File Coverage

blib/lib/Regexp/Grammars.pm

Criterion	Covered	Total	%
statement	499	772	64.6
branch	265	454	58.3
condition	81	154	52.6
subroutine	49	69	71.0
pod	0	3	0.0
total	894	1452	61.5

=encoding ISO8859-1
=cut

package Regexp::Grammars;
use re 'eval';

use warnings;
use strict;
use 5.010;
use vars ();

use Scalar::Util qw< blessed reftype >;
use Data::Dumper qw< Dumper  >;

our $VERSION = '1.056';

my $anon_scalar_ref = \do{my $var};
my $MAGIC_VARS = q{my ($CAPTURE, $CONTEXT, $DEBUG, $INDEX, $MATCH, %ARG, %MATCH);};

my $PROBLEM_WITH_5_18 = <<'END_ERROR_MSG';
Warning: Regexp::Grammars is unsupported
         under Perl 5.18.0 through 5.18.3 due to a bug
         in regex parsing under those versions.

         Please upgrade to Perl 5.18.4 or later, or revert to
         Perl 5.16 or earlier.
END_ERROR_MSG

# Load the module...
sub import {
    # Signal lexical scoping (active, unless something was exported)...
    $^H{'Regexp::Grammars::active'} = 1;

    # Process any regexes in module's active lexical scope...
    use overload;
    overload::constant(
        qr => sub {
            my ($raw, $cooked, $type) = @_;
            # In active scope and really a regex...
            if (_module_is_active() && $type =~ /qq?/) {
                return bless \$cooked, 'Regexp::Grammars::Precursor';
            }
            # Ignore everything else...
            else {
                return $cooked;
            }
        }
    );

    # Deal with 5.18 issues...
    if ($] >= 5.018) {
        # Issue warning...
        if ($] < 5.018004) {
            require Carp;
            Carp::croak($PROBLEM_WITH_5_18);
        }

        # Deal with cases where Perl 5.18+ complains about
        # the injection of (??{...}) and (?{...})
        require re;
        re->import('eval');

        # Sanctify the standard Regexp::Grammars pseudo-variables from
        # Perl 5.18's early enforcement of strictures...
        my $caller = caller;
        warnings->unimport('once');
        @_ = ( 'vars', '$CAPTURE', '$CONTEXT', '$DEBUG', '$INDEX', '$MATCH', '%ARG', '%MATCH' );
        goto &vars::import;
    }
}

# Deactivate module's regex effect when it is "anti-imported" with 'no'...
sub unimport {
    # Signal lexical (non-)scoping...
    $^H{'Regexp::Grammars::active'} = 0;
    require re;
    re->unimport('eval');
}

# Encapsulate the hoopy user-defined pragma interface...
sub _module_is_active {
    return (caller 1)[10]->{'Regexp::Grammars::active'};
}

my $RULE_HANDLER;
sub clear_rule_handler { undef $RULE_HANDLER; }

sub Regexp::with_actions {
    my ($self, $handler) = @_;
    $RULE_HANDLER = $handler;
    return $self;
}

#=====[ COMPILE-TIME INTERIM REPRESENTATION OF GRAMMARS ]===================
{
    package Regexp::Grammars::Precursor;

    # Only translate precursors once...
    state %grammar_cache;

    use overload (
        # Concatenation/interpolation just concatenates to the precursor...
        q{.} => sub {
            my ($x, $y, $reversed) = @_;
            if (ref $x) { $x = ${$x} }
            if (ref $y) { $y = ${$y} }
            if ($reversed) { ($y,$x) = ($x,$y); }
            $x .= $y//q{};
            return bless \$x, 'Regexp::Grammars::Precursor';
        },

        # Using as a string (i.e. matching) preprocesses the precursor...
        q{""} => sub {
            my ($obj) = @_;
            return $grammar_cache{ overload::StrVal($$obj) }
                //= Regexp::Grammars::_build_grammar( ${$obj} );
        },

        # Everything else, as usual...
        fallback => 1,
    );
}


#=====[ SUPPORT FOR THE INTEGRATED DEBUGGER ]=========================

# All messages go to STDERR by default...
*Regexp::Grammars::LOGFILE = *STDERR{IO};

# Debugging levels indicate where to stop...
our %DEBUG_LEVEL = (
    same => undef,                           # No change in debugging mode
    off  => 0,                               # No more debugging
    run  => 1,   continue  => 1,             # Run to completion of regex match
                 match     => 2,   on => 2,  # Run to next successful submatch
    step => 3,   try       => 3,             # Run to next reportable event
);

# Debugging levels can be abbreviated to one character during interactions...
@DEBUG_LEVEL{ map {substr($_,0,1)} keys %DEBUG_LEVEL } = values %DEBUG_LEVEL;
$DEBUG_LEVEL{o} = $DEBUG_LEVEL{off};      # Not "on"
$DEBUG_LEVEL{s} = $DEBUG_LEVEL{step};     # Not "same"

# Width of leading context field in debugging messages is constrained...
my $MAX_CONTEXT_WIDTH = 20;
my $MIN_CONTEXT_WIDTH = 6;

sub set_context_width {
    { package Regexp::Grammars::ContextRestorer;
      sub new {
        my ($class, $old_context_width) = @_;
        bless \$old_context_width, $class;
      }
      sub DESTROY {
        my ($old_context_width_ref) = @_;
        $MAX_CONTEXT_WIDTH = ${$old_context_width_ref};
      }
    }

    my ($new_context_width) = @_;
    my $old_context_width = $MAX_CONTEXT_WIDTH;
    $MAX_CONTEXT_WIDTH = $new_context_width;
    if (defined wantarray) {
        return Regexp::Grammars::ContextRestorer->new($old_context_width);
    }
}

# Rewrite a string currently being matched, to make \n and \t visible
sub _show_metas {
    my $context_str = shift // q{};

    # Quote newlines (\n -> \\n, without using a regex)...
    my $index = index($context_str,"\n");
    while ($index >= 0) {
        substr($context_str, $index, 1, '\\n');
        $index = index($context_str,"\n",$index+2);
    }

    # Quote tabs (\t -> \\t, without using a regex)...
    $index = index($context_str,"\t");
    while ($index >= 0) {
        substr($context_str, $index, 1, '\\t');
        $index = index($context_str,"\t",$index+2);
    }

    return $context_str;
}

# Minimize whitespace in a string...
sub _squeeze_ws {
    my ($str) = @_;

    $str =~ tr/\n\t/ /;

    my $index = index($str,q{  });
    while ($index >= 0) {
        substr($str, $index, 2, q{ });
        $index = index($str,q{  },$index);
    }

    return $str;
}

# Prepare for debugging...
sub _init_try_stack {
    our (@try_stack, $last_try_pos, $last_context_str);

    # Start with a representation of the entire grammar match...
    @try_stack = ({
        subrule => '',
        height  => 0,
        errmsg  => ' \\FAIL ',
    });

    # Initialize tracking of location and context...
    $last_try_pos     = -1;
    $last_context_str = q{};

    # Report...
    say {*Regexp::Grammars::LOGFILE} _debug_context('=>')
                . 'Trying  from position ' . pos();
}

# Create a "context string" showing where the regex is currently matching...
sub _debug_context {
    my ($fill_chars) = @_;

    # Determine minimal sufficient width for context field...
    my $field_width = length(_show_metas($_//q{}));
    if ($field_width > $MAX_CONTEXT_WIDTH) {
        $field_width = $MAX_CONTEXT_WIDTH;
    }
    elsif ($field_width < $MIN_CONTEXT_WIDTH) {
        $field_width = $MIN_CONTEXT_WIDTH;
    }

    # Get current matching position (and some additional trailing context)...
    my $context_str
        = substr(_show_metas(substr(($_//q{}).q{},pos()//0,$field_width)),0,$field_width);

    # Build the context string, handling special cases...
    our $last_context_str //= q{};
    if ($fill_chars) {
        # If caller supplied a 1- or 2-char fill sequence, use that instead...
        my $last_fill_char = length($fill_chars) > 1
                                ? substr($fill_chars,-1,1,q{})
                                : $fill_chars
                                ;
        $context_str = $fill_chars x ($field_width-1) . $last_fill_char;
    }
    else {
        # Make end-of-string visible in empty context string...
        if ($context_str eq q{}) {
            $context_str = '[eos]';
        }

        # Don't repeat consecutive identical context strings...
        if ($context_str eq $last_context_str) {
            $context_str = q{ } x $field_width;
        }
        else {
            # If not repeating, remember for next time...
            $last_context_str = $context_str;
        }
    }

    # Left justify and return context string...
    return sprintf("%-*s ",$field_width,$context_str);
}

# Show a debugging message (mainly used for compile-time errors and info)...
sub _debug_notify {
    # Single arg is a line to be printed with a null severity...
    my ($severity, @lines) = @_==1 ? (q{},@_) : @_;
    chomp @lines;

    # Formatting string for all lines...
    my $format = qq{%*s | %s\n};

    # Track previous severity and avoid repeating the same level...
    state $prev_severity = q{};
    if ($severity !~ /\S/) {
        # Do nothing
    }
    elsif ($severity eq 'info' && $prev_severity eq 'info' ) {
        $severity = q{};
    }
    else {
        $prev_severity = $severity;
    }

    # Display first line with severity indicator (unless same as previous)...
    printf {*Regexp::Grammars::LOGFILE} $format, $MIN_CONTEXT_WIDTH, $severity, shift @lines;

    # Display first line without severity indicator
    for my $next_line (@lines) {
        printf {*Regexp::Grammars::LOGFILE} $format, $MIN_CONTEXT_WIDTH, q{}, $next_line;
    }
}

# Handle user interactions during runtime debugging...
sub _debug_interact {
    my ($stack_height, $leader, $curr_frame_ref, $min_debug_level) = @_;

    our $DEBUG; # ...stores current debug level within regex

    # Only interact with terminals, and if debug level is appropriate...
    if (-t *Regexp::Grammars::LOGFILE
    &&  defined $DEBUG
    &&  ($DEBUG_LEVEL{$DEBUG}//0) >= $DEBUG_LEVEL{$min_debug_level}
    ) {
        local $/ = "\n";  # ...in case some caller is being clever
        INPUT:
        while (1) {
            my $cmd = readline // q{};
            chomp $cmd;

            # Input of 'd' means 'display current result frame'...
            if ($cmd eq 'd') {
                print {*Regexp::Grammars::LOGFILE} join "\n",
                    map { $leader . ($stack_height?'|   ':q{})
                        . '       : ' . $_
                        }
                        split "\n", q{ }x8 . substr(Dumper($curr_frame_ref),8);
                print "\t";
            }
            # Any other (valid) input changes debugging level and continues...
            else {
                if (defined $DEBUG_LEVEL{$cmd}) { $DEBUG = $cmd; }
                last INPUT;
            }
        }
    }
    # When interaction not indicated, just complete the debugging line...
    else {
        print {*Regexp::Grammars::LOGFILE} "\n";
    }
}

# Handle reporting of unsuccessful match attempts...
sub _debug_handle_failures {
    my ($stack_height, $subrule, $in_match) = @_;
    our @try_stack;

    # Unsuccessful match attempts leave "leftovers" on the attempt stack...
    CLEANUP:
    while (@try_stack && $try_stack[-1]{height} >= $stack_height) {
        # Grab record of (potentially) unsuccessful attempt...
        my $error_ref = pop @try_stack;

        # If attempt was the one whose match is being reported, go and report...
        last CLEANUP if $in_match
                     && $error_ref->{height} == $stack_height
                     && $error_ref->{subrule} eq $subrule;

        # Otherwise, report the match failure...
        say {*Regexp::Grammars::LOGFILE} _debug_context(q{ }) . $error_ref->{errmsg};
    }
}

# Handle attempts to call non-existent subrules...
sub _debug_fatal {
    my ($naughty_construct) = @_;

    print {*Regexp::Grammars::LOGFILE}
        "_________________________________________________________________\n",
        "Fatal error: Entire parse terminated prematurely while attempting\n",
        "             to call non-existent rule: $naughty_construct\n",
        "_________________________________________________________________\n";
    $@ = "Entire parse terminated prematurely while attempting to call non-existent rule: $naughty_construct";
}

