I had a version using s/^PATTERN// as well, but for some reason, I thought that using /\GPATTERN/gc looked cuter.

BTW, this is a recursive descent parser.

use Data::Dumper;
print Dumper parse_lpc_expr(
q#({ 1, 2, "three", 0, ({ "internal", "array", 0, }),
  ([ ({"key1", "key2"}): "value", "key": "anothervalue" ]),
  ({ "arrays", ({ "even", ({ "nest"})})}), "end", })#);

# wrapper:
sub parse_lpc_expr {
    local $_ = shift;
    s/(?=[\015\012])\015?\012?/\n/g;
    parse_lpc_item();
}


# Actual parser starts here:
sub parse_lpc_item {
    my $result;
    /\G\s*/gc;
    pos() < length or return;
    if(/\G\(\{/gc) {
        $result = parse_lpc_array();
        /\G\s*\}\)/gc or error("})");
    } elsif (/\G\(\[/gc) {
        $result = parse_lpc_mapping();
        /\G\s*\]\)/gc or error("])");
    } elsif (/\G(-?(?:\d+\.?\d*|\.\d+))/gc) {
        $result = $1;
    } elsif (/\G("(?:[^"\n\\]|\\.|"\s*\")*")/sgc) {
        $result = $1;   # lazy
    } else {
        error();
    }
    return $result;
}

sub parse_lpc_array {
    my @result;
    while(length) {
        last if /\G(?=\}\))/gc;
        my($item) = parse_lpc_item() or last;
        push @result, $item;
        /\G\s*,\s*/gc or last;
    }
    return \@result;
}

sub parse_lpc_mapping {
    my %result;
    while(length) {
        last if /\G(?=\]\))/gc;
        my($key) = parse_lpc_item() or last;
        /\G\s*:\s*/gc or error(":");
        my($value) = parse_lpc_item() or error();
        if(ref $key eq 'ARRAY') {
            foreach(@$key) {
                die "A mapping should only have simple keys, or arrays
+ of simple keys\n" if ref;
                $result{$_} = $value ;
            }
        } elsif(ref $key) {
            die "A mapping can't have a mapping as a key\n";
        } else {
            $result{$key} = $value;
        }
        /\G\s*,\s*/gc or last;
    }
    return \%result;
}

sub error {
    my($expect) = @_;
    s/\G\s*(\S{0,5})/^$1/;
    if(defined $expect) {
        die "Expected \"$expect\", found \"$1\" at \"$_\"\n";
    } else {
        die "Can't parse \"$1\" at \"$_\"\n";
    }
}
[download]

$VAR1 = [
          '1',
          '2',
          '"three"',
          '0',
          [
            '"internal"',
            '"array"',
            '0'
          ],
          {
            '"key1"' => '"value"',
            '"key"' => '"anothervalue"',
            '"key2"' => '"value"'
          },
          [
            '"arrays"',
            [
              '"even"',
              [
                '"nest"'
              ]
            ]
          ],
          '"end"'
        ];
[download]