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(bison.info)Location Default Action

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Default Action for Locations
----------------------------

   Actually, actions are not the best place to compute locations. Since
locations are much more general than semantic values, there is room in
the output parser to redefine the default action to take for each rule.
The `YYLLOC_DEFAULT' macro is called each time a rule is matched,
before the associated action is run.

   Most of the time, this macro is general enough to suppress location
dedicated code from semantic actions.

   The `YYLLOC_DEFAULT' macro takes three parameters. The first one is
the location of the grouping (the result of the computation). The
second one is an array holding locations of all right hand side
elements of the rule being matched. The last one is the size of the
right hand side rule.

   By default, it is defined this way:

     #define YYLLOC_DEFAULT(Current, Rhs, N)         \
       Current.last_line   = Rhs[N].last_line;       \
       Current.last_column = Rhs[N].last_column;

   When defining `YYLLOC_DEFAULT', you should consider that:

   * All arguments are free of side-effects. However, only the first
     one (the result) should be modified by `YYLLOC_DEFAULT'.

   * Before `YYLLOC_DEFAULT' is executed, the output parser sets `@$'
     to `@1'.

   * For consistency with semantic actions, valid indexes for the
     location array range from 1 to N.