Re: {{ double braces }}

[Taco Hoekwater <taco@elvenkind.com>]

Taco Hoekwater wrote:
> 
> with lpeg, the code looks a bit harder, but is still short and
> relatively shortforward:

Here is a smarter lpeg that takes care of embedded \{ as well:

   local P, S, V = lpeg.P, lpeg.S, lpeg.V
   local matchtable = {
      "TEXT",
      TEXT = (V("FOOTNOTE") + 1)^0 * -1,
      SP = S(" \n\t")^0,
      BODY = "{"*(P("\\{")+P("\\}")+(1 - S("{}"))+V("BODY"))^0*"}",
      FOOTNOTE = "\\footnote" * V("SP") * V("BODY") / print,
   }
   lpeg.match(matchtable, data)

Quick explanation:

the symbol + is alternation, * is concatenation, - is exclusion,
^ is a repeat modifier, "" and P("") match strings, numbers
match bytes, S("") matches byte sets.

the "matchtable" describes the input data. In there,
matchtable[1] points to the "top" rule, which is "TEXT".
The other key-value pairs in the table say roughly this:

TEXT = an optional sequence [^0] of either footnote items
        [V("FOOTNOTE")] or non-footnote bytes [1], until
        the end of the data is reached [-1]
FOOTNOTE = the string '\footnote', followed by optional
        space, followed by the footnote body.
SP = zero or more occurrences of a space, tab, or newline byte
BODY = a left brace, followed by an optional sequence of
        four possible things:
        1. the string "\{" [P("\\{")]
        2. the string "\}" [P("\\}")]
        3. a byte that is not "{" nor "}"  [(1 - S("{}"))]
        4. a recursively included braced body [V("BODY")],
        followed by a right brace.

The [/print] runs the print() command on each successful
FOOTNOTE match.

Best wishes,
Taco

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