# Handle objrules that don't return hashes...
sub _debug_non_hash {
    my ($obj, $name) = @_;

    # If the object is okay, no further action required...
    return q{} if reftype($obj) eq 'HASH';

    # Generate error messages...
    print {*Regexp::Grammars::LOGFILE}
    "_________________________________________________________________\n",
    "Fatal error:  returned a non-hash-based object\n",
    "_________________________________________________________________\n";
    $@ = " returned a non-hash-based object";

    return '(*COMMIT)(*FAIL)';
}


# Print a  message in context...
sub _debug_logmsg {
    my ($stack_height, @msg) = @_;

    # Determine indent for messages...
    my $leader = _debug_context() . q{|   } x ($stack_height-1) . '|';

    # Report the attempt...
    print {*Regexp::Grammars::LOGFILE} map { "$leader$_\n" } @msg;
}

# Print a message indicating a (sub)match attempt...
sub _debug_trying {
    my ($stack_height, $curr_frame_ref, $subrule) = @_;

    # Clean up after any preceding unsuccessful attempts...
    _debug_handle_failures($stack_height, $subrule);

    # Determine indent for messages...
    my $leader = _debug_context() . q{|   } x ($stack_height-2);

    # Detect and report any backtracking prior to this attempt...
    our $last_try_pos //= 0;  #...Stores the pos() of the most recent match attempt?
    my $backtrack_distance = $last_try_pos - pos();
    if ($backtrack_distance > 0) {
        say {*Regexp::Grammars::LOGFILE} ' <' . q{~} x (length(_debug_context(q{ }))-3) . q{ }
                    . q{|   } x ($stack_height-2)
                    . qq{|...Backtracking $backtrack_distance char}
                    . ($backtrack_distance > 1 ? q{s} : q{})
                    . q{ and trying new match}
                    ;
    }

    # Report the attempt...
    print {*Regexp::Grammars::LOGFILE} $leader, "|...Trying $subrule\t";

    # Handle user interactions during debugging...
    _debug_interact($stack_height, $leader, $curr_frame_ref, 'step');

    # Record the attempt, for later error handling in _debug_matched()...
    if ($subrule ne 'next alternative') {
        our @try_stack;
        push @try_stack, {
            height  => $stack_height,
            subrule => $subrule,
            # errmsg should align under:              |...Trying $subrule\t
            errmsg  => q{|   } x ($stack_height-2) . "|    \\FAIL $subrule",
        };
    }
    $last_try_pos = pos();
}

# Print a message indicating a successful (sub)match...
sub _debug_matched {
    my ($stack_height, $curr_frame_ref, $subrule, $matched_text) = @_;

    # Clean up any intervening unsuccessful attempts...
    _debug_handle_failures($stack_height, $subrule, 'in match');

    # Build debugging message...
    my $debug_context = _debug_context();
    my $leader  = $debug_context . q{|   } x ($stack_height-2);
    my $message = ($stack_height ? '|   ' : q{})
                . " \\_____$subrule matched ";
    my $filler  = $stack_height
                    ? '|   ' . q{ } x (length($message)-4)
                    :          q{ } x  length($message);

    our $last_try_pos //= 0;  #...Stores the pos() of the most recent match attempt?

    # Report if match required backtracking...
    my $backtrack_distance = $last_try_pos - (pos()//0);
    if ($backtrack_distance > 0) {
        say {*Regexp::Grammars::LOGFILE} ' <' . q{~} x (length(_debug_context(q{ }))-3) . q{ }
                    . q{|   } x ($stack_height-2)
                    . qq{|...Backtracking $backtrack_distance char}
                    . ($backtrack_distance > 1 ? q{s} : q{})
                    . qq{ and rematching $subrule}
                    ;
    }
    $last_try_pos = pos();

    # Format match text (splitting multi-line texts and indent them correctly)...
    $matched_text =  defined($matched_text)
        ? $matched_text = q{'} . join("\n$leader$filler", split "\n", $matched_text) . q{'}
        : q{};

    # Print match message...
    print {*Regexp::Grammars::LOGFILE} $leader . $message . $matched_text . qq{\t};

    # Check for user interaction...
    _debug_interact($stack_height, $leader, $curr_frame_ref, $stack_height ?  'match' : 'run');
}

# Print a message indicating a successful (sub)match...
sub _debug_require {
    my ($stack_height, $condition, $succeeded) = @_;

    # Build debugging message...
    my $debug_context = _debug_context();
    my $leader  = $debug_context . q{|   } x ($stack_height-1);
    my $message1 = ($stack_height ? '|...' : q{})
                 . "Testing condition: $condition"
                 ;
    my $message2 = ($stack_height ? '|   ' : q{})
                 . " \\_____"
                 . ($succeeded ? 'Satisfied' : 'FAILED')
                 ;

    # Report if match required backtracking...
    our $last_try_pos;
    my $backtrack_distance = $last_try_pos - pos();
    if ($backtrack_distance > 0) {
        say {*Regexp::Grammars::LOGFILE} ' <' . q{~} x (length(_debug_context(q{ }))-3) . q{ }
                    . q{|   } x ($stack_height-1)
                    . qq{|...Backtracking $backtrack_distance char}
                    . ($backtrack_distance > 1 ? q{s} : q{})
                    . qq{ and rematching}
                    ;
    }

    # Remember where the condition was tried...
    $last_try_pos = pos();

    # Print match message...
    say {*Regexp::Grammars::LOGFILE} $leader . $message1;
    say {*Regexp::Grammars::LOGFILE} $leader . $message2;
}

# Print a message indicating a successful store-result-of-code-block...
sub _debug_executed {
    my ($stack_height, $curr_frame_ref, $subrule, $value) = @_;

    # Build message...
    my $leader   = _debug_context() . q{|   } x ($stack_height-2);
    my $message  = "|...Action $subrule\n";
    my $message2 = "|   saved value: '";
    $message    .= $leader . $message2;
    my $filler   = q{ } x length($message2);

    # Split multiline results over multiple lines (properly indented)...
    $value = join "\n$leader$filler", split "\n", $value;

    # Report the action...
    print {*Regexp::Grammars::LOGFILE} $leader . $message . $value . qq{'\t};

    # Check for user interaction...
    _debug_interact($stack_height, $leader, $curr_frame_ref, 'match');
}

# Create the code to be inserted into the regex to facilitate debugging...
sub _build_debugging_statements {
    my ($debugging_active, $subrule, $extra_pre_indent) = @_;

    return (q{}, q{}) if ! $debugging_active;;

    $extra_pre_indent //= 0;

    $subrule = "q{$subrule}";

    return (
      qq{ Regexp::Grammars::_debug_trying(\@Regexp::Grammars::RESULT_STACK+$extra_pre_indent, \$Regexp::Grammars::RESULT_STACK[-2+$extra_pre_indent], $subrule)
            if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG};
        },
      qq{ Regexp::Grammars::_debug_matched(\@Regexp::Grammars::RESULT_STACK+1, \$Regexp::Grammars::RESULT_STACK[-1], $subrule, \$^N)
            if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG};
        },
    );
}

sub _build_raw_debugging_statements {
    my ($debugging_active, $subpattern, $extra_pre_indent) = @_;

    return (q{}, q{}) if ! $debugging_active;

    $extra_pre_indent //= 0;

    if ($subpattern eq '|') {
        return (
        q{},
        qq{
            (?{;Regexp::Grammars::_debug_trying(\@Regexp::Grammars::RESULT_STACK+$extra_pre_indent,
              \$Regexp::Grammars::RESULT_STACK[-2+$extra_pre_indent], 'next alternative')
                if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG};})
            },
        );
    }
    else {
        return (
        qq{
            (?{;Regexp::Grammars::_debug_trying(\@Regexp::Grammars::RESULT_STACK+$extra_pre_indent,
              \$Regexp::Grammars::RESULT_STACK[-2+$extra_pre_indent], q{subpattern /$subpattern/}, \$^N)
                if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG};})
            },
        qq{
            (?{;Regexp::Grammars::_debug_matched(\@Regexp::Grammars::RESULT_STACK+1,
              \$Regexp::Grammars::RESULT_STACK[-1], q{subpattern /$subpattern/}, \$^N)
                if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG};})
            },
        );
    }
}


#=====[ SUPPORT FOR AUTOMATIC TIMEOUTS ]=========================

sub _test_timeout {
    our ($DEBUG, $TIMEOUT);

    return q{} if time() < $TIMEOUT->{'limit'};

    my $duration = "$TIMEOUT->{duration} second"
                 . ( $TIMEOUT->{duration} == 1 ? q{} : q{s} );

    if (defined($DEBUG) && $DEBUG ne 'off') {
        my $leader   = _debug_context(q{ });
        say {*LOGFILE} $leader . '|';
        say {*LOGFILE} $leader . "|...Invoking {duration}>";
        say {*LOGFILE} $leader . "|   \\_____No match after $duration";
        say {*LOGFILE} $leader . '|';
        say {*LOGFILE} $leader . " \\FAIL ";
    }

    if (! @!) {
        @! = "Internal error: Timed out after $duration (as requested)";
    }
    return q{(*COMMIT)(*FAIL)};
}


#=====[ SUPPORT FOR UPDATING THE RESULT STACK ]=========================

# Create a clone of the current result frame with an new key/value...
sub _extend_current_result_frame_with_scalar {
    my ($stack_ref, $key, $value) = @_;

    # Autovivify null stacks (only occur when grammar invokes no subrules)...
    if (!@{$stack_ref}) {
        $stack_ref = [{}];
    }

    # Copy existing frame, appending new value so it overwrites any old value...
    my $cloned_result_frame = {
        %{$stack_ref->[-1]},
        $key => $value,
    };

    # Make the copy into an object, if the original was one...
    if (my $class = blessed($stack_ref->[-1])) {
        bless $cloned_result_frame, $class;
    }

    return $cloned_result_frame;
}

# Create a clone of the current result frame with an additional key/value
# (As above, but preserving the "listiness" of the key being added to)...
sub _extend_current_result_frame_with_list {
    my ($stack_ref, $key, $value) = @_;

    # Copy existing frame, appending new value to appropriate element's list...
    my $cloned_result_frame = {
        %{$stack_ref->[-1]},
        $key => [
            @{$stack_ref->[-1]{$key}//[]},
            $value,
        ],
    };

    # Make the copy into an object, if the original was one...
    if (my $class = blessed($stack_ref->[-1])) {
        bless $cloned_result_frame, $class;
    }

    return $cloned_result_frame;
}

# Pop current result frame and add it to a clone of previous result frame
# (flattening it if possible, and preserving any blessing)...
sub _pop_current_result_frame {
    my ($stack_ref, $key, $original_name, $value) = @_;

    # Where are we in the stack?
    my $curr_frame   = $stack_ref->[-1];
    my $caller_frame = $stack_ref->[-2];

    # Track which frames are objects...
    my $is_blessed_curr   = blessed($curr_frame);
    my $is_blessed_caller = blessed($caller_frame);

    # Remove "private" captures (i.e. those starting with _)...
    delete @{$curr_frame}{grep {substr($_,0,1) eq '_'} keys %{$curr_frame} };

    # Remove "nocontext" marker...
    my $nocontext = delete $curr_frame->{'~'};

    # Build a clone of the current frame...
    my $cloned_result_frame
        = exists $curr_frame->{'='}                                  ? $curr_frame->{'='}
        : $is_blessed_curr || length(join(q{}, keys %{$curr_frame})) ? { q{} => $value, %{$curr_frame} }
        : keys %{$curr_frame}                                        ? $curr_frame->{q{}}
        :                                                              $value
        ;

    # Apply any appropriate handler...
    if ($RULE_HANDLER) {
        if ($RULE_HANDLER->can($original_name) || $RULE_HANDLER->can('AUTOLOAD')) {
            my $replacement_result_frame
                = $RULE_HANDLER->$original_name($cloned_result_frame);
            if (defined $replacement_result_frame) {
                $cloned_result_frame = $replacement_result_frame;
            }
        }
    }

    # Remove capture if not requested...
    if ($nocontext && ref $cloned_result_frame eq 'HASH' && keys %{$cloned_result_frame} > 1) {
        delete $cloned_result_frame->{q{}};
    }

    # Nest a clone of current frame inside a clone of the caller frame...
    my $cloned_caller_frame = {
        %{$caller_frame//{}},
        $key => $cloned_result_frame,
    };

    # Make the copies into objects, if the originals were...
    if ($is_blessed_curr && !exists $curr_frame->{'='} ) {
        bless $cloned_caller_frame->{$key}, $is_blessed_curr;
    }
    if ($is_blessed_caller) {
        bless $cloned_caller_frame, $is_blessed_caller;
    }

    return $cloned_caller_frame;
}

# Pop current result frame and add it to a clone of previous result frame
# (flattening it if possible, and preserving any blessing)
# (As above, but preserving listiness of key being added to)...
sub _pop_current_result_frame_with_list {
    my ($stack_ref, $key, $original_name, $value) = @_;

