Next: , Previous: , Up: Bison Declarations   [Contents][Index]

3.7.3 Operator Precedence

Use the %left, %right, %nonassoc, or %precedence declaration to declare a token and specify its precedence and associativity, all at once. These are called precedence declarations. See Operator Precedence, for general information on operator precedence.

The syntax of a precedence declaration is nearly the same as that of %token: either

%left symbols


%left <type> symbols

And indeed any of these declarations serves the purposes of %token. But in addition, they specify the associativity and relative precedence for all the symbols:

For backward compatibility, there is a confusing difference between the argument lists of %token and precedence declarations. Only a %token can associate a literal string with a token kind name. A precedence declaration always interprets a literal string as a reference to a separate token. For example:

%left  OR "<="         // Does not declare an alias.
%left  OR 134 "<=" 135 // Declares 134 for OR and 135 for "<=".

Next: Nonterminal Symbols, Previous: Token Kind Names, Up: Bison Declarations   [Contents][Index]