sub _Lexer {

    for( $input ) {
        if( @heredoc ) {
            /\A(.*?)\n$heredoc[0][0]/s or die "Unterminated heredoc";
            $strings[ $heredoc[0][1] ] = $1;
            shift @heredoc;
        }

        s/^\s*//;

        return ($1,$1) if s/^([;.])//;
        return ('IDENT',$1) if s/^(\w+)//;

        if( s/^<<(\w+)// ) {
            push @heredoc, [ $1, $id ];
            return ( 'HEREDOC', $id++ );
        }
    }

    return ('',undef);
}