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Here is a table of Bison constructs, variables and macros that are useful in actions.
Acts like a variable that contains the semantic value for the grouping made by the current rule. See Actions.
Acts like a variable that contains the semantic value for the nth component of the current rule. See Actions.
Like
$$
but specifies alternative typealt in the union specified by the%union
declaration. See Data Types of Values in Actions.
Like
$
n but specifies alternative typealt in the union specified by the%union
declaration. See Data Types of Values in Actions.
Return immediately from
yyparse
, indicating failure. See The Parser Functionyyparse
.
Return immediately from
yyparse
, indicating success. See The Parser Functionyyparse
.
Unshift a token. This macro is allowed only for rules that reduce a single value, and only when there is no lookahead token. It is also disallowed in GLR parsers. It installs a lookahead token with token type token and semantic value 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 lookahead token already, then it reports a syntax error with a message ‘cannot back up’ and performs ordinary error recovery.
In either case, the rest of the action is not executed.
Cause an immediate syntax error. This statement initiates error recovery just as if the parser itself had detected an error; however, it does not call
yyerror
, and does not print any message. If you want to print an error message, callyyerror
explicitly before the ‘YYERROR;’ statement. See Error Recovery.
The expression
YYRECOVERING ()
yields 1 when the parser is recovering from a syntax error, and 0 otherwise. See Error Recovery.
Variable containing either the lookahead token, or
YYEOF
when the lookahead is the end of the input stream, orYYEMPTY
when no lookahead has been performed so the next token is not yet known. Do not modifyyychar
in a deferred semantic action (see GLR Semantic Actions). See Lookahead Tokens.
Discard the current lookahead token. This is useful primarily in error rules. Do not invoke
yyclearin
in a deferred semantic action (see GLR Semantic Actions). See Error Recovery.
Resume generating error messages immediately for subsequent syntax errors. This is useful primarily in error rules. See Error Recovery.
Variable containing the lookahead token location when
yychar
is not set toYYEMPTY
orYYEOF
. Do not modifyyylloc
in a deferred semantic action (see GLR Semantic Actions). See Actions and Locations.
Variable containing the lookahead token semantic value when
yychar
is not set toYYEMPTY
orYYEOF
. Do not modifyyylval
in a deferred semantic action (see GLR Semantic Actions). See Actions.
Acts like a structure variable containing information on the textual location of the grouping made by the current rule. See Tracking Locations.
Acts like a structure variable containing information on the textual location of the nth component of the current rule. See Tracking Locations.