my $string = " a 1 # ";
my $i = 0;
while () {
    if ( $string =~ /^\G\s+/gc ) {
        print "whitespace\n";
    }
    elsif ( $string =~ /^\G[0-9]+/gc ) {
        print "integer\n";
    }
    elsif ( $string =~ /^\G\w+/gc ) {
        print "word\n";
    }
    else {
        print "done\n";
        last;
    }
}

##</code><code>##

desired output:
whitespace
word
whitespace
integer
whitespace
done