Re: Insertions

On Tuesday 24 May 2022 16:36:46 (+02:00), C. M. Sperberg-McQueen wrote:

 >
 > Norm Tovey-Walsh writes:
 >
 > >> By the way, note that the following is now legal ixml:
 > >>
 > >> values: value+++",".
 >
 > > What does that mean?
 >
 > For what it's worth, I take it to mean
 >
 > <repeat1>
 >     <nonterminal name="value"/>
 >     <sep>
 >         <insertion string=","/>
 >     </
 > </
This is exactly right. An insertion matches zero characters on input, but 
produces characters on output. For instance:

    data: ~[]+++" ".

would insert a space between each character.

    abc => <data>a b c</data>

    values: [Nd]+++", ".

Would insert a comma and a space between each digit.

    123 => <values>1, 2, 3</values>

Steven

 > If it is, then there is no separator, and the grammar of which this
 > fragment is part will work best for values with fixed length or values
 > which somehow can be parsed without delimiters. If every value must
 > begin with a letter and end with a digit, then a1bc23def456 can be
 > uniquely parsed without delimiters, right?
 >
 > For things like integers or decimal numbers, this grammar would make
 > sense perhaps in a stress test checking how well the processor deals
 > with finite, but fast-growing, ambiguity. Given
 >
 > value = ['0'-'9']+.
 >
 > and the input '12345', I'll get one parse with five values, one parse
 > with one value, four each with two or four values, and seven with three
 > values. So seventeen overall.
 >
 > (Hmm. This is not Pascal's Triangle. But I'm sure there is a
 > formula for how many ways there are to partition a sequence of length n
 > into k contiguous subsequences. I just can't remember.)
 >
 >
 > Michael
 >
--

Received on Thursday, 26 May 2022 12:28:21 UTC