Re: Second expression in sequence confusion FreeLink <- "[[" .{&[>\]]} "]]"

Hi Tim,

On Tue, 10 Sep 2019, gettimothy wrote:

> Hi Levente.
>
> If you don't have time for this, "No" is  a good answer.
>
> I have the WikiMedia freelinks working. https://en.wikipedia.org/wiki/Help:Wikitext#Free_links
>
> [[This Is A Link]] generates 
>
> <a href="https://en.wikipedia.org/wiki/This_is_a_link">This is a link</a>
>
> I would like to translate the FreeLink <- "[[" .{&[>\]]} "]]" sequence into something like
>
> FreeLink <- LinkOpen  .{&[>\]]}  LinkClose
> LinkOpen   <- BracketOpen BracketOpen
> LinkClose   <- BracketClose BracketClose
> BracketOpen <- "["
> BracketClose <- "]"
>
> so that I can iteratively build up to more complicated link styles.
>
> That Capture in the middle of the sequence is giving me fits.
> Something as simple as:
>
> FreeLink <- LinkOpen  .{&[>\]]}  LinkClose
>
> does not parse as neither LinkOpen nor LinkClose are consumed.
>
> My interpretation of that middle sequence term is:
> "." get the next character and consume it.
> {&[>\]]} apply expression &[>\]] and capture the string that matched it for later use.

In Xtreams-Parsing, braces don't mean capture. They mean cardinality. It
comes from common regular expression syntax.
The regular expression x{1,3} means x 1 to 3 times, so it accepts x,
xx, and xxx.
You can also pass a single number x{3}, which is a shorthand for xxx.
You can also omit the second argument like in x{3,}, which means x 3 or
more times.
This construct is extended in Xtreams-Parsing with a stop expression.
"x"{"y"} means, accept any number of x up until y comes. Consume y too,
but don't yield it. So, such expression accepts: xy, xxy, xxxy, xxxxy,
etc, and yields x, xx, xxx, xxxx, etc.

I suspect having & inside {} probably causes problems, because {} tries to
consume what it parses, but & tells the parser not to consume what comes
after it.

If I were to write the FreeLink rule, it would be something like:

FreeLink <- "[[" .{"]]"}

It means: take two opening braces, accept and yield everything up to two
closing braces, then consume those too, but don't yield them.


Levente

> &[>\]] AND predicate : indicate success if expression [>\]] matches text ahead; otherwise indicate failure. do not consume text.
> [>\]]  character range between ">" and "]"
>
>
> Thanks for your time.
>
> cordially,
>
> t
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