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Magic Words


posts: 1912

 


> FAhO is equivalent to
> "silence forever on this input stream". What's important is less its
> effect on following words (there are no following words; they don't
> count or are a different stream), but under what circumstances is its
> own functioning cancelled.

In left-to-right, it will be cancelled whenever there is a preceding
word that grabs it as "any-word". Those cases are: {zo fa'o},
{lo'u ... fa'o ...le'u}, {zoi fa'o .... fa'o}, and {da zei fa'o}.

Making {fa'o} not count as "any-word" in any one of those
would constitute an exception to left-to-right processing.

If {fa'o} does not allow reading any following words, then
{fa'o bu}, {fa'o zei da}, {fa'o si}, {fa'o sa ...}, {fa'o su}
are all impossible: {fa'o} is active here and there cannot be
any following words to parse.

{ba'e fa'o} is not problematic: an emphatic end-of-text.
{sa fa'o} is not problematic either: it will delete everything
because it won't find any other word from selmaho FAhO, and
then {fa'o} itself will end text. It has the same effect as
{su fa'o}.

> Since it does affect the whole input and
> parsing routine, this is more "magical" than working out when the
> function of LE or BAI is cancelled.

Yes, it's much more powerful once it can fulfill its function, but
that doesn't seem like a reason to introduce exceptions to allow it
to fulfill its function in places where no other word is allowed to.

There are other issues I have with FAhO, though.

1) If we really need such a metagrammatical word for
end-of-parsable-input, how come a corresponding word for
beginning-of-parsable-input is not needed?

2) At least in Robin's parser implementation, FAhO has a true
magic word grammatical function besides its end-of-parsable-input
metagrammatical function. If I understand correctly, in Robin's
parser FAhO swallows also any preceding word that makes the
text ungrammatical. So for example: {mi klama le zarci le fa'o}
will be parsed as {mi klama le zarci /ku/ /vau/ fa'o}. So FAhO
is also in the SI, SA, SU group in that it erases zero or more
preceding words.

3) I think it would be better if FAhO was just an "end of
grammatical text" (elidable) terminator, i.e.:
text = (rest of grammar) /FAhO/
This way it would not be a magic word, it could be erased
with SI/SA/SU, and used as "any-word" by BU and ZEI.
So you could easily fix a {fa'o si fo'a} mistake.

Recognizing end-of-parsable-input is a metagrammatical
function, akin to recognizing beginning-of-parsable-input.
Doing it with a word that can also be used within the
grammar (as in {zo fa'o}) is weird.

mu'o mi'e xorxes

 


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