    # Where are we in the stack?
    my $curr_frame   = $stack_ref->[-1];
    my $caller_frame = $stack_ref->[-2];

    # Track which frames are objects...
    my $is_blessed_curr = blessed($curr_frame);
    my $is_blessed_caller = blessed($caller_frame);

    # Remove "private" captures (i.e. those starting with _)...
    delete @{$curr_frame}{grep {substr($_,0,1) eq '_'} keys %{$curr_frame} };

    # Remove "nocontext" marker...
    my $nocontext = delete $curr_frame->{'~'};

    # Clone the current frame...
    my $cloned_result_frame
        = exists $curr_frame->{'='}                                  ? $curr_frame->{'='}
        : $is_blessed_curr || length(join(q{}, keys %{$curr_frame})) ? { q{} => $value, %{$curr_frame} }
        : keys %{$curr_frame}                                        ? $curr_frame->{q{}}
        :                                                              $value
        ;

    # Apply any appropriate handler...
    if ($RULE_HANDLER) {
        if ($RULE_HANDLER->can($original_name) || $RULE_HANDLER->can('AUTOLOAD')) {
            my $replacement_result_frame
                = $RULE_HANDLER->$original_name($cloned_result_frame);
            if (defined $replacement_result_frame) {
                $cloned_result_frame = $replacement_result_frame;
            }
        }
    }

    # Remove capture if not requested...
    if ($nocontext && ref $cloned_result_frame eq 'HASH' && keys %{$cloned_result_frame} > 1) {
        delete $cloned_result_frame->{q{}};
    }

    # Append a clone of current frame inside a clone of the caller frame...
    my $cloned_caller_frame = {
            %{$caller_frame},
            $key => [
                @{$caller_frame->{$key}//[]},
                $cloned_result_frame,
            ],
        };

    # Make the copies into objects, if the originals were...
    if ($is_blessed_curr && !exists $curr_frame->{'='} ) {
        bless $cloned_caller_frame->{$key}[-1], $is_blessed_curr;
    }
    if ($is_blessed_caller) {
        bless $cloned_caller_frame, $is_blessed_caller;
    }

    return $cloned_caller_frame;
}


#=====[ MISCELLANEOUS CONSTANTS ]=========================

# Namespace in which grammar inheritance occurs...
my $CACHE = 'Regexp::Grammars::_CACHE_::';
my $CACHE_LEN = length $CACHE;
my %CACHE; #...for subrule tracking

# This code inserted at the start of every grammar regex
#    (initializes the result stack cleanly and backtrackably, via local)...
my $PROLOGUE = q{((?{; @! = () if !pos;
                       local @Regexp::Grammars::RESULT_STACK
                           = (@Regexp::Grammars::RESULT_STACK, {});
                       local $Regexp::Grammars::TIMEOUT = { limit => -1>>1 };
                       local $Regexp::Grammars::DEBUG = 'off' }) };

# This code inserted at the end of every grammar regex
#    (puts final result in %/. Also defines default , , etc.)...
my $EPILOGUE = q{)(?{; $Regexp::Grammars::RESULT_STACK[-1]{q{}} //= $^N;;
         local $Regexp::Grammars::match_frame = pop @Regexp::Grammars::RESULT_STACK;
         delete @{$Regexp::Grammars::match_frame}{
                    '~', grep {substr($_,0,1) eq '_'} keys %{$Regexp::Grammars::match_frame}
                };
         if (exists $Regexp::Grammars::match_frame->{'='}) {
            if (ref($Regexp::Grammars::match_frame->{'='}) eq 'HASH') {
                $Regexp::Grammars::match_frame
                    = $Regexp::Grammars::match_frame->{'='};
            }
         }
         if (@Regexp::Grammars::RESULT_STACK) {
            $Regexp::Grammars::RESULT_STACK[-1]{'(?R)'}
                = $Regexp::Grammars::match_frame;
         }
         Regexp::Grammars::clear_rule_handler();
         */ = $Regexp::Grammars::match_frame;
    })|\Z(?{Regexp::Grammars::clear_rule_handler();})(?!)(?(DEFINE)
        (? \\s* )
        (?
                (?{$Regexp::Grammars::RESULT_STACK[-1]{'!'}=$#{!};})
                \\s*
                (?{;$#{!}=delete($Regexp::Grammars::RESULT_STACK[-1]{'!'})//0;
                           delete($Regexp::Grammars::RESULT_STACK[-1]{'@'});
                })
        )
        (? \\S+ )
        (?
                (?{$Regexp::Grammars::RESULT_STACK[-1]{'!'}=$#{!};})
                \\S+
                (?{;$#{!}=delete($Regexp::Grammars::RESULT_STACK[-1]{'!'})//0;
                           delete($Regexp::Grammars::RESULT_STACK[-1]{'@'});
                })
        )
        (? (?{; $Regexp::Grammars::RESULT_STACK[-1]{"="} = pos; }) )
        (? (?{; $Regexp::Grammars::RESULT_STACK[-1]{"="} = 1 + substr($_,0,pos) =~ tr/\n/\n/; }) )
    )
};
my $EPILOGUE_NC = $EPILOGUE;
   $EPILOGUE_NC =~ s{ ; .* ;;}{;}xms;


#=====[ MISCELLANEOUS PATTERNS THAT MATCH USEFUL THINGS ]========

# Match an identifier...
my $IDENT     = qr{ [^\W\d] \w*+ }xms;
my $QUALIDENT = qr{ (?: $IDENT :: )*+ $IDENT }xms;

# Match balanced parentheses, taking into account \-escapes and []-escapes...
my $PARENS = qr{
    (?&VAR_PARENS)
    (?(DEFINE)
        (? \( (?: \\. | (?&VAR_PARENS) | (?&CHARSET) | [^][()\\]++)*+ \) )
        (? \[ \^?+ \]?+ (?: \[:\w+:\] | \\. | [^]])*+ \] )

    )
}xms;

# Match a  directive within rules...
my $WS_PATTERN = qr{]++ | $PARENS )*+) >}xms;


#=====[ UTILITY SUBS FOR ERROR AND WARNING MESSAGES ]========

sub _uniq {
    my %seen;
    return grep { defined $_ && !$seen{$_}++ } @_;
}

# Default translator for error messages...
my $ERRORMSG_TRANSLATOR = sub {
    my ($errormsg, $rulename, $context) = @_;

    $rulename   = 'valid input' if $rulename eq q{};
    $context  //= '';

    # Unimplemented subrule when rulename starts with '-'...
    if (substr($rulename,0,1) eq '-') {
        $rulename = substr($rulename,1);
        return "Can't match subrule <$rulename> (not implemented)";
    }

    # Empty message converts to a "Expected...but found..." message...
    if ($errormsg eq q{}) {
        $rulename =~ tr/_/ /;
        $rulename = lc($rulename);
        return "Expected $rulename, but found '$context' instead";
    }

    # "Expecting..." messages get "but found" added...
    if (lc(substr($errormsg,0,6)) eq 'expect') {
        return "$errormsg, but found '$context' instead";
    }

    # Everything else stays "as is"...
    return $errormsg;
};

# Allow user to set translation...
sub set_error_translator {
    { package Regexp::Grammars::TranslatorRestorer;
      sub new {
        my ($class, $old_translator) = @_;
        bless \$old_translator, $class;
      }
      sub DESTROY {
        my ($old_translator_ref) = @_;
        $ERRORMSG_TRANSLATOR = ${$old_translator_ref};
      }
    }

    my ($translator_ref) = @_;
    die "Usage: set_error_translator(\$subroutine_reference)\n"
        if ref($translator_ref) ne 'CODE';

    my $old_translator_ref = $ERRORMSG_TRANSLATOR;
    $ERRORMSG_TRANSLATOR = $translator_ref;

    return defined wantarray
        ? Regexp::Grammars::TranslatorRestorer->new($old_translator_ref)
        : ();
}

# Dispatch to current translator for error messages...
sub _translate_errormsg {
    goto &{$ERRORMSG_TRANSLATOR};
}

#=====[ SUPPORT FOR TRANSLATING GRAMMAR-ENHANCED REGEX TO NATIVE REGEX ]====

# Store any specified grammars...
my %user_defined_grammar;

my %REPETITION_DESCRIPTION_FOR = (
    '+'  => 'once or more',
    '*'  => 'any number of times',
    '?'  => 'if possible',
    '+?' => 'as few times as possible',
    '*?' => 'as few times as possible',
    '??' => 'if necessary',
    '++' => 'as many times as possible',
    '*+' => 'as many times as possible',
    '?+' => 'if possible',
);

sub _translate_raw_regex {
    my ($regex, $debug_build, $debug_runtime) = @_;

    my $is_comment =  substr($regex, 0, 1) eq q{#}
                   || substr($regex, 0, 3) eq q{(?#};
    my $visible_regex = _squeeze_ws($regex);

    # Report how regex was interpreted, if requested to...
    if ($debug_build && $visible_regex ne q{} && $visible_regex ne q{ }) {
        _debug_notify( info =>
                           "   |",
                           "   |...Treating '$visible_regex' as:",
            ($is_comment ? "   |       \\ a comment (which will be ignored)"
                         : "   |       \\ normal Perl regex syntax"
            ),
        );
    }

    return q{} if $is_comment;

    # Generate run-time debugging code (if any)...
    my ($debug_pre, $debug_post)
        = _build_raw_debugging_statements($debug_runtime,$visible_regex, +1);

    # Replace negative lookahead with one that works under R::G...
    $regex =~ s{\(\?!}{(?!(?!)|}gxms;
    # ToDo: Also replace positive lookahead with one that works under R::G...
    #       This replacement should be of the form:
    #           $regex =~ s{\(\?!}{(?!(?!)|(?!(?!)|}gxms;
    #       but need to find a way to insert the extra ) at the other end

    return $debug_runtime && $regex eq '|'   ?  $regex . $debug_post
         : $debug_runtime && $regex =~ /\S/  ?  "(?#)(?:$debug_pre($regex)$debug_post(?#))"
         :                                      $regex;
}

# Report and convert a debugging directive...
sub _translate_debug_directive {
    my ($construct, $cmd, $debug_build) = @_;

    # Report how directive was interpreted, if requested to...
    if ($debug_build) {
        _debug_notify( info =>
            "   |",
            "   |...Treating $construct as:",
            "   |       \\ Change run-time debugging mode to '$cmd'",
        );
    }

    return qq{(?{; local \$Regexp::Grammars::DEBUG = q{$cmd}; }) };
}

# Report and convert a timeout directive...
sub _translate_timeout_directive {
    my ($construct, $timeout, $debug_build) = @_;

    # Report how directive was interpreted, if requested to...
    if ($debug_build) {
        _debug_notify( info =>
            "   |",
            "   |...Treating $construct as:",
         ($timeout > 0
          ? "   |       \\ Cause the entire parse to fail after $timeout second" .  ($timeout==1 ? q{} : q{s})
          : "   |       \\ Cause the entire parse to fail immediately"
         ),
        );
    }

    return $timeout > 0
            ? qq{(?{; local \$Regexp::Grammars::TIMEOUT = { duration => $timeout, limit => time() + $timeout }; }) }
            : qq{(*COMMIT)(*FAIL)};
}

# Report and convert a  directive...
sub _translate_require_directive {
    my ($construct, $condition, $debug_build) = @_;

    $condition = substr($condition, 3, -2);

    # Report how directive was interpreted, if requested to...
    if ($debug_build) {
        _debug_notify( info =>
            "   |",
            "   |...Treating $construct as:",
            "   |       \\ Require that {$condition} is true",
        );
    }

    my $quoted_condition = $condition;
    $quoted_condition =~ s{\$}{}xms;

    return qq{(?(?{;$condition})
        (?{;Regexp::Grammars::_debug_require(
            scalar \@Regexp::Grammars::RESULT_STACK, q{$quoted_condition}, 1)
                if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG}})
      | (?{;Regexp::Grammars::_debug_require(
            scalar \@Regexp::Grammars::RESULT_STACK, q{$quoted_condition}, 0)
                if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG}})(?!))
    };
}


