Would this work? I don't have the ops integrated into Parrot's normal set yet, but I'd like to know if I'm on the right track. re_match is like calling RE_0 as a subroutine, and re_finished is like returning from it. The set is an assignment (in this case to Integer register 0); pretty much everything else that may look odd in here has been explained inline. 
    re_match RE_0, "afoobarz"

RE_0:
    # /fo*?bar/s (and yes, the "s" flag is pointless)
    re_flags "s"
    re_minlength 4


$start:    #a 'local' label--it disappears the next time a normal
           # label is seen
    re_pushindex   #in case we fail in $find_o or something
    re_literal "f", $find_bar
    re_popindex
    re_advance $failure
    branch $start    #think "goto"
    
$find_o:
    re_literal "o", $find_bar
    branch $start

$find_bar:
    re_literal "bar", $success
    branch $find_o

$success:
    set I0, 1
    branch $end
$failure:
    set I0, 0
$end:
    re_finished

[download]
Looking at this, it seems that most of the time we use the second parameter we're trying to avoid a branch put in in case we fail; is this just a quirk of this example, or might it make more sense for the second parameter to represent where to jump if we fail? 
$start:
    re_pushindex
    re_literal "f", $advance

$find_bar:
    re_literal "bar", $find_o

    #if we made it this far, we're done!
    set I0, 1
    branch $end
    
$find_o:
    re_literal "o", $advance
    branch $find_bar

$advance:
    re_popindex
    re_advance $failure
    branch $start

$failure:
    set I0, 0

$end:
    re_finished

[download]
This would be a bigger win in the case of, say, several character classes in a row: 
RE_1:
    #/[az][by][cx]/
    re_flags ""
    re_minlength 3

$start:
    re_pushindex
    re_oneof "az", $advance
    re_oneof "by", $advance
    re_oneof "cx", $advance

    set I0, 1
    branch $end

$advance:
    re_popindex
    re_advance $fail
    branch $start

$fail:
    set I0, 0

$end:
    re_finished

[download]

=cut
--Brent Dax
There is no sig.

In reply to 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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