Node:How Precedence, Previous:Precedence Examples, Up:Precedence
The first effect of the precedence declarations is to assign precedence levels to the terminal symbols declared. The second effect is to assign precedence levels to certain rules: each rule gets its precedence from the last terminal symbol mentioned in the components. (You can also specify explicitly the precedence of a rule. See 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 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 precedence level. The
verbose output file made by -v (see Invoking Bison) says
how each conflict was 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.