# Report and convert a  directive...
sub _translate_minimize_directive {
    my ($construct, $debug_build) = @_;

    # Report how directive was interpreted, if requested to...
    if ($debug_build) {
        _debug_notify( info =>
            "   |",
            "   |...Treating $construct as:",
            "   |       \\ Minimize result value if possible",
        );
    }

    return q{(?{;
        if (1 == grep { $_ ne '!' && $_ ne '@' && $_ ne '~' } keys %MATCH) { # ...single alnum key
            local %Regexp::Grammars::matches = %MATCH;
            delete @Regexp::Grammars::matches{'!', '@', '~'};
            local ($Regexp::Grammars::only_key) = keys %Regexp::Grammars::matches;
            local $Regexp::Grammars::array_ref  = $MATCH{$Regexp::Grammars::only_key};
            if (ref($Regexp::Grammars::array_ref) eq 'ARRAY' && 1 == @{$Regexp::Grammars::array_ref}) {
                $MATCH = $Regexp::Grammars::array_ref->[0];
            }
        }
    })};
}

# Report and convert a debugging directive...
sub _translate_error_directive {
    my ($construct, $type, $msg, $debug_build, $subrule_name) = @_;
    $subrule_name //= 'undef';

    # Determine severity...
    my $severity = ($type eq 'error') ? 'fail' : 'non-fail';

    # Determine fatality (and build code to invoke it)...
    my $fatality = ($type eq 'fatal') ? '(*COMMIT)(*FAIL)' : q{};

    # Unpack message...
    if (substr($msg,0,3) eq '(?{') {
        $msg = 'do'. substr($msg,2,-1);
    }
    else {
        $msg = quotemeta $msg;
        $msg = qq{qq{$msg}};
    }

    # Report how directive was interpreted, if requested to...
    if ($debug_build) {
        _debug_notify( info => "   |",
                               "   |...Treating $construct as:",
            ( $type eq 'log' ? "   |       \\ Log a message to the logfile"
                             : "   |       \\ Append a $severity error message to \@!"
            ),
        );
    }

    # Generate the regex...
    return $type eq 'log'
        ? qq{(?{Regexp::Grammars::_debug_logmsg(scalar \@Regexp::Grammars::RESULT_STACK,$msg)
                if \$Regexp::Grammars::DEBUG_LEVEL{\$Regexp::Grammars::DEBUG}
          })}

        : qq{(?:(?{;local \$Regexp::Grammar::_memopos=pos();})
              (?>\\s*+((?-s).{0,$MAX_CONTEXT_WIDTH}+))
              (?{; pos() = \$Regexp::Grammar::_memopos;
              @! = Regexp::Grammars::_uniq(
                @!,
                Regexp::Grammars::_translate_errormsg($msg,q{$subrule_name},\$CONTEXT)
              ) }) (?!)|}
        . ($severity eq 'fail' ? q{(?!)} : $fatality)
        . q{)}
        ;
}

sub _translate_subpattern {
    my ($construct, $alias, $subpattern, $savemode, $postmodifier, $debug_build, $debug_runtime, $timeout, $backref)
        = @_;

    # Determine save behaviour...
    my $is_noncapturing   = $savemode eq 'noncapturing';
    my $is_listifying     = $savemode eq 'list';
    my $is_codeblock      = substr($subpattern,0,3) eq '(?{';
    my $value_saved       = $is_codeblock  ? '$^R'                    : '$^N';
    my $do_something_with = $is_codeblock  ? 'execute the code block' : 'match the pattern';
    my $result            = $is_codeblock  ? 'result'                 : 'matched substring';
    my $description       = $is_codeblock    ? substr($subpattern,2,-1)
                          : defined $backref ? $backref
                          :                    $subpattern;
    my $debug_construct
        = $is_codeblock ?  '<' . substr($alias,1,-1) . '= (?{;' . substr($subpattern,3,-2) . '})>'
        :                  $construct
        ;

    # Report how construct was interpreted, if requested to...
    my $repeatedly = $REPETITION_DESCRIPTION_FOR{$postmodifier} // q{};
    my $results  = $is_listifying && $postmodifier    ? "each $result"
                 : substr($postmodifier,0,1) eq '?'   ? "any $result"
                 : $postmodifier && !$is_noncapturing ? "only the final $result"
                 :                                      "the $result"
                 ;
    if ($debug_build) {
        _debug_notify( info =>
                                 "   |",
                                 "   |...Treating $construct as:",
                                 "   |      |  $do_something_with $description $repeatedly",
            ( $is_noncapturing ? "   |       \\ but don't save $results"
            : $is_listifying   ? "   |       \\ appending $results to \@{\$MATCH{$alias}}"
            :                    "   |       \\ saving $results in \$MATCH{$alias}"
            )
        );
    }

    # Generate run-time debugging code (if any)...
    my ($debug_pre, $debug_post)
        = _build_debugging_statements($debug_runtime,$debug_construct, +1);

    # Generate post-match result-capturing code, if match captures...
    my $post_action = $is_noncapturing
        ? q{}
        : qq{local \@Regexp::Grammars::RESULT_STACK = (
                \@Regexp::Grammars::RESULT_STACK[0..\@Regexp::Grammars::RESULT_STACK-2],
                Regexp::Grammars::_extend_current_result_frame_with_$savemode(
                    \\\@Regexp::Grammars::RESULT_STACK, $alias, $value_saved
                ),
            );}
        ;

    # Generate timeout test...
    my $timeout_test = $timeout ? q{(??{;Regexp::Grammars::_test_timeout()})} : q{};

    # Translate to standard regex code...
    return qq{$timeout_test(?{;local \@Regexp::Grammars::RESULT_STACK
                    = \@Regexp::Grammars::RESULT_STACK;$debug_pre})
                (?:($subpattern)(?{;$post_action$debug_post}))$postmodifier};
}


sub _translate_hashmatch {
    my ($construct, $alias, $hashname, $keypat, $savemode, $postmodifier, $debug_build, $debug_runtime, $timeout)
        = @_;

    # Empty or missing keypattern defaults to <.hk>...
    if (!defined $keypat || $keypat !~ /\S/) {
        $keypat = '(?&hk__implicit__)'
    }
    else {
        $keypat = substr($keypat, 1, -1);
    }

    # Determine save behaviour...
    my $is_noncapturing   = $savemode eq 'noncapturing';
    my $is_listifying     = $savemode eq 'list';

    # Convert hash to hash lookup...
    my $hash_lookup = '$' . substr($hashname, 1). '{$^N}';

    # Report how construct was interpreted, if requested to...
    my $repeatedly = $REPETITION_DESCRIPTION_FOR{$postmodifier} // q{};
    my $results  = $is_listifying && $postmodifier    ? 'each matched key'
                 : substr($postmodifier,0,1) eq '?'   ? 'any matched key'
                 : $postmodifier && !$is_noncapturing ? 'only the final matched key'
                 :                                      'the matched key'
                 ;
    if ($debug_build) {
        _debug_notify( info =>
                                 "   |",
                                 "   |...Treating $construct as:",
                                 "   |      |  match a key from the hash $hashname $repeatedly",
            ( $is_noncapturing ? "   |       \\ but don't save $results"
            : $is_listifying   ? "   |       \\ appending $results to \$MATCH{$alias}"
            :                    "   |       \\ saving $results in \$MATCH{$alias}"
            )
        );
    }

    # Generate run-time debugging code (if any)...
    my ($debug_pre, $debug_post)
        = _build_debugging_statements($debug_runtime,$construct, +1);

    # Generate post-match result-capturing code, if match captures...
    my $post_action = $is_noncapturing
        ? q{}
        : qq{local \@Regexp::Grammars::RESULT_STACK = (
                \@Regexp::Grammars::RESULT_STACK[0..\@Regexp::Grammars::RESULT_STACK-2],
                Regexp::Grammars::_extend_current_result_frame_with_$savemode(
                    \\\@Regexp::Grammars::RESULT_STACK, $alias, \$^N
                ),
            );}
        ;

    # Generate timeout test...
    my $timeout_test = $timeout ? q{(??{;Regexp::Grammars::_test_timeout()})} : q{};

    # Translate to standard regex code...
    return qq{$timeout_test(?:(?{;local \@Regexp::Grammars::RESULT_STACK
                    = \@Regexp::Grammars::RESULT_STACK;$debug_pre})
                (?:($keypat)(??{exists $hash_lookup ? q{} : q{(?!)}})(?{;$post_action$debug_post})))$postmodifier};
}


# Convert a " % " construct to pure Perl 5.10...
sub _translate_separated_list {
    my ($term, $op, $separator, $term_trans, $sep_trans,
        $ws, $debug_build, $debug_runtime, $timeout) = @_;

    # This insertion ensures backtracking upwinds the stack correctly...
    state $CHECKPOINT = q{(?{;@Regexp::Grammars::RESULT_STACK = @Regexp::Grammars::RESULT_STACK;})};

    # Translate meaningful whitespace...
    $ws = length($ws) ? q{(?&ws__implicit__)} : q{};

    # Generate support for optional trailing separator...
    my $opt_trailing = substr($op,-2) eq '%%' ? qq{$ws$sep_trans?}
                     :                          q{};

    # Generate timeout test...
    my $timeout_test = $timeout ? q{(??{;Regexp::Grammars::_test_timeout()})} : q{};

    # Report how construct was interpreted, if requested to...
    if ($debug_build) {
        _debug_notify( info =>
            "   |",
            "   |...Treating $term $op $separator as:",
            "   |      |  repeatedly match the subrule $term",
            "   |       \\ as long as the matches are separated by matches of $separator",
            (substr($op,-2) eq '%%' ?
            "   |        \\ and allowing an optional trailing $separator"
            : q{}
            )
        );
    }

    #  One-or-more...
    return qq{$timeout_test(?:$ws$CHECKPOINT$sep_trans$ws$term_trans)*$+$opt_trailing}
        if $op =~ m{ [*][*]() | [+]([+?]?) \s* %%?+ | \{ 1, \}([+?]?) \s* %%?+ }xms;

    #  Zero-or-more...
    return
    qq{{0}$timeout_test$ws(?:$term_trans(?:$ws$CHECKPOINT$sep_trans$ws$term_trans)*$+)?$+$opt_trailing}
        if $op =~ m{ [*]([+?]?) \s* %%? | \{ 0, \}([+?]?) \s* %%? }xms;

    #  One-or-zero...
    return qq{?$+$opt_trailing}
        if $op =~ m{ [?]([+?]?) \s* %%? | \{ 0,1 \}([+?]?) \s* %%? }xms;

    #  Zero exactly...
    return qq{{0}$ws$opt_trailing}
        if $op =~ m{ \{ 0 \}[+?]? \s* %%? }xms;

    #  N exactly...
    if ($op =~ m{ \{ (\d+) \}([+?]?) \s* %%? }xms ) {
        my $min = $1-1;
        return
        qq{{0}$timeout_test$ws(?:$term_trans(?:$ws$CHECKPOINT$sep_trans$ws$term_trans){$min}$+$opt_trailing)}
    }

    #  Zero-to-N...
    if ($op =~ m{ \{ 0,(\d+) \}([+?]?) \s* %%? }xms ) {
        my $max = $1-1;
        return
        qq{{0}$timeout_test$ws(?:$term_trans(?:$ws$CHECKPOINT$sep_trans$ws$term_trans){0,$max}$+)?$+$opt_trailing}
    }

    #  M-to-N and M-to-whatever...
    if ($op =~ m{ \{ (\d+),(\d*) \} ([+?]?) \s* %%? }xms ) {
        my $min = $1-1;
        my $max = $2 ? $2-1 : q{};
        return
        qq{{0}$timeout_test$ws(?:$term_trans(?:$ws$CHECKPOINT$sep_trans$ws$term_trans){$min,$max}$+$opt_trailing)}
    }

    # Somehow we missed a case (this should never happen)...
    die "Internal error: missing case in separated list handler";
}

sub _translate_subrule_call {
    my ($source_line, $source_file, $rulename, $grammar_name, $construct, $alias,
        $subrule, $args, $savemode, $postmodifier,
        $debug_build, $debug_runtime, $timeout, $valid_subrule_names_ref) = @_;

    # Translate arg list, if provided...
    my $arg_desc;
    if ($args eq q{}) {
        $args = q{()};
    }
    elsif (substr($args,0,3) eq '(?{') {
        # Turn parencode into do block...
        $arg_desc = substr($args,3,-2);
        substr($args,1,1) = 'do';
    }
    else {
        # Turn abbreviated format into a key=>value list...
        $args =~ s{ [(,] \s* \K : (\w+) (?= \s* [,)] ) }{$1 => \$MATCH{'$1'}}gxms;
        $arg_desc = substr($args,1,-1);
    }

