Evan Lavelle wrote:
Fernando Ferreira wrote:
The reason for my request is that, as bison generates LR parsers,
there is no way to, for instance, execute an action before a rule is
reduced, only after.
I've never tried an action at the start of a rule, but I'm pretty sure
that you can do it. Look up 'embedded actions' in the O'Reilly
lex&yacc book, or 3.5.5 'Actions in mid-rule' in the Bison 2.0 manual.
It may be difficult to avoid conflicts, though. According to the
O'Reilly book, yacc implements embedded actions using the technique
described at the end of 3.5.5 ("Another solution is to bury the action
inside a nonterminal symbol which serves as a subroutine...").
Evan
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But that would mean that I would have to add the same action for every
rule. My intention is to have a way to execute an single action before
any and every rule gets executed, similarly to YY_USER_ACTION on Flex.
An example would be to print the name of the rule that is about to be
reduced, using something like yy_reduce_print_ uses, "cout<<
yytname_[yyr2_[yyn]]". That's a silly example, there are other truly
marvelous uses for this feature which this margin is too narrow to
contain (hehe).
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