... I don't understand ... this line ...
(?(?{ $run[-1] - $run[-2] != 1 }) (*F))
Is that double-eval'ed or executed? What is the '*F'
referencing ...
The embedded code is executed.
+----------------------+------ embedded Perl code
| |
v v
(?(?{ $run[-1] - $run[-2] != 1 }) (*F))
This is the "(?(*condition*)*yes-pattern*)" regex expression
added with Perl version 5.10 (see Extended Patterns
in perlre).
In this case, the *condition*
is the true/false result of evaluating the code. If true, the
(*F) (a.k.a. (*FAIL))
backtracking
control verb is executed and the match fails and backtracks to the
most recent successfully matched substring:
a sequence with incrementing values for $3.
... what is the '$^N' ...
The $^N Perl special variable (see
Variables related to regular expressions
in perlvar) returns the value of the most recently closed
capture group.
Give a man a fish: <%-{-{-{-<
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