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* tests/glr-regression.at (Uninitialized location when reporting

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ambiguity): New test case.
* data/glr.c (yyresolveLocations): New function, which uses
YYLLOC_DEFAULT.
(yyresolveValue): Invoke yyresolveLocations before reporting an
ambiguity.
* doc/bison.texinfo (Default Action for Locations): Note
YYLLOC_DEFAULT's usage for ambiguity locations.
(GLR Semantic Actions): Cross-reference those notes.
This commit is contained in:
Joel E. Denny
2006-03-06 07:39:11 +00:00
parent ae952af227
commit 8710fc41aa
4 changed files with 156 additions and 4 deletions
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17
doc/bison.texinfo
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@@ -1135,13 +1135,16 @@ memory referenced by @code{yylval}.
@findex YYERROR
@cindex @acronym{GLR} parsers and @code{YYERROR}
Another Bison feature requiring special consideration is @code{YYERROR}
(@pxref{Action Features}), which you can invoke in any semantic action to
(@pxref{Action Features}), which you can invoke in a semantic action to
initiate error recovery.
During deterministic @acronym{GLR} operation, the effect of @code{YYERROR} is
the same as its effect in an @acronym{LALR}(1) parser.
In a deferred semantic action, its effect is undefined.
@c The effect is probably a syntax error at the split point.
Also, see @ref{Location Default Action, ,Default Action for Locations}, which
describes a special usage of @code{YYLLOC_DEFAULT} in @acronym{GLR} parsers.
@node Compiler Requirements
@subsection Considerations when Compiling @acronym{GLR} Parsers
@cindex @code{inline}
@@ -3571,6 +3574,7 @@ This location is stored in @code{yylloc}.
@node Location Default Action
@subsection Default Action for Locations
@vindex YYLLOC_DEFAULT
@cindex @acronym{GLR} parsers and @code{YYLLOC_DEFAULT}
Actually, actions are not the best place to compute locations. Since
locations are much more general than semantic values, there is room in
@@ -3578,6 +3582,9 @@ the output parser to redefine the default action to take for each
rule. The @code{YYLLOC_DEFAULT} macro is invoked each time a rule is
matched, before the associated action is run. It is also invoked
while processing a syntax error, to compute the error's location.
Before reporting an unresolvable syntactic ambiguity, a @acronym{GLR}
parser invokes @code{YYLLOC_DEFAULT} recursively to compute the location
of that ambiguity.
Most of the time, this macro is general enough to suppress location
dedicated code from semantic actions.
@@ -3586,9 +3593,11 @@ The @code{YYLLOC_DEFAULT} macro takes three parameters. The first one is
the location of the grouping (the result of the computation). When a
rule is matched, the second parameter identifies locations of
all right hand side elements of the rule being matched, and the third
parameter is the size of the rule's right hand side. When processing
a syntax error, the second parameter identifies locations of
the symbols that were discarded during error processing, and the third
parameter is the size of the rule's right hand side.
When a @acronym{GLR} parser reports an ambiguity, which of multiple candidate
right hand sides it passes to @code{YYLLOC_DEFAULT} is undefined.
When processing a syntax error, the second parameter identifies locations
of the symbols that were discarded during error processing, and the third
parameter is the number of discarded symbols.
By default, @code{YYLLOC_DEFAULT} is defined this way: