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(bison.info)Token Positions

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Textual Positions of Tokens
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   If you are using the `@N'-feature (*note Tracking Locations:
Locations.) in actions to keep track of the textual locations of tokens
and groupings, then you must provide this information in `yylex'.  The
function `yyparse' expects to find the textual location of a token just
parsed in the global variable `yylloc'.  So `yylex' must store the
proper data in that variable.

   By default, the value of `yylloc' is a structure and you need only
initialize the members that are going to be used by the actions.  The
four members are called `first_line', `first_column', `last_line' and
`last_column'.  Note that the use of this feature makes the parser
noticeably slower.

   The data type of `yylloc' has the name `YYLTYPE'.