    # Transform qualified subrule names...
    my $simple_subrule = $subrule;
    my $start_grammar = (($simple_subrule =~ s{(.*)::}{}xms) ? $1 : "");
    if ($start_grammar !~ /^NEXT$|::/) {
        $start_grammar = caller(3).'::'.$start_grammar;
    }

    my @candidates = $start_grammar eq 'NEXT' ? _ancestry_of($grammar_name)
                   :                            _ancestry_of($start_grammar);

    # Rename fully-qualified rule call, if to ancestor grammar...
    RESOLVING:
    for my $parent_class (@candidates) {
        my $inherited_subrule = $parent_class.'::'.$simple_subrule;
        if ($CACHE{$inherited_subrule}) {
            $subrule = $inherited_subrule;
            last RESOLVING;
        }
    }

    # Replace package separators, which regex engine can't handle...
    my $internal_subrule = $subrule;
    $internal_subrule =~ s{::}{_88_}gxms;

    # Shortcircuit if unknown subrule invoked...
    if (!$valid_subrule_names_ref->{$subrule}) {
        _debug_notify( error =>
            qq{Found call to $construct inside definition of $rulename},
            qq{near $source_file line $source_line.},
            qq{But no  or  was defined in the grammar},
            qq{(Did you misspell $construct? Or forget to define the rule?)},
            q{},
        );
        return "(?{Regexp::Grammars::_debug_fatal('$construct')})(*COMMIT)(*FAIL)";
    }

    # Determine save behaviour...
    my $is_noncapturing = $savemode =~ /noncapturing|lookahead/;
    my $is_listifying   = $savemode eq 'list';

    my $save_code =
       $is_noncapturing?
          q{ @Regexp::Grammars::RESULT_STACK[0..@Regexp::Grammars::RESULT_STACK-2] }
     : $is_listifying?
         qq{ \@Regexp::Grammars::RESULT_STACK[0..\@Regexp::Grammars::RESULT_STACK-3],
              Regexp::Grammars::_pop_current_result_frame_with_list(
                  \\\@Regexp::Grammars::RESULT_STACK, $alias, '$simple_subrule', \$^N
              ),
         }
     :
         qq{ \@Regexp::Grammars::RESULT_STACK[0..\@Regexp::Grammars::RESULT_STACK-3],
              Regexp::Grammars::_pop_current_result_frame(
                   \\\@Regexp::Grammars::RESULT_STACK, $alias, '$simple_subrule', \$^N
              ),
        }
     ;

    # Report how construct was interpreted, if requested to...
    my $repeatedly = $REPETITION_DESCRIPTION_FOR{$postmodifier} // q{};
    my $results  = $is_listifying && $postmodifier    ? 'each match'
                 : substr($postmodifier,0,1) eq '?'   ? 'any match'
                 :                                      'the match'
                 ;
    my $do_something_with = $savemode eq 'neglookahead' ? 'lookahead for anything except'
                          : $savemode eq 'poslookahead' ? 'lookahead for'
                          :                               'match'
                          ;
    if ($debug_build) {
        _debug_notify( info =>
                                 "   |",
                                 "   |...Treating $construct as:",
                                 "   |      |  $do_something_with the subrule <$subrule> $repeatedly",
            (defined $arg_desc ? "   |      |  passing the args: ($arg_desc)"
            :                    ()
            ),
            ( $is_noncapturing ? "   |       \\ but don't save anything"
            : $is_listifying   ? "   |       \\ appending $results to \$MATCH{$alias}"
            :                    "   |       \\ saving $results in \$MATCH{$alias}"
            ),
        );
    }

    # Generate post-match result-capturing code, if match captures...
    my ($debug_pre, $debug_post)
        = _build_debugging_statements($debug_runtime, $construct);

    # Generate timeout test...
    my $timeout_test = $timeout ? q{(??{;Regexp::Grammars::_test_timeout()})} : q{};

    # Translate to standard regex code...
    return qq{(?:$timeout_test(?{;
            local \@Regexp::Grammars::RESULT_STACK = (\@Regexp::Grammars::RESULT_STACK, {'\@'=>{$args}});
            $debug_pre})((?&$internal_subrule))(?{;
                local \@Regexp::Grammars::RESULT_STACK = (
                    $save_code
                );$debug_post
    }))$postmodifier};
}

sub _translate_rule_def {
    my ($type, $qualifier, $name, $callname, $qualname, $body, $objectify, $local_ws, $nocontext)
        = @_;
    $qualname =~ s{::}{_88_}gxms;

    # Return object if requested...
    my $objectification =
        $objectify ? qq{(??{; local \@Regexp::Grammars::RESULT_STACK = \@Regexp::Grammars::RESULT_STACK;
                            \$Regexp::Grammars::RESULT_STACK[-1] = '$qualifier$name'->can('new')
                                ? '$qualifier$name'->new(\$Regexp::Grammars::RESULT_STACK[-1])
                                : bless \$Regexp::Grammars::RESULT_STACK[-1], '$qualifier$name';
                            Regexp::Grammars::_debug_non_hash(\$Regexp::Grammars::RESULT_STACK[-1],'$name');
                        })}
                   : q{};

    # Each rule or token becomes a DEFINE'd Perl 5.10 named capture...
    my $implicit_version
        = ($callname eq 'ws' || $callname eq 'hk')
            ? qq{(?<${callname}__implicit__> $body) }
            : qq{};
    return qq{
        (?(DEFINE) $local_ws
            (?<$qualname>
            (?<$callname>
                (?{\@{\$Regexp::Grammars::RESULT_STACK[-1]}{'!','~'}=(\$#{!}, $nocontext);})
                (?:$body) $objectification
                (?{;\$#{!}=delete(\$Regexp::Grammars::RESULT_STACK[-1]{'!'})//0;
                           delete(\$Regexp::Grammars::RESULT_STACK[-1]{'\@'});
                })
            ))
            $implicit_version
        )
    };
}


# Locate any valid <...> sequences and replace with native regex code...
sub _translate_subrule_calls {
    my ($source_file, $source_line,
        $grammar_name,
        $grammar_spec,
        $compiletime_debugging_requested,
        $runtime_debugging_requested,
        $timeout_requested,
        $pre_match_debug,
        $post_match_debug,
        $rule_name,
        $subrule_names_ref,
        $magic_ws,
    ) = @_;

    my $pretty_rule_name = $rule_name ? ($magic_ws ? '"
                                      : 'main regex (before first rule)';

    # Remember the preceding construct, so as to implement the +% etc. operators...
    my $prev_construct   = q{};
    my $prev_translation = q{};
    my $curr_line_num = 1;

    # Translate all other calls (MAIN GRAMMAR FOR MODULE)...
    $grammar_spec =~ s{
    (?{ $curr_line_num = substr($_, 0, pos) =~ tr/\n//; })
      (? (? \s*+)  (? (?&SEPLIST_OP) ) (? \s*+) )?
      (?
        (?
        <
        (?:
            (?
                   \.                            \s* (?(?&QUALIDENT)) \s* (?(?&ARGLIST)) \s*
            )
          | (?
                   (? \? | \! )            \s* (?(?&QUALIDENT)) \s* (?(?&ARGLIST)) \s*
            )
          | (?
                                                 \s* (?(?&QUALIDENT)) \s* (?(?&ARGLIST)) \s*

            )
          | (?
                   \[                            \s* (?(?&QUALIDENT)) \s* (?(?&ARGLIST)) \s* \]
            )
          | (?
                       (?(?&IDENT)) \s* = \s* (?(?&QUALIDENT)) \s* (?(?&ARGLIST)) \s*

            )
          | (?
                   \[  (?(?&IDENT)) \s* = \s* (?(?&QUALIDENT)) \s* (?(?&ARGLIST)) \s* \]
            )

          | (?
                                                 \s* : (?(?&QUALIDENT)) \s*
            )
          | (?
                       (?(?&IDENT)) \s* = \s* : (?(?&QUALIDENT)) \s*
            )
          | (?
                   \[  (?(?&IDENT)) \s* = \s* : (?(?&QUALIDENT)) \s*  \]
            )

          | (?
                   \.  (?(?&IDENT)) \s* = \s* (?(?&PARENCODE)|(?&PARENS)|(?&LITERAL)) \s*
            )
          | (?
                       (?(?&IDENT)) \s* = \s* (?(?&PARENCODE)|(?&PARENS)|(?&LITERAL)) \s*
            )
          | (?
                   \[  (?(?&IDENT)) \s* = \s* (?(?&PARENCODE)|(?&PARENS)|(?&LITERAL)) \s* \]
            )
          | (?
                                                     (?(?&HASH)) \s* (?(?&BRACES))?  \s*
            )
          | (?
                       (?(?&IDENT)) \s* = \s* (?(?&HASH)) \s* (?(?&BRACES))?  \s*
            )
          | (?
                   \[  (?(?&IDENT)) \s* = \s* (?(?&HASH)) \s* (?(?&BRACES))?  \s* \]
            )
          | (?
                                                 \s* (? \\  | /) (? [:] (?&QUALIDENT))  \s*
                |                                \s* (? \\_ | /) (?     (?&QUALIDENT))  \s*
            )
          | (?
                       (?(?&IDENT)) \s* = \s* (? \\  | /) (? [:] (?&QUALIDENT))  \s*
                |      (?(?&IDENT)) \s* = \s* (? \\_ | /) (?     (?&QUALIDENT))  \s*
            )
          | (?
                   \[  (?(?&IDENT)) \s* = \s* (? \\  | /) (? [:] (?&QUALIDENT))  \s* \]
                |  \[  (?(?&IDENT)) \s* = \s* (? \\_ | /) (?     (?&QUALIDENT))  \s* \]
            )
          |
            (?
                    minimize \s* : \s*
            )
          |
            (?
                    require \s* : \s* (? (?&PARENCODE) ) \s*
            )
          |
            (?
                    debug \s* : \s* (? run | match | step | try | off | on) \s*
            )
          |
            (?
                    timeout \s* : \s* (? \d+) \s*
            )
          |
            (?
                    context \s* : \s*
            )
          |
            (?
                    nocontext \s* : \s*
            )
          |
            (?
                    [.][.][.]
                  | [!][!][!]
                  | [?][?][?]
            )
          |
            (?
                    (? error | fatal ) \s*+ : \s*+
            )
          |
            (?
                    (? log | error | warning | fatal )
                    \s*+ : \s*+
                    (? (?&PARENCODE) | .+? )
                    \s*+
            )
        )
        > (? \s* (?! (?&SEPLIST_OP) ) [?+*][?+]? | )
      |
        (?
            $WS_PATTERN
        )
      |
        (?
            (?&SEPLIST_OP) \s* (? \S* )
        )
      |
        (?
            \(\?\<\w+\>
        )
      |
        (?
            < [^>\n]* [>\n]
        )
      |
        (?
            (?
          | (?
        )
      |
        (?
            (?: \\[^shv]
            |   (?! (?&PARENCODE) ) (?&PARENS)
            |   (?&CHARSET)
            |   \w++
            |   \|
            )
            (?&QUANTIFIER)?
        )
      |
        (?
              \s++
            | \\. (?&QUANTIFIER)?
            | \(\?!
            | \(\?\# [^)]* \)   # (?# -> old style inline comment)
            | (?&PARENCODE)
            | \# [^\n]*+
            | [^][\s()<>#\\]++
        )
    )

