Sorry, one more thing. :^)

Angel Faus and I were discussing the best way to handle multiple backtracking thingies in the same regexp without one backtracking thingie trying to use another's index. I suggested pushing a mark (a special value, probably -1) onto the stack; if rePopindex popped a mark, it will have 'failed', and thus it would jump to the address given as its parameter. That would work something like this: 

RE:
    #set up flags and stuff
    branch $start
$advance:
    rePopindex
    reAdvance $fail
$start:
    reLiteral "f", $advance
    rePushindex
    rePushmark
$findo:
    rePushindex
    reLiteral "o", $findbar
    branch $findo
$backo:
    rePopindex $advance
$findbar:
    reLiteral "o", $backo
    set I0, 1
    reFinished
$fail:
    set I0, 0
    reFinished

[download]
Angel suggested that when we push an address onto the stack, we give it a label as a parameter; if a matching operation fails, it pops an index/label pair off the stack, sets the index and jumps to the label. Something like this: 
RE:
    #set up flags and stuff
    reOnfail $fail  #if there's nothing left on the stack
    branch $start
$advance:
    reAdvance
$start:
    rePushindex $advance
    reLiteral "f"
$findo:
    rePushindex $findbar
    reLiteral "o"
    branch $findo
$findbar:
    reLiteral "bar"
    set I0, 1
    reFinished
$fail:
    set I0, 0
    reFinished

[download]
Can you give me any guidance about which will work better in the long run? Angel's idea has ease-of-code-generation and code compactness going for it; mine has explicitness (for debugging) and flexibility. From what I can tell, alternation will be a bitch with either, but mine should be easier; same with optional constructs and lookaheads, from what I can see. (Of course, I could just be blinded because one is my idea and the other is someone else's; that's why I'm asking you.)

Thank you for helping me out with this. Discussing it with an expert has made this a hundred times better than it was.

=cut
--Brent Dax
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In reply to Re: Re: Re: Re: Re: Re: Flattening REs into opcodes for Perl 6 by BrentDax
in thread Flattening REs into opcodes for Perl 6 by BrentDax

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