Just for kicks I modified A sub named ∃ but added magic so "\x{2203}" =~ /\p{IdContinue}/ would be true and my hoped for character would be recognized as an identifier. I didn't work but it was kind of interesting to both write a source filter this way and to modify perl's idea of what constituted a unicode character class. I thought I'd share.

BEGIN {

    # Install a function which inserts the two codepoints
    # 2203;THERE EXISTS;Sm;0;ON;;;;;Y;;;;;
    # 2204;THERE DOES NOT EXIST;Sm;0;ON;2203 0338;;;;Y;;;;;

    unshift @INC, sub {
        my ( $self, $module ) = @_;
        return unless $module eq 'unicore/lib/gc_sc/IdContin.pl';

        # Open the file wherever it exists.
        my $file;
        for my $dir (@INC) {
            my $tst = "$dir/$module";
            next unless -f $tst;
            $file = $tst;
        }

        # Slurp the entire file.
        open my $fh, '<', $file
            or die "Can't open $file: $!";
        my @contents = readline $fh;
        close $fh;

        # Find out where the hex region starts.
        my $start_ix;
        for ( 0 .. $#contents ) {
            next unless $contents[$_] =~ /^[\dA-F]+(?:\s+[\dA-F]+\s*)?
+$/;
            $start_ix = $_;
            last;
        }

        # Find out where to insert my 2203/2005 codes.
        for ( $start_ix .. $#contents ) {
            my @chars = map hex("0x$_"), $contents[$_] =~ /(\S+)/g
                or last;
            my $char = $chars[-1];
            next if $char <= 0x2203;

            # Insert my two codes.
            splice @contents, $_, 0, "2203\t2204\n";
            last;
        }

        # Return the modified file.
        return (
            sub {
                if (@contents) {
                    $_ = shift @contents;
                    return 1;
                }
                else {
                    return 0;
                }
            }
        );
    };
}

[download]
use utf8;
use strict;
use warnings;
use Test::More tests => 2;
my @numbers = 1 .. 10;

# This works (but not normally)
BEGIN { like( "\x{2203}", qr/\p{IdContinue}/, "\N{THERE EXISTS} is an 
+identifier" ) }

# This doesn't.

[download]
sub ∃ (&\@) { my $predicate = shift @_; $predicate->() and return 1 for @_; 0 }

ok( ∃ { /\d/ } @numbers, '∃' );

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In reply to Mutable unicode character tables by diotalevi

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