    (?(DEFINE)
        (? \*\* | [*+?] [+?]?+ \s* %%?+ | \{ \d+(,\d*)? \} [+?]?+ \s* %%?+ )
        (?    \( (?:[?] (?: <[=!] | [:>] ))?
                         (?: \\. | (?&PARENCODE) | (?&PARENS) | (?&CHARSET) | [^][()\\<>]++ )*+
                      \)
        )
        (?    \{        (?: \\. | (?&BRACES)    | [^{}\\]++   )*+  \}   )
        (? \(\?\??\{ (?: \\. | (?&BRACES)    | [^{}\\]++   )*+  \}\) )
        (?      \% (?&IDENT) (?: :: (?&IDENT) )*                          )
        (?   \[ \^?+ \]?+ (?: \[:\w+:\] | \\. | [^]] )*+        \]     )
        (?     [^\W\d]\w*+                                               )
        (? (?: [^\W\d]\w*+ :: )*  [^\W\d]\w*+                        )
        (?   (?&NUMBER) | (?&STRING) | (?&VAR)                         )
        (?    [+-]? \d++ (?:\. \d++)? (?:[eE] [+-]? \d++)?              )
        (?    ' [^\\']++ (?: \\. [^\\']++ )* '                          )
        (?   (?&PARENCODE) | \( \s* (?&ARGS)? \s* \) | (?# NOTHING )   )
        (?      (?&ARG) \s* (?: , \s* (?&ARG) \s* )*  ,?                  )
        (?       (?&VAR)  |  (?&KEY) \s* => \s* (?&LITERAL)                )
        (?       : (?&IDENT)                                               )
        (?       (?&IDENT) | (?&LITERAL)                                   )
        (? [*+?][+?]? | \{ \d+,?\d* \} [+?]?                        )
    )
    }{
        my $curr_construct   = $+{construct};
        my $list_marker      = $+{list_marker} // q{};
        my $alias            = ($+{alias}//'MATCH') eq 'MATCH' ? q{'='} : qq{'$+{alias}'};

        # Determine and remember the necessary translation...
        my $curr_translation = do{

        # Translate subrule calls of the form: ...
            if (defined $+{alias_parens_scalar}) {
                my $pattern = substr($+{pattern},0,1) eq '(' ? $+{pattern} : "(?{$+{pattern}})";
                _translate_subpattern(
                    $curr_construct, $alias, $pattern, 'scalar', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested, $timeout_requested,
                );
            }
            elsif (defined $+{alias_parens_scalar_nocap}) {
                my $pattern = substr($+{pattern},0,1) eq '(' ? $+{pattern} : "(?{$+{pattern}})";
                _translate_subpattern(
                    $curr_construct, $alias, $pattern, 'noncapturing', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested, $timeout_requested,
                );
            }
            elsif (defined $+{alias_parens_list}) {
                my $pattern = substr($+{pattern},0,1) eq '(' ? $+{pattern} : "(?{$+{pattern}})";
                _translate_subpattern(
                    $curr_construct, $alias, $pattern, 'list', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested, $timeout_requested,
                );
            }

        # Translate subrule calls of the form: ...
            elsif (defined $+{alias_hash_scalar}) {
                _translate_hashmatch(
                    $curr_construct, $alias, $+{varname}, $+{keypat}, 'scalar', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                );
            }
            elsif (defined $+{alias_hash_scalar_nocap}) {
                _translate_hashmatch(
                    $curr_construct, $alias, $+{varname}, $+{keypat}, 'noncapturing', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                );
            }
            elsif (defined $+{alias_hash_list}) {
                _translate_hashmatch(
                    $curr_construct, $alias, $+{varname}, $+{keypat}, 'list', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                );
            }

        # Translate subrule calls of the form: ...
            elsif (defined $+{alias_subrule_scalar}) {
                _translate_subrule_call(
                    $source_line, $source_file,
                    $pretty_rule_name,
                    $grammar_name,
                    $curr_construct, $alias, $+{subrule}, $+{args}, 'scalar', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                    $subrule_names_ref,
                );
            }
            elsif (defined $+{alias_subrule_list}) {
                _translate_subrule_call(
                    $source_line, $source_file,
                    $pretty_rule_name,
                    $grammar_name,
                    $curr_construct, $alias, $+{subrule}, $+{args}, 'list', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                    $subrule_names_ref,
                );
            }

        # Translate subrule calls of the form:  and ...
            elsif (defined $+{self_subrule_lookahead}) {

                # Determine type of lookahead, and work around capture problem...
                my ($type, $pre, $post) = ( 'neglookahead', '(?!(?!)|', ')' );
                if ($+{sign} eq '?') {
                    $type = 'poslookahead';
                    $pre  x= 2;
                    $post x= 2;
                }

                $pre . _translate_subrule_call(
                    $source_line, $source_file,
                    $pretty_rule_name,
                    $grammar_name,
                    $curr_construct, qq{'$+{subrule}'}, $+{subrule}, $+{args}, $type, q{},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                    $subrule_names_ref,
                  )
                . $post;
            }
            elsif (defined $+{self_subrule_scalar_nocap}) {
                _translate_subrule_call(
                    $source_line, $source_file,
                    $pretty_rule_name,
                    $grammar_name,
                    $curr_construct, qq{'$+{subrule}'}, $+{subrule}, $+{args}, 'noncapturing', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                    $subrule_names_ref,
                );
            }
            elsif (defined $+{self_subrule_scalar}) {
                _translate_subrule_call(
                    $source_line, $source_file,
                    $pretty_rule_name,
                    $grammar_name,
                    $curr_construct, qq{'$+{subrule}'}, $+{subrule}, $+{args}, 'scalar', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                    $subrule_names_ref,
                );
            }
            elsif (defined $+{self_subrule_list}) {
                _translate_subrule_call(
                    $source_line, $source_file,
                    $pretty_rule_name,
                    $grammar_name,
                    $curr_construct, qq{'$+{subrule}'}, $+{subrule}, $+{args}, 'list', $+{modifier},
                    $compiletime_debugging_requested,
                    $runtime_debugging_requested,
                    $timeout_requested,
                    $subrule_names_ref,
                );
            }

        # Translate subrule calls of the form: ...
            elsif (defined $+{alias_argrule_scalar}) {
                my $pattern = qq{(??{;\$Regexp::Grammars::RESULT_STACK[-1]{'\@'}{'$+{subrule}'} // '(?!)'})};
                _translate_subpattern(
                    $curr_construct, $alias, $pattern, 'scalar', $+{modifier},
                    $compiletime_debugging_requested, $runtime_debugging_requested, $timeout_requested,
                    "in \$ARG{'$+{subrule}'}"
                );
            }
            elsif (defined $+{alias_argrule_list}) {
                my $pattern = qq{(??{;\$Regexp::Grammars::RESULT_STACK[-1]{'\@'}{'$+{subrule}'} // '(?!)'})};
                _translate_subpattern(
                    $curr_construct, $alias, $pattern, 'list', $+{modifier},
                    $compiletime_debugging_requested, $runtime_debugging_requested, $timeout_requested,
                    "in \$ARG{'$+{subrule}'}"
                );
            }

        # Translate subrule calls of the form: <:ARGNAME>...
            elsif (defined $+{self_argrule_scalar}) {
                my $pattern = qq{(??{;\$Regexp::Grammars::RESULT_STACK[-1]{'\@'}{'$+{subrule}'} // '(?!)'})};
                _translate_subpattern(
                    $curr_construct, qq{'$+{subrule}'}, $pattern, 'noncapturing', $+{modifier},
                    $compiletime_debugging_requested, $runtime_debugging_requested, $timeout_requested,
                    "in \$ARG{'$+{subrule}'}"
                );
            }

        # Translate subrule calls of the form: <\IDENT> or ...
            elsif (defined $+{backref} || $+{alias_backref} || $+{alias_backref_list}) {
                # Use "%ARGS" if subrule names starts with a colon...
                my $subrule = $+{subrule};
                if (substr($subrule,0,1) eq ':') {
                    substr($subrule,0,1,"\@'}{'");
                }

                my $backref = qq{\$Regexp::Grammars::RESULT_STACK[-1]{'$subrule'}};
                my $quoter  = $+{slash} eq '\\' || $+{slash} eq '\\_'
                                    ? "quotemeta($backref)"
                                    : "Regexp::Grammars::_invert_delim($backref)"
                                    ;
                my $pattern = qq{ (??{ defined $backref ? $quoter : q{(?!)}})};
                my $type = $+{backref}            ? 'noncapturing'
                         : $+{alias_backref}      ? 'scalar'
                         :                          'list'
                         ;
                _translate_subpattern(
                    $curr_construct, $alias, $pattern, $type, $+{modifier},
                    $compiletime_debugging_requested, $runtime_debugging_requested, $timeout_requested,
                    "in \$MATCH{'$subrule'}"
                );
            }

        # Translate reportable raw regexes (add debugging support)...
            elsif (defined $+{reportable_raw_regex}) {
                _translate_raw_regex(
                    $+{reportable_raw_regex}, $compiletime_debugging_requested, $runtime_debugging_requested
                );
            }

        # Translate too-complex repetition specifications...
            elsif (defined $+{complex_repetition}) {
                my ($repetition, $separator) = @+{'complex_repetition', 'complex_separator'};
                my ($metaop) = $repetition =~ m{(%%?)};
                my $quotedop = quotemeta($metaop);
                $separator =~ s/\s+/ /g;
                my $problem = $separator =~ /\S/
                    ? ["The $separator... separator you specified after the $metaop is too complex",
                       "(Try refactoring it into a single subrule call)",
                      ]
                    : ["No separator was specified after the $metaop",
                       "(Or did you need a $quotedop instead, to match a literal '$metaop'?)",
                      ];
                _debug_notify( fatal =>
                    "Invalid separation specifier: $metaop",
                    "at line $curr_line_num of $pretty_rule_name",
                    @{$problem},
                );
                exit(1);
            }

        # Translate non-reportable raw regexes (leave as is)...
            elsif (defined $+{raw_regex}) {
                # Handle raw % and %%
                my $raw_regex = $+{raw_regex};
                if ($raw_regex =~ / \A %%?+ /x) {
                    _debug_notify( fatal =>
                        "Invalid separation specifier: $&",
                        "at line $curr_line_num of $pretty_rule_name",
                        "(Did you forget to put a repetition quantifier before the $&",
                        " or did you need a " . quotemeta($&) . " instead, to match a literal '$&'?)",
                    );
                    exit(1);
                }

                # Handle any other raw regex...
                _translate_raw_regex(
                    $raw_regex, $compiletime_debugging_requested
                );
            }

        # Translate directives...
            elsif (defined $+{require_directive}) {
                _translate_require_directive(
                    $curr_construct, $+{condition}, $compiletime_debugging_requested
                );
            }
            elsif (defined $+{minimize_directive}) {
                _translate_minimize_directive(
                    $curr_construct, $+{condition}, $compiletime_debugging_requested
                );
            }
            elsif (defined $+{debug_directive}) {
                _translate_debug_directive(
                    $curr_construct, $+{cmd}, $compiletime_debugging_requested
                );
            }
            elsif (defined $+{timeout_directive}) {
                _translate_timeout_directive(
                    $curr_construct, $+{timeout}, $compiletime_debugging_requested
                );
            }
            elsif (defined $+{error_directive}) {
                _translate_error_directive(
                    $curr_construct, $+{error_type}, $+{msg},
                    $compiletime_debugging_requested, $rule_name
                );
            }
            elsif (defined $+{autoerror_directive}) {
                _translate_error_directive(
                    $curr_construct, $+{error_type}, q{},
                    $compiletime_debugging_requested, $rule_name
                );
            }
            elsif (defined $+{yadaerror_directive}) {
                _translate_error_directive(
                    $curr_construct,
                    ($+{yadaerror_directive} eq '???' ?  'warning' : 'error'),
                    q{},
                    $compiletime_debugging_requested, -$rule_name
                );
            }
            elsif (defined $+{context_directive}) {
                if ($compiletime_debugging_requested) {
                    _debug_notify( info => "   |",
                                           "   |...Treating $curr_construct as:",
                                           "   |       \\ Turn on context-saving for the current rule"
                    );
                }
                q{};  # Remove the directive
            }
            elsif (defined $+{nocontext_directive}) {
                if ($compiletime_debugging_requested) {
                    _debug_notify( info => "   |",
                                           "   |...Treating $curr_construct as:",
                                           "   |       \\ Turn off context-saving for the current rule"
                    );
                }
                q{};  # Remove the directive
            }
            elsif (defined $+{ws_directive}) {
                if ($compiletime_debugging_requested) {
                    _debug_notify( info => "   |",
                                           "   |...Treating $curr_construct as:",
                                           "   |       \\ Change whitespace matching for the current rule"
                    );
                }
                $curr_construct;
            }

        # Something that looks like a rule call or directive, but isn't...
            elsif (defined $+{incomplete_request}) {
                my $request = $+{incomplete_request};
                $request =~ s/\n//g;
                if ($request =~ /\A\s*<\s*\Z/) {
                    _debug_notify( fatal =>
                        qq{Invalid < metacharacter near line $curr_line_num of $pretty_rule_name},
                        qq{If you meant to match a literal '<', use: \\<},
                    );
                }
                else {
                    _debug_notify( fatal =>
                        qq{Possible failed attempt to specify},
                        qq{a subrule call or directive:  $request},
                        qq{near line $curr_line_num of $pretty_rule_name},
                        qq{If you meant to match literally, use: \\$request},
                    );
                }
                exit(1);
            }

