preprocessor directives.
The @code{#define} directive defines the macro @code{YYSTYPE}, thus
-specifying the C data type for semantic values of both tokens and groupings
-(@pxref{Value Type, ,Data Types of Semantic Values}). The Bison parser will use whatever type
-@code{YYSTYPE} is defined as; if you don't define it, @code{int} is the
-default. Because we specify @code{double}, each token and each expression
-has an associated value, which is a floating point number.
+specifying the C data type for semantic values of both tokens and
+groupings (@pxref{Value Type, ,Data Types of Semantic Values}). The
+Bison parser will use whatever type @code{YYSTYPE} is defined as; if you
+don't define it, @code{int} is the default. Because we specify
+@code{double}, each token and each expression has an associated value,
+which is a floating point number.
The @code{#include} directive is used to declare the exponentiation
function @code{pow}.
macro whose definition is the appropriate number. In this example,
therefore, @code{NUM} becomes a macro for @code{yylex} to use.
-The semantic value of the token (if it has one) is stored into the global
-variable @code{yylval}, which is where the Bison parser will look for it.
-(The C data type of @code{yylval} is @code{YYSTYPE}, which was defined
-at the beginning of the grammar; @pxref{Rpcalc Decls, ,Declarations for @code{rpcalc}}.)
+The semantic value of the token (if it has one) is stored into the
+global variable @code{yylval}, which is where the Bison parser will look
+for it. (The C data type of @code{yylval} is @code{YYSTYPE}, which was
+defined at the beginning of the grammar; @pxref{Rpcalc Decls,
+,Declarations for @code{rpcalc}}.)
A token type code of zero is returned if the end-of-file is encountered.
(Bison recognizes any nonpositive value as indicating the end of the
In a simple program it may be sufficient to use the same data type for
the semantic values of all language constructs. This was true in the
-RPN and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish Notation Calculator}).
+RPN and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish
+Notation Calculator}).
Bison's default is to use type @code{int} for all semantic values. To
specify some other type, define @code{YYSTYPE} as a macro, like this:
@findex %expect
Bison normally warns if there are any conflicts in the grammar
-(@pxref{Shift/Reduce, ,Shift/Reduce Conflicts}), but most real grammars have harmless shift/reduce
-conflicts which are resolved in a predictable way and would be difficult to
-eliminate. It is desirable to suppress the warning about these conflicts
-unless the number of conflicts changes. You can do this with the
-@code{%expect} declaration.
+(@pxref{Shift/Reduce, ,Shift/Reduce Conflicts}), but most real grammars
+have harmless shift/reduce conflicts which are resolved in a predictable
+way and would be difficult to eliminate. It is desirable to suppress
+the warning about these conflicts unless the number of conflicts
+changes. You can do this with the @code{%expect} declaration.
The declaration looks like this:
%expect @var{n}
@end example
-Here @var{n} is a decimal integer. The declaration says there should be no
-warning if there are @var{n} shift/reduce conflicts and no reduce/reduce
-conflicts. The usual warning is given if there are either more or fewer
-conflicts, or if there are any reduce/reduce conflicts.
+Here @var{n} is a decimal integer. The declaration says there should be
+no warning if there are @var{n} shift/reduce conflicts and no
+reduce/reduce conflicts. An error, instead of the usual warning, is
+given if there are either more or fewer conflicts, or if there are any
+reduce/reduce conflicts.
In general, using @code{%expect} involves these steps:
projects / bison.git / blobdiff