function quote( $value ) {

        $value = $this->format( $value );

        if ( $value === null ) {

            return "NULL";

        }

        if ( $value === false ) {

            return "'0'";

        }

        if ( $value === true ) {

            return "'1'";

        }

        if ( is_int( $value ) ) {

            return "'" . ( (string) $value ) . "'";

        }

        if ( is_float( $value ) ) {

            return "'" . sprintf( "%F", $value ) . "'";

        }

        if ( $value instanceof Literal ) {

            return $value->value;

        }

        return $this->pdo->quote( $value );

    }