        # A quantifier that isn't quantifying anything...
            elsif (defined $+{loose_quantifier}) {
                my $quant = $+{loose_quantifier};
                   $quant =~ s{^\s+}{};
                my $literal = quotemeta($quant);
                _debug_notify( fatal =>
                    qq{Quantifier that doesn't quantify anything: $quant},
                    qq{at line $curr_line_num in declaration of $pretty_rule_name},
                    qq{(Did you mean to match literally? If so, try: $literal)},
                    q{},
                );
                exit(1);
            }

        # There shouldn't be any other possibility...
            else {
                die qq{Internal error: this shouldn't happen!\n},
                    qq{Near '$curr_construct' at $curr_line_num of $pretty_rule_name\n};
            }
        };

        # Handle the **/*%/*%%/+%/{n,m}%/etc operators...
        if ($list_marker) {
            my $ws = $magic_ws ? $+{ws1} . $+{ws2} : q{};
            my $op = $+{op};

            $curr_translation = _translate_separated_list(
                $prev_construct,   $op, $curr_construct,
                $prev_translation, $curr_translation, $ws,
                $compiletime_debugging_requested,
                $runtime_debugging_requested, $timeout_requested,
            );
            $curr_construct = qq{$prev_construct $op $curr_construct};
        }

        # Finally, remember this latest translation, and return it...
        $prev_construct   = $curr_construct;
        $prev_translation = $curr_translation;;
    }exmsg;

    # Translate magic hash accesses...
    $grammar_spec =~ s{\$(?:\:\:)?MATCH (?= \s*\{) }
                      {\$Regexp::Grammars::RESULT_STACK[-1]}xmsg;
    $grammar_spec =~ s{\$(?:\:\:)?ARG (?= \s*\{) }
                      {\$Regexp::Grammars::RESULT_STACK[-1]{'\@'}}xmsg;

    # Translate magic scalars and hashes...
    state $translate_scalar = {
        q{%$MATCH}  => q{%{$Regexp::Grammars::RESULT_STACK[-1]{q{=}}}},
        q{@$MATCH}  => q{@{$Regexp::Grammars::RESULT_STACK[-1]{q{=}}}},
        q{$MATCH}   => q{$Regexp::Grammars::RESULT_STACK[-1]{q{=}}},
        q{%MATCH}   => q{%{$Regexp::Grammars::RESULT_STACK[-1]}},
        q{$CAPTURE} => q{$^N},
        q{$CONTEXT} => q{$^N},
        q{$DEBUG}   => q{$Regexp::Grammars::DEBUG},
        q{$INDEX}   => q{${\\pos()}},
        q{%ARG}     => q{%{$Regexp::Grammars::RESULT_STACK[-1]{'@'}}},

        q{%$::MATCH}  => q{%{$Regexp::Grammars::RESULT_STACK[-1]{q{=}}}},
        q{@$::MATCH}  => q{@{$Regexp::Grammars::RESULT_STACK[-1]{q{=}}}},
        q{$::MATCH}   => q{$Regexp::Grammars::RESULT_STACK[-1]{q{=}}},
        q{%::MATCH}   => q{%{$Regexp::Grammars::RESULT_STACK[-1]}},
        q{$::CAPTURE} => q{$^N},
        q{$::CONTEXT} => q{$^N},
        q{$::DEBUG}   => q{$Regexp::Grammars::DEBUG},
        q{$::INDEX}   => q{${\\pos()}},
        q{%::ARG}     => q{%{$Regexp::Grammars::RESULT_STACK[-1]{'@'}}},

    };
    state $translatable_scalar
        = join '|', map {quotemeta $_}
                        sort {length $b <=> length $a}
                             keys %{$translate_scalar};

    $grammar_spec =~ s{ ($translatable_scalar) (?! \s* (?: \[ | \{) ) }
                      {$translate_scalar->{$1}}oxmsg;

    return $grammar_spec;
}

# Generate a "decimal timestamp" and insert in a template...
sub _timestamp {
    my ($template) = @_;

    # Generate and insert any timestamp...
    if ($template =~ /%t/) {
        my ($sec, $min, $hour, $day, $mon,   $year) = localtime;
                                     $mon++; $year+=1900;
        my $timestamp = sprintf("%04d%02d%02d.%02d%02d%02d",
                                $year, $mon, $day, $hour, $min, $sec);
        $template =~ s{%t}{$timestamp}xms;;
    }

    return $template;
}

# Open (or re-open) the requested log file...
sub _autoflush {
    my ($fh) = @_;
    my $originally_selected = select $fh;
    $|=1;
    select $originally_selected;
}

sub _open_log {
    my ($mode, $filename, $from_where) = @_;
    $from_where //= q{};

    # Special case: '-' --> STDERR
    if ($filename eq q{-}) {
        return *STDERR{IO};
    }
    # Otherwise, just open the named file...
    elsif (open my $fh, $mode, $filename) {
        _autoflush($fh);
        return $fh;
    }
    # Otherwise, generate a warning and default to STDERR...
    else {
        local *Regexp::Grammars::LOGFILE = *STDERR{IO};
        _debug_notify( warn =>
            qq{Unable to open log file '$filename'},
            ($from_where ? $from_where : ()),
            qq{($!)},
            qq{Defaulting to STDERR instead.},
            q{},
        );
        return *STDERR{IO};
    }
}

sub _invert_delim {
    my ($delim) = @_;
    $delim = reverse $delim;
    $delim =~ tr/<>[]{}()??`'/><][}{)(??'`/;
    return quotemeta $delim;
}

# Regex to detect if other regexes contain a grammar specification...
my $GRAMMAR_DIRECTIVE
    = qr{ < grammar: \s* (? $QUALIDENT ) \s* > }xms;

# Regex to detect if other regexes contain a grammar inheritance...
my $EXTENDS_DIRECTIVE
    = qr{ < extends: \s* (? $QUALIDENT ) \s* > }xms;

# Cache of rule/token names within defined grammars...
my %subrule_names_for;

# Build list of ancestors for a given grammar...
sub _ancestry_of {
    my ($grammar_name) = @_;

    return () if !$grammar_name;

    use mro;
    return map { substr($_, $CACHE_LEN) } @{mro::get_linear_isa($CACHE.$grammar_name, 'c3')};
}

# Detect and translate any requested grammar inheritances...
sub _extract_inheritances {
    my ($source_line, $source_file, $regex, $compiletime_debugging_requested, $derived_grammar_name) = @_;


    # Detect and remove inheritance requests...
    while ($regex =~ s{$EXTENDS_DIRECTIVE}{}xms) {
        # Normalize grammar name and report...
        my $orig_grammar_name = $+{base_grammar_name};
        my $grammar_name = $orig_grammar_name;
        if ($grammar_name !~ /::/) {
            $grammar_name = caller(2).'::'.$grammar_name;
        }

        if (exists $user_defined_grammar{$grammar_name}) {
            if ($compiletime_debugging_requested) {
                _debug_notify( info =>
                    "Processing inheritance request for $grammar_name...",
                    q{},
                );
            }

            # Specify new relationship...
            no strict 'refs';
            push @{$CACHE.$derived_grammar_name.'::ISA'}, $CACHE.$grammar_name;
        }
        else {
            _debug_notify( fatal =>
                "Inheritance from unknown grammar requested",
                "by  directive",
                "in regex grammar declared at $source_file line $source_line",
                q{},
            );
            exit(1);
        }
    }

    # Retrieve ancestors (but not self) in C3 dispatch order...
    my (undef, @ancestors) = _ancestry_of($derived_grammar_name);

    # Extract subrule names and implementations for ancestors...
    my %subrule_names = map { %{$subrule_names_for{$_}} } @ancestors;
    $_ = -1 for values %subrule_names;
    my $implementation
        = join "\n", map { $user_defined_grammar{$_} } @ancestors;

    return $implementation, \%subrule_names;
}

# Transform grammar-augmented regex into pure Perl 5.10 regex...
sub _build_grammar {
    my ($grammar_spec) = @_;
    $grammar_spec .= q{};

    # Check for lack of Regexp::Grammar-y constructs and short-circuit...
    if ($grammar_spec !~ m{ < (?: [.?![:%\\/]? [^\W\d]\w* [^>]* | [.?!]{3} ) > }xms) {
        return $grammar_spec;
    }

    # Remember where we parked...
    my ($source_file, $source_line) = (caller 1)[1,2];
    $source_line -= $grammar_spec =~ tr/\n//;

    # Check for dubious repeated  constructs that throw away captures...
    my $dubious_line = $source_line;
    while ($grammar_spec =~ m{
           (.*?)
           (
            < (?! \[ )                     # not <[SUBRULE]>
                ( $IDENT (?: = [^>]*)? )   # but  or
            > \s*
            (                              # followed by a quantifier...
                [+*][?+]?                  #    either symbolic
              | \{\d+(?:,\d*)?\}[?+]?      #    or numeric
            )
           )
        }gxms) {
            my ($prefix, $match, $rule, $qual) = ($1, $2, $3, $4);
            $dubious_line += $prefix =~ tr/\n//;
            _debug_notify( warn =>
                qq{Repeated subrule <$rule>$qual},
                qq{at $source_file line $dubious_line},
                qq{will only capture its final match},
                qq{(Did you mean <[$rule]>$qual instead?)},
                q{},
            );
            $dubious_line += $match =~ tr/\n//;
    }

    # Check for dubious non-backtracking  constructs...
    $dubious_line = $source_line;
    while (
        $grammar_spec =~ m{
            (.*?)
            (
                <
                    (?! (?:obj)? (?:rule: | token ) )
                    ( [^>]+ )
                >
                \s*
                ( [?+*][+] | \{.*\}[+] )
            )
        }gxms) {
            my ($prefix, $match, $rule, $qual) = ($1, $2, $3, $4);
            $dubious_line += $prefix =~ tr/\n//;
            my $safe_qual = substr($qual,0,-1);
            _debug_notify( warn =>
                qq{Non-backtracking subrule call <$rule>$qual},
                qq{at $source_file line $dubious_line},
                qq{may not revert correctly during backtracking.},
                qq{(If grammar does not work, try <$rule>$safe_qual instead)},
                q{},
            );
            $dubious_line += $match =~ tr/\n//;
    }

    # Check whether a log file was specified...
    my $compiletime_debugging_requested;
    local *Regexp::Grammars::LOGFILE = *Regexp::Grammars::LOGFILE;
    my $logfile = q{-};

    my $log_where = "for regex grammar defined at $source_file line $source_line";
    $grammar_spec =~ s{ ^ [^#]* < logfile: \s* ([^>]+?) \s* > }{
        $logfile = _timestamp($1);

        # Presence of  implies compile-time logging...
        $compiletime_debugging_requested = 1;
        *Regexp::Grammars::LOGFILE = _open_log('>',$logfile, $log_where );

        # Delete  directive...
        q{};
    }gexms;

    # Look ahead for any run-time debugging or timeout requests...
    my $runtime_debugging_requested
        = $grammar_spec =~ m{
              ^ [^#]*
              < debug: \s* (run | match | step | try | on | same ) \s* >
            | \$DEBUG (?! \s* (?: \[ | \{) )
        }xms;

    my $timeout_requested
        = $grammar_spec =~ m{
              ^ [^#]*
              < timeout: \s* \d+ \s* >
        }xms;


    # Standard actions set up and clean up any regex debugging...
    # Before entire match, set up a stack of attempt records and report...
    my $pre_match_debug
        = $runtime_debugging_requested
            ? qq{(?{; *Regexp::Grammars::LOGFILE
                        = Regexp::Grammars::_open_log('>>','$logfile', '$log_where');
                      Regexp::Grammars::_init_try_stack(); })}
            : qq{(?{; *Regexp::Grammars::LOGFILE
                        = Regexp::Grammars::_open_log('>>','$logfile', '$log_where'); })}
            ;

    # After entire match, report whether successful or not...
    my $post_match_debug
        = $runtime_debugging_requested
            ? qq{(?{;Regexp::Grammars::_debug_matched(0,\\%/,'',\$^N)})
                |(?>(?{;Regexp::Grammars::_debug_handle_failures(0,''); }) (?!))
                }
            : q{}
            ;

