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If you are using the ‘@n’-feature (see Tracking 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.