+File: bison.info, Node: Locations Overview, Next: Bison Parser, Prev: Semantic Actions, Up: Concepts
+
+Locations
+=========
+
+ Many applications, like interpreters or compilers, have to produce
+verbose and useful error messages. To achieve this, one must be able to
+keep track of the "textual position", or "location", of each syntactic
+construct. Bison provides a mechanism for handling these locations.
+
+ Each token has a semantic value. In a similar fashion, each token
+has an associated location, but the type of locations is the same for
+all tokens and groupings. Moreover, the output parser is equipped with
+a default data structure for storing locations (*note Locations::, for
+more details).
+
+ Like semantic values, locations can be reached in actions using a
+dedicated set of constructs. In the example above, the location of the
+whole grouping is `@$', while the locations of the subexpressions are
+`@1' and `@3'.
+
+ When a rule is matched, a default action is used to compute the
+semantic value of its left hand side (*note Actions::). In the same
+way, another default action is used for locations. However, the action
+for locations is general enough for most cases, meaning there is
+usually no need to describe for each rule how `@$' should be formed.
+When building a new location for a given grouping, the default behavior
+of the output parser is to take the beginning of the first symbol, and
+the end of the last symbol.
+
+\1f
+File: bison.info, Node: Bison Parser, Next: Stages, Prev: Locations Overview, Up: Concepts
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