Re: [bpfk] One cannot refer to inner nodes in Lojban PEG

2015-04-07 20:18 GMT+03:00 Alex Burka <durka42@gmail.com>:

I guess I don't follow. If string_1 doesn't want to have all of the possible string_3 realizations inside, then why does it ask for string_3? In this example, just use

string_1 = string_2 / string_6 string_8

instead. Can you make a more concrete example?

You can't do that because then you will lose string_3 level. That's what I was talking about in the thread about sumti always having a tag. Similar constructs like BAI term, FA term and bare term must always be at the same level of hierarchy. You shouldn't remove any parent nodes. Unfortunately this is what Lojban PEG currently is in some cases.

What specific "actions" differ depending on whether a term contains FA or BAI?

This is the hierarchy for BAI:

terms => terms_1 => terms_2 => abs_term => abs_term_1 => abs_tag_term => tag => tense_modal

For FA it must be the same but with FA instead of tense_modal.

For bare sumti it must be the same but with FA_elidible instead of tense_modal.

mu'o mi'e durkavore

On Tuesday, April 7, 2015 at 4:28 AM, Gleki Arxokuna wrote:

Consider the following:
string_1 = string_2 / string_6 string_3
string_3 = string_7 / string_8
string_4 = !string_1 string_5

Now we need !string_1 to work only if string_8 matches, not when string_7 matches.
Why we might need that? E.g. for terms that can have either FA or BAI inside. Depending on whether we have FA or BAI inside a term our actions may differ.

How can we implement that?
We can just create duplicates of two strings like this:

string_1 = string_2 / string_6 string_3
string_1_2 = string_2 / string_6 string_3_2
string_3 = string_7 / string_8
string_3_2 = string_8
string_4 = !string_1_2 string_5

Now string_1_2 is the same as string_1 but it is matched only if string_8 matches (unlike string_1, otherwise they are the same).

Now the question is how do we avoid such duplication?

The answer from peg.js developers:
<quote>
Sorry, but there is currently no clean way to avoid the duplication.

In the future I'm thinking about adding support for rule templates/parametrizable rules, which would help here:

string_1<T> = string_2 / string_6 T
string_3 = string_7 / string_8
string_3_2 = string_8
string_4 = !string_1<string_3_2> string_5

And I think it'd be nice
</quote>

So for now our only chance is to copy paster parts of Lojban PEG if we want such things. I.e. one would need to split terms into "terms_for_BAI", "terms_for_FA" etc. with all their inner variables copied.

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