    # Remove comment lines...
    $grammar_spec =~ s{^ ([^#\n]*) \s \# [^\n]* }{$1}gxms;

    # Subdivide into rule and token definitions, preparing to process each...
    # REWRITE THIS, USING (PROBABLY NEED TO REFACTOR ALL GRAMMARS TO REUSe
    # THESE COMPONENTS:
    #   (? \( \s* (?&PARAMS)? \s* \) | (?# NOTHING )                                          )
    #   (?    (?&PARAM) \s* (?: , \s* (?&PARAM) \s* )*  ,?                                       )
    #   (?     (?&VAR) (?: \s* = \s* (?: (?&LITERAL) | (?&PARENCODE) ) )?                         )
    #   (?   (?&NUMBER) | (?&STRING) | (?&VAR)                                                  )
    #   (?       : (?&IDENT)                                                                        )
    my @defns = split m{
            (< (obj|)(rule|token) \s*+ :
              \s*+ ((?:${IDENT}::)*+) (?: ($IDENT) \s*+ = \s*+ )?+
              ($IDENT)
            \s* >)
        }xms, $grammar_spec;

    # Extract up list of names of defined rules/tokens...
    # (Name is every 6th item out of every seven, skipping the first item)
    my @subrule_names = @defns[ map { $_ * 7 + 6 } 0 .. ((@defns-1)/7-1) ];
    my @defns_copy = @defns[1..$#defns];
    my %subrule_names;

    # Build a look-up table of subrule names, checking for duplicates...
    my $defn_line = $source_line + $defns[0] =~ tr/\n//;
    my %first_decl_explanation;
    for my $subrule_name (@subrule_names) {
        my ($full_decl, $objectify, $type, $qualifier, $name, $callname, $body) = splice(@defns_copy, 0, 7);
        if (++$subrule_names{$subrule_name} > 1) {
            _debug_notify( warn =>
                "Redeclaration of <$objectify$type: $subrule_name>",
                "at $source_file line $defn_line",
                "will be ignored.",
                @{ $first_decl_explanation{$subrule_name} },
                q{},
            );
        }
        else {
            $first_decl_explanation{$subrule_name} = [
                "(Hidden by the earlier declaration of <$objectify$type: $subrule_name>",
                " at $source_file line $defn_line)"
            ];
        }
        $defn_line += ($full_decl.$body) =~ tr/\n//;
    }

    # Add the built-ins...
    @subrule_names{'ws', 'hk', 'matchpos', 'matchline'} = (1) x 4;

    # An empty main rule will never match anything...
    my $main_regex = shift @defns;
    if ($main_regex =~ m{\A (?: \s++ | \(\?\# [^)]* \) | \# [^\n]++ )* \z}xms) {
        _debug_notify( error =>
            "No main regex specified before rule definitions",
            "in regex grammar declared at $source_file line $source_line",
            "Grammar will never match anything.",
            "(Or did you forget a  specification?)",
            q{},
        );
    }

    # Compile the regex or grammar...
    my $regex = q{};
    my $grammar_name;
    my $is_grammar;

    # Is this a grammar specification?
    if ($main_regex =~ $GRAMMAR_DIRECTIVE) {
        # Normalize grammar name and report...
        $grammar_name = $+{grammar_name};
        if ($grammar_name !~ /::/) {
            $grammar_name = caller(1) . "::$grammar_name";
        }
        $is_grammar = 1;

        # Add subrule definitions to namespace...
        for my $subrule_name (@subrule_names) {
            $CACHE{$grammar_name.'::'.$subrule_name} = 1;
        }
    }
    else {
        state $dummy_grammar_index = 0;
        $grammar_name = '______' . $dummy_grammar_index++;
    }

    # Extract any inheritance information...
    my ($inherited_rules, $inherited_subrule_names)
        = _extract_inheritances(
            $source_line, $source_file,
            $main_regex,
            $compiletime_debugging_requested,
            $grammar_name
          );

    # Remove  requests...
    $main_regex =~ s{ $EXTENDS_DIRECTIVE }{}gxms;

    # Add inherited subrule names to allowed subrule names;
    @subrule_names{ keys %{$inherited_subrule_names} }
        = values %{$inherited_subrule_names};

    # Remove comments from top-level grammar...
    $main_regex =~ s{
          \(\?\# [^)]* \)
        | (?
    }{}gxms;

    # Remove any top-level nocontext directive...
                    # 1 2     3     4
    $main_regex =~ s{^( (.*?) (\\*) (\# [^\n]*) )$}{length($3) % 2 ? $1 : $2.substr($3,0,-1)}gexms;
    my $nocontext = ($main_regex =~ s{ < nocontext \s* : \s* > }{}gxms) ? 1
                  : ($main_regex =~ s{ <   context \s* : \s* > }{}gxms) ? 0
                  :                                                       0;

    # If so, set up to save the grammar...
    if ($is_grammar) {
        # Normalize grammar name and report...
        if ($grammar_name !~ /::/) {
            $grammar_name = caller(1) . "::$grammar_name";
        }
        if ($compiletime_debugging_requested) {
            _debug_notify( info =>
                "Processing definition of grammar $grammar_name...",
                q{},
            );
        }

        # Remove the grammar directive...
        $main_regex =~ s{
            ( $GRAMMAR_DIRECTIVE
            | < debug: \s* (run | match | step | try | on | off | same ) \s* >
            )
        }{$source_line += $1 =~ tr/\n//; q{}}gexms;

        # Check for anything else in the main regex...
        if ($main_regex =~ /\A(\s*)\S/) {
            $source_line += $1 =~ tr/\n//;
            _debug_notify( warn =>
                "Unexpected item before first subrule specification",
                "in definition of ",
                "at $source_file line $source_line:",
                map({ "    $_"} grep /\S/, split "\n", $main_regex),
                "(this will be ignored when defining the grammar)",
                q{},
            );
        }

        # Remember set of valid subrule names...
        $subrule_names_for{$grammar_name}
            = {
                map({ ($_ => 1) } keys %subrule_names),
                map({ ($grammar_name.'::'.$_ => 1) } grep { !/::/ } keys %subrule_names),
              };
    }
    else { #...not a grammar specification
        # Report how main regex was interpreted, if requested to...
        if ($compiletime_debugging_requested) {
            _debug_notify( info =>
                "Processing the main regex before any rule definitions",
            );
        }

        # Any actual regex is processed first...
        $regex = _translate_subrule_calls(
            $source_file, $source_line,
            $grammar_name,
            $main_regex,
            $compiletime_debugging_requested,
            $runtime_debugging_requested,
            $timeout_requested,
            $pre_match_debug,
            $post_match_debug,
            q{},                        # Expected...what?
            \%subrule_names,
            0,                          # Whitespace isn't magical
        );

        # Wrap the main regex (to ensure |'s don't segment pre and # post commands)...
        $regex = "(?:$regex)";

        # Report how construct was interpreted, if requested to...
        if ($compiletime_debugging_requested) {
            _debug_notify( q{} =>
                q{   |},
                q{    \\___End of main regex},
                q{},
            );
        }
    }

    # Update line number...
    $source_line += $main_regex =~ tr/\n//;

    #  Then iterate any following rule definitions...
    while (@defns) {
        # Grab details of each rule defn (as extracted by previous split)...
        my ($full_decl, $objectify, $type, $qualifier, $name, $callname, $body) = splice(@defns, 0, 7);
        $name //= $callname;
        my $qualified_name = $grammar_name.'::'.$callname;

        # Report how construct was interpreted, if requested to...
        if ($compiletime_debugging_requested) {
            _debug_notify( info =>
                "Defining a $type: <$callname>",
                "   |...Returns: " . ($objectify ? "an object of class '$qualifier$name'" : "a hash"),
            );
        }

        my $local_nocontext
            = ($body =~ s{ < nocontext \s* : \s* > }{}gxms) ? 1
            : ($body =~ s{ <   context \s* : \s* > }{}gxms) ? 0
            :                                                 $nocontext;

        # Translate any nested <...> constructs...
        my $trans_body = _translate_subrule_calls(
            $source_file, $source_line,
            $grammar_name,
            $body,
            $compiletime_debugging_requested,
            $runtime_debugging_requested,
            $timeout_requested,
            $pre_match_debug,
            $post_match_debug,
            $callname,                # Expected...what?
            \%subrule_names,
            $type eq 'rule',          # Is whitespace magical?
        );

        # Report how construct was interpreted, if requested to...
        if ($compiletime_debugging_requested) {
            _debug_notify( q{} =>
                q{   |},
                q{    \\___End of rule definition},
                q{},
            );
        }

        # Make allowance for possible local whitespace definitions...
        my $local_ws_defn = q{};
        my $local_ws_call = q{(?&ws__implicit__)};

        # Rules make non-code literal whitespace match textual whitespace...
        if ($type eq 'rule') {
            # Implement any local whitespace definition...
            my $first_ws = 1;
            WS_DIRECTIVE:
            while ($trans_body =~ s{$WS_PATTERN}{}oxms) {
                my $defn = $1;
                if ($defn !~ m{\S}xms) {
                    _debug_notify( warn =>
                        qq{Ignoring useless empty  directive},
                        qq{in definition of },
                        qq{near $source_file line $source_line},
                        qq{(Did you mean  instead?)},
                        q{},
                    );
                    next WS_DIRECTIVE;
                }
                elsif (!$first_ws) {
                    _debug_notify( warn =>
                        qq{Ignoring useless extra  directive},
                        qq{in definition of },
                        qq{at $source_file line $source_line},
                        qq{(No more than one is permitted per rule!)},
                        q{},
                    );
                    next WS_DIRECTIVE;
                }
                else {
                    $first_ws = 0;
                }
                state $ws_counter = 0;
                $ws_counter++;
                $local_ws_defn = qq{(?<__RG_ws_$ws_counter> $defn)};
                $local_ws_call = qq{(?&__RG_ws_$ws_counter)};
            }

            # Implement auto-whitespace...
            state $CODE_OR_SPACE = qr{
                (?          # These are not magic...
                    \( \?\?? (?&BRACED) \)   #     Embedded code blocks
                  | \s++                     #     Whitespace not followed by...
                    (?= \|                   #         ...an OR
                      | \(\?\#\)             #         ...a null comment
                      | (?: \) \s* )? \z     #         ...the end of the rule
                      | \(\(?\?\&ws\)        #         ...an explicit ws match
                      | \(\?\??\{            #         ...an embedded code block
                      | \\[shv]              #         ...an explicit space match
                    )
                )
                |
                (? \s++ )       # All other whitespace is magic

                (?(DEFINE) (? \{ (?: \\. | (?&BRACED) | [^{}] )* \} ) )
            }xms;
            $trans_body =~ s{($CODE_OR_SPACE)}{ $+{ignorable_space} // $local_ws_call }exmsg;
        }
        else {
            while ($trans_body =~ s{$WS_PATTERN}{}oxms) {
                _debug_notify( warn =>
                    qq{Ignoring useless  directive},
                    qq{in definition of },
                    qq{at $source_file line $source_line},
                    qq{(Did you need to define  instead of ?)},
                    q{},
                );
            }
        }

        $regex
            .= "\n###############[ $source_file line $source_line ]###############\n"
            .  _translate_rule_def(
                 $type, $qualifier, $name, $callname, $qualified_name, $trans_body, $objectify,
                 $local_ws_defn, $local_nocontext,
               );

        # Update line number...
        $source_line += ($full_decl.$body) =~ tr/\n//;
    }

    # Insert checkpoints into any user-defined code block...
    $regex =~ s{ \( \?\?? \{ \K (?!;) }{
        local \@Regexp::Grammars::RESULT_STACK = \@Regexp::Grammars::RESULT_STACK;
    }xmsg;

    # Check for any suspicious left-overs from the start of the regex...
    pos $regex = 0;

    # If a grammar definition, save grammar and return a placeholder...
    if ($is_grammar) {
        $user_defined_grammar{$grammar_name} = $regex;
        return qq{(?{
            warn "Can't match directly against a pure grammar: \n";
        })(*COMMIT)(?!)};
    }
    # Otherwise, aggregrate the final grammar...
    else {
        return _complete_regex($regex.$inherited_rules, $pre_match_debug, $post_match_debug, $nocontext);
    }
}

sub _complete_regex {
    my ($regex, $pre_match_debug, $post_match_debug, $nocontext) = @_;

    return $nocontext ? qq{(?x)$pre_match_debug$PROLOGUE$regex$EPILOGUE_NC$post_match_debug}
                      : qq{(?x)$pre_match_debug$PROLOGUE$regex$EPILOGUE$post_match_debug};
}

1; # Magic true value required at end of module

__END__