X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/a0de5091fc13a2fe53f72e6b2d3054b745d9dd8a..31984206a710101776d1db64009aff6c7962551c:/doc/bison.texinfo diff --git a/doc/bison.texinfo b/doc/bison.texinfo index 4b49c811..a706a96d 100644 --- a/doc/bison.texinfo +++ b/doc/bison.texinfo @@ -4851,6 +4851,48 @@ Some of the accepted @var{variable}s are: @item Default Value: @code{"pull"} @end itemize +@item lr.keep_unreachable_states +@findex %define lr.keep_unreachable_states + +@itemize @bullet +@item Language(s): all + +@item Purpose: Requests that Bison allow unreachable parser states to remain in +the parser tables. +Bison considers a state to be unreachable if there exists no sequence of +transitions from the start state to that state. +A state can become unreachable during conflict resolution if Bison disables a +shift action leading to it from a predecessor state. +Keeping unreachable states is sometimes useful for analysis purposes, but they +are useless in the generated parser. + +@item Accepted Values: Boolean + +@item Default Value: @code{"false"} + +@item Caveats: + +@itemize @bullet +@item Unreachable states may contain conflicts and may reduce rules not +reduced in any other state. +Thus, keeping unreachable states may induce warnings that are irrelevant to +your parser's behavior, and it may eliminate warnings that are relevant. +Of course, the change in warnings may actually be relevant to a parser table +analysis that wants to keep unreachable states, so this behavior will likely +remain in future Bison releases. + +@item While Bison is able to remove unreachable states, it is not guaranteed to +remove other kinds of useless states. +Specifically, when Bison disables reduce actions during conflict resolution, +some goto actions may become useless, and thus some additional states may +become useless. +If Bison were to compute which goto actions were useless and then disable those +actions, it could identify such states as unreachable and then remove those +states. +However, Bison does not compute which goto actions are useless. +@end itemize +@end itemize + @item namespace @findex %define namespace @@ -7387,7 +7429,7 @@ with some set of possible lookahead tokens. When run with @example state 8 - exp -> exp . '+' exp [$, '+', '-', '/'] (rule 1) + exp -> exp . '+' exp (rule 1) exp -> exp '+' exp . [$, '+', '-', '/'] (rule 1) exp -> exp . '-' exp (rule 2) exp -> exp . '*' exp (rule 3)