ("start <- defstate_init defstate_shift 'b'");
}
;
defstate_init:
{
- print_look_ahead ("defstate_init <- empty string");
+ print_lookahead ("defstate_init <- empty string");
}
;
defstate_shift:
nondefstate defstate_look 'a' {
USE ($3);
- print_look_ahead ("defstate_shift <- nondefstate defstate_look 'a'");
+ print_lookahead ("defstate_shift <- nondefstate defstate_look 'a'");
}
;
defstate_look:
{
- print_look_ahead ("defstate_look <- empty string");
+ print_lookahead ("defstate_look <- empty string");
}
;
nondefstate:
{
- print_look_ahead ("nondefstate <- empty string");
+ print_lookahead ("nondefstate <- empty string");
}
| 'b' {
USE ($1);
- print_look_ahead ("nondefstate <- 'b'");
+ print_lookahead ("nondefstate <- 'b'");
}
;
change_lookahead:
}
static void
-print_look_ahead (char const *reduction)
+print_lookahead (char const *reduction)
{
printf ("%s:\n yychar=", reduction);
if (yychar == YYEMPTY)
#include <stdio.h>
static void yyerror (char const *);
static int yylex (void);
- static void print_look_ahead (char const *);
+ static void print_lookahead (char const *);
static char merge (union YYSTYPE, union YYSTYPE);
#define USE(value)
%}
start:
merge 'c' stack_explosion {
USE ($2); USE ($3);
- print_look_ahead ("start <- merge 'c' stack_explosion");
+ print_lookahead ("start <- merge 'c' stack_explosion");
}
;
merge:
nonconflict1 'a' 'b' nonconflict2 %dprec 1 {
USE ($2); USE ($3);
- print_look_ahead ("merge <- nonconflict1 'a' 'b' nonconflict2");
+ print_lookahead ("merge <- nonconflict1 'a' 'b' nonconflict2");
}
| conflict defstate_look 'a' nonconflict2 'b' defstate_shift %dprec 2 {
USE ($3); USE ($5);
- print_look_ahead ("merge <- conflict defstate_look 'a' nonconflict2 'b'"
+ print_lookahead ("merge <- conflict defstate_look 'a' nonconflict2 'b'"
" defstate_shift");
}
;
nonconflict1:
{
- print_look_ahead ("nonconflict1 <- empty string");
+ print_lookahead ("nonconflict1 <- empty string");
}
;
nonconflict2:
{
- print_look_ahead ("nonconflict2 <- empty string");
+ print_lookahead ("nonconflict2 <- empty string");
}
| 'a' {
USE ($1);
- print_look_ahead ("nonconflict2 <- 'a'");
+ print_lookahead ("nonconflict2 <- 'a'");
}
;
conflict:
{
- print_look_ahead ("conflict <- empty string");
+ print_lookahead ("conflict <- empty string");
}
;
defstate_look:
{
- print_look_ahead ("defstate_look <- empty string");
+ print_lookahead ("defstate_look <- empty string");
}
;
/* yychar != YYEMPTY but lookahead need is yyfalse. */
defstate_shift:
{
- print_look_ahead ("defstate_shift <- empty string");
+ print_lookahead ("defstate_shift <- empty string");
}
;
}
static void
-print_look_ahead (char const *reduction)
+print_lookahead (char const *reduction)
{
printf ("%s:\n yychar=", reduction);
if (yychar == YYEMPTY)
-# AT_DATA_LOOK_AHEAD_TOKENS_GRAMMAR(FILE-NAME, SIZE)
+# AT_DATA_LOOKAHEAD_TOKENS_GRAMMAR(FILE-NAME, SIZE)
# --------------------------------------------------
# Create FILE-NAME, containing a self checking parser for a grammar
-# requiring SIZE look-ahead tokens.
-m4_define([AT_DATA_LOOK_AHEAD_TOKENS_GRAMMAR],
+# requiring SIZE lookahead tokens.
+m4_define([AT_DATA_LOOKAHEAD_TOKENS_GRAMMAR],
[AT_DATA([[gengram.pl]],
[[#! /usr/bin/perl -w
## ------------------------ ##
-## Many look-ahead tokens. ##
+## Many lookahead tokens. ##
## ------------------------ ##
-AT_SETUP([Many look-ahead tokens])
+AT_SETUP([Many lookahead tokens])
-AT_DATA_LOOK_AHEAD_TOKENS_GRAMMAR([input.y], [1000])
+AT_DATA_LOOKAHEAD_TOKENS_GRAMMAR([input.y], [1000])
# GNU m4 requires about 70 MiB for this test on a 32-bit host.
# Ask for 200 MiB, which should be plenty even on a 64-bit host.
projects / bison.git / commitdiff
