9.1 Bison Options

Bison supports both traditional single-letter options and mnemonic long option names. Long option names are indicated with ‘--’ instead of ‘-’. Abbreviations for option names are allowed as long as they are unique. When a long option takes an argument, like ‘--file-prefix’, connect the option name and the argument with ‘=’.

Here is a list of options that can be used with Bison, alphabetized by short option. It is followed by a cross key alphabetized by long option.

Operations modes:

‘-h’

‘--help’

Print a summary of the command-line options to Bison and exit.

‘-V’

‘--version’

Print the version number of Bison and exit.

‘--print-localedir’

Print the name of the directory containing locale-dependent data.

‘--print-datadir’

Print the name of the directory containing skeletons and XSLT.

‘-y’

‘--yacc’

Act more like the traditional Yacc command. This can cause different diagnostics to be generated, and may change behavior in other minor ways. Most importantly, imitate Yacc’s output file name conventions, so that the parser implementation file is called ‘y.tab.c’, and the other outputs are called ‘y.output’ and ‘y.tab.h’. Also, if generating a deterministic parser in C, generate #define statements in addition to an enum to associate token numbers with token names. Thus, the following shell script can substitute for Yacc, and the Bison distribution contains such a script for compatibility with POSIX:

#! /bin/sh
bison -y "$@"

The ‘-y’/‘--yacc’ option is intended for use with traditional Yacc grammars. If your grammar uses a Bison extension like ‘%glr-parser’, Bison might not be Yacc-compatible even if this option is specified.

‘-W [category]’

‘--warnings[=category]’

Output warnings falling in category. category can be one of:

midrule-values

Warn about mid-rule values that are set but not used within any of the actions of the parent rule. For example, warn about unused $2 in:

exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };

Also warn about mid-rule values that are used but not set. For example, warn about unset $$ in the mid-rule action in:

exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };

These warnings are not enabled by default since they sometimes prove to be false alarms in existing grammars employing the Yacc constructs $0 or $-n (where n is some positive integer).

yacc

Incompatibilities with POSIX Yacc.

conflicts-sr

conflicts-rr

S/R and R/R conflicts. These warnings are enabled by default. However, if the %expect or %expect-rr directive is specified, an unexpected number of conflicts is an error, and an expected number of conflicts is not reported, so ‘-W’ and ‘--warning’ then have no effect on the conflict report.

deprecated

Deprecated constructs whose support will be removed in future versions of Bison.

empty-rule

Empty rules without %empty. See section Empty Rules. Disabled by default, but enabled by uses of %empty, unless ‘-Wno-empty-rule’ was specified.

precedence

Useless precedence and associativity directives. Disabled by default.

Consider for instance the following grammar:

%nonassoc "="
%left "+"
%left "*"
%precedence "("

%%

stmt:
  exp
| "var" "=" exp
;

exp:
  exp "+" exp
| exp "*" "num"
| "(" exp ")"
| "num"
;

Bison reports:

warning: useless precedence and associativity for "="
 %nonassoc "="
           ^^^

warning: useless associativity for "*", use %precedence
 %left "*"
       ^^^

warning: useless precedence for "("
 %precedence "("
             ^^^

One would get the exact same parser with the following directives instead:

%left "+"
%precedence "*"

other

All warnings not categorized above. These warnings are enabled by default.

This category is provided merely for the sake of completeness. Future releases of Bison may move warnings from this category to new, more specific categories.

all

All the warnings except yacc.

none

Turn off all the warnings.

error

See ‘-Werror’, below.

A category can be turned off by prefixing its name with ‘no-’. For instance, ‘-Wno-yacc’ will hide the warnings about POSIX Yacc incompatibilities.

‘-Werror[=category]’

‘-Wno-error[=category]’

Enable warnings falling in category, and treat them as errors. If no category is given, it defaults to making all enabled warnings into errors.

category is the same as for ‘--warnings’, with the exception that it may not be prefixed with ‘no-’ (see above).

Prefixed with ‘no’, it deactivates the error treatment for this category. However, the warning itself won’t be disabled, or enabled, by this option.

Note that the precedence of the ‘=’ and ‘,’ operators is such that the following commands are not equivalent, as the first will not treat S/R conflicts as errors.

$ bison -Werror=yacc,conflicts-sr input.y
$ bison -Werror=yacc,error=conflicts-sr input.y

‘-f [feature]’

‘--feature[=feature]’

Activate miscellaneous feature. feature can be one of:

caret

diagnostics-show-caret

Show caret errors, in a manner similar to GCC’s ‘-fdiagnostics-show-caret’, or Clang’s ‘-fcaret-diagnotics’. The location provided with the message is used to quote the corresponding line of the source file, underlining the important part of it with carets (^). Here is an example, using the following file ‘in.y’:

%type <ival> exp
%%
exp: exp '+' exp { $exp = $1 + $2; };

