(1) while *::array* is ok for both lexemes and G1 rules, to let the user see both the parse result and and how it is parsed, I'd suggest the following defaults I've caught myself using frequently:
:default ::= action => [lhs,values] lexeme default = action => [lhs,value] forgiving => 1 where *lhs *should be the LHS's name which is not currently the case: lhs command returns LHS's id, so some change would be needed, like making *lhs* return LHS name and, perhaps, adding *lhs_id* command. (2) defaults, *per se*, are invoked when a user omits something; with that in mind I'd suggest checking if *:default* and *lexeme default* are in the user grammar and add the defaults if they aren't. This also allows the old code run unchanged. Finally, something I'm not sure about: a developer version with meta grammar converted to forgiving to let people test against it and see if and how exactly it is (in)compatible. Hope this helps, -- rns. On Sat, Feb 15, 2014 at 7:29 PM, Jeffrey Kegler < jeffreykeg...@jeffreykegler.com> wrote: > I'd like opinions on adding a "interface" statement to the SLIF. > Currently, for backward compatibility reasons, some of the defaults are > not the best. I'd like to add a > > interface 2 > > statement which, if present, will makes these the new defaults: > > lexeme default = forgiving => 1 > :default ::= action => ::array > > The first line would make LATM the default, and the second would make > the make the default semantics for rules return the child values in > an array. > > A specific reason for changing the default for rule semantics is that > in the first stages of development, array output is useful in checking > your grammar. So it's a great way to start. > > The current behavior, returning 'undef' by default, is especially > perplexing to newcomers to Marpa. It means that, by default, value() > returns \undef on success, and undef on failure. This behavior is > unintuitive, unhelpful and confusing. > > A specific question I have: Should one of the bless options also be the > default for rules? If so, what about lexemes? A reason not to bless > is clutter. A reason to bless is that it provides even more information > for grammar checking. > > As usual, these defaults will be able to be overriden, but they do make > a real difference in convenience, and to those just finding their way > in Marpa. Whichever is the choice, I'll change all the synopses in the > docs to include a > > revision 2 > > statement at the beginning, so that it becomes more or less like the > "use strict", etc. incantation at the beginning of Perl scripts. > > Please comment or ask questions -- jeffrey > > -- > You received this message because you are subscribed to the Google Groups > "marpa parser" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to marpa-parser+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "marpa parser" group. To unsubscribe from this group and stop receiving emails from it, send an email to marpa-parser+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