When invoked with ‘-fcaret’ (or nothing), Bison will report:

in.y:3.20-23: error: ambiguous reference: '$exp'
 exp: exp '+' exp { $exp = $1 + $2; };
                    ^^^^

in.y:3.1-3:       refers to: $exp at $$
 exp: exp '+' exp { $exp = $1 + $2; };
 ^^^

in.y:3.6-8:       refers to: $exp at $1
 exp: exp '+' exp { $exp = $1 + $2; };
      ^^^

in.y:3.14-16:     refers to: $exp at $3
 exp: exp '+' exp { $exp = $1 + $2; };
              ^^^

in.y:3.32-33: error: $2 of 'exp' has no declared type
 exp: exp '+' exp { $exp = $1 + $2; };
                                ^^

Whereas, when invoked with ‘-fno-caret’, Bison will only report:

in.y:3.20-23: error: ambiguous reference: ‘$exp’
in.y:3.1-3:       refers to: $exp at $$
in.y:3.6-8:       refers to: $exp at $1
in.y:3.14-16:     refers to: $exp at $3
in.y:3.32-33: error: $2 of ‘exp’ has no declared type

This option is activated by default.

Tuning the parser:

‘-t’

‘--debug’

In the parser implementation file, define the macro YYDEBUG to 1 if it is not already defined, so that the debugging facilities are compiled. See section Tracing Your Parser.

‘-D name[=value]’

‘--define=name[=value]’

‘-F name[=value]’

‘--force-define=name[=value]’

Each of these is equivalent to ‘%define name "value"’ (see section %define Summary) except that Bison processes multiple definitions for the same name as follows:

• Bison quietly ignores all command-line definitions for name except the last.
• If that command-line definition is specified by a -D or --define, Bison reports an error for any %define definition for name.
• If that command-line definition is specified by a -F or --force-define instead, Bison quietly ignores all %define definitions for name.
• Otherwise, Bison reports an error if there are multiple %define definitions for name.

You should avoid using -F and --force-define in your make files unless you are confident that it is safe to quietly ignore any conflicting %define that may be added to the grammar file.

‘-L language’

‘--language=language’

Specify the programming language for the generated parser, as if %language was specified (see section Bison Declaration Summary). Currently supported languages include C, C++, and Java. language is case-insensitive.

‘--locations’

Pretend that %locations was specified. See section Bison Declaration Summary.

‘-p prefix’

‘--name-prefix=prefix’

Pretend that %name-prefix "prefix" was specified (see section Bison Declaration Summary). Obsoleted by -Dapi.prefix=prefix. See section Multiple Parsers in the Same Program.

‘-l’

‘--no-lines’

Don’t put any #line preprocessor commands in the parser implementation file. Ordinarily Bison puts them in the parser implementation file so that the C compiler and debuggers will associate errors with your source file, the grammar file. This option causes them to associate errors with the parser implementation file, treating it as an independent source file in its own right.

‘-S file’

‘--skeleton=file’

Specify the skeleton to use, similar to %skeleton (see section Bison Declaration Summary).

If file does not contain a /, file is the name of a skeleton file in the Bison installation directory. If it does, file is an absolute file name or a file name relative to the current working directory. This is similar to how most shells resolve commands.

‘-k’

‘--token-table’

Pretend that %token-table was specified. See section Bison Declaration Summary.

Adjust the output:

‘--defines[=file]’

Pretend that %defines was specified, i.e., write an extra output file containing macro definitions for the token type names defined in the grammar, as well as a few other declarations. See section Bison Declaration Summary.

‘-d’

This is the same as --defines except -d does not accept a file argument since POSIX Yacc requires that -d can be bundled with other short options.

‘-b file-prefix’

‘--file-prefix=prefix’

Pretend that %file-prefix was specified, i.e., specify prefix to use for all Bison output file names. See section Bison Declaration Summary.

‘-r things’

‘--report=things’

Write an extra output file containing verbose description of the comma separated list of things among:

state

Description of the grammar, conflicts (resolved and unresolved), and parser’s automaton.

itemset

Implies state and augments the description of the automaton with the full set of items for each state, instead of its core only.

lookahead

Implies state and augments the description of the automaton with each rule’s lookahead set.

solved

Implies state. Explain how conflicts were solved thanks to precedence and associativity directives.

all

Enable all the items.

none

Do not generate the report.

‘--report-file=file’

Specify the file for the verbose description.

‘-v’

‘--verbose’

Pretend that %verbose was specified, i.e., write an extra output file containing verbose descriptions of the grammar and parser. See section Bison Declaration Summary.

‘-o file’

‘--output=file’

Specify the file for the parser implementation file.

The other output files’ names are constructed from file as described under the ‘-v’ and ‘-d’ options.

‘-g [file]’

‘--graph[=file]’

Output a graphical representation of the parser’s automaton computed by Bison, in Graphviz DOT format. file is optional. If omitted and the grammar file is ‘foo.y’, the output file will be ‘foo.dot’.

‘-x [file]’

‘--xml[=file]’

Output an XML report of the parser’s automaton computed by Bison. file is optional. If omitted and the grammar file is ‘foo.y’, the output file will be ‘foo.xml’. (The current XML schema is experimental and may evolve. More user feedback will help to stabilize it.)

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