parser.php

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        } elseif ($this->_current_token == SPREADSHEET_EXCEL_WRITER_GE) {
            $this->_advance();
            $result2 = $this->_expression();
            if (PEAR::isError($result2)) {
                return $result2;
            }
            $result = $this->_createTree('ptgGE', $result, $result2);
        } elseif ($this->_current_token == SPREADSHEET_EXCEL_WRITER_EQ) {
            $this->_advance();
            $result2 = $this->_expression();
            if (PEAR::isError($result2)) {
                return $result2;
            }
            $result = $this->_createTree('ptgEQ', $result, $result2);
        } elseif ($this->_current_token == SPREADSHEET_EXCEL_WRITER_NE) {
            $this->_advance();
            $result2 = $this->_expression();
            if (PEAR::isError($result2)) {
                return $result2;
            }
            $result = $this->_createTree('ptgNE', $result, $result2);
        }
        return $result;
    }

    /**
    * It parses a expression. It assumes the following rule:
    * Expr -> Term [("+" | "-") Term]
    *      -> "string"
    *      -> "-" Term
    *
    * @access private
    * @return mixed The parsed ptg'd tree on success, PEAR_Error on failure
    */
    function _expression()
    {
        // If it's a string return a string node
        if (ereg("^\"[^\"]{0,255}\"$", $this->_current_token)) {
            $result = $this->_createTree($this->_current_token, '', '');
            $this->_advance();
            return $result;
        } elseif ($this->_current_token == SPREADSHEET_EXCEL_WRITER_SUB) {
            // catch "-" Term
            $this->_advance();
            $result2 = $this->_expression();
            $result = $this->_createTree('ptgUminus', $result2, '');
            return $result;
        }
        $result = $this->_term();
        if (PEAR::isError($result)) {
            return $result;
        }
        while (($this->_current_token == SPREADSHEET_EXCEL_WRITER_ADD) or
               ($this->_current_token == SPREADSHEET_EXCEL_WRITER_SUB)) {
        /**/
            if ($this->_current_token == SPREADSHEET_EXCEL_WRITER_ADD) {
                $this->_advance();
                $result2 = $this->_term();
                if (PEAR::isError($result2)) {
                    return $result2;
                }
                $result = $this->_createTree('ptgAdd', $result, $result2);
            } else {
                $this->_advance();
                $result2 = $this->_term();
                if (PEAR::isError($result2)) {
                    return $result2;
                }
                $result = $this->_createTree('ptgSub', $result, $result2);
            }
        }
        return $result;
    }

    /**
    * This function just introduces a ptgParen element in the tree, so that Excel
    * doesn't get confused when working with a parenthesized formula afterwards.
    *
    * @access private
    * @see _fact()
    * @return array The parsed ptg'd tree
    */
    function _parenthesizedExpression()
    {
        $result = $this->_createTree('ptgParen', $this->_expression(), '');
        return $result;
    }

    /**
    * It parses a term. It assumes the following rule:
    * Term -> Fact [("*" | "/") Fact]
    *
    * @access private
    * @return mixed The parsed ptg'd tree on success, PEAR_Error on failure
    */
    function _term()
    {
        $result = $this->_fact();
        if (PEAR::isError($result)) {
            return $result;
        }
        while (($this->_current_token == SPREADSHEET_EXCEL_WRITER_MUL) or
               ($this->_current_token == SPREADSHEET_EXCEL_WRITER_DIV)) {
        /**/
            if ($this->_current_token == SPREADSHEET_EXCEL_WRITER_MUL) {
                $this->_advance();
                $result2 = $this->_fact();
                if (PEAR::isError($result2)) {
                    return $result2;
                }
                $result = $this->_createTree('ptgMul', $result, $result2);
            } else {
                $this->_advance();
                $result2 = $this->_fact();
                if (PEAR::isError($result2)) {
                    return $result2;
                }
                $result = $this->_createTree('ptgDiv', $result, $result2);
            }
        }
        return $result;
    }

    /**
    * It parses a factor. It assumes the following rule:
    * Fact -> ( Expr )
    *       | CellRef
    *       | CellRange
    *       | Number
    *       | Function
    *
    * @access private
    * @return mixed The parsed ptg'd tree on success, PEAR_Error on failure
    */
    function _fact()
    {
        if ($this->_current_token == SPREADSHEET_EXCEL_WRITER_OPEN) {
            $this->_advance();         // eat the "("
            $result = $this->_parenthesizedExpression();
            if ($this->_current_token != SPREADSHEET_EXCEL_WRITER_CLOSE) {
                return $this->raiseError("')' token expected.");
            }
            $this->_advance();         // eat the ")"
            return $result;
        }
        // if it's a reference
        if (preg_match('/^\$?[A-Ia-i]?[A-Za-z]\$?[0-9]+$/',$this->_current_token))
        {
            $result = $this->_createTree($this->_current_token, '', '');
            $this->_advance();
            return $result;
        }
        // If it's an external reference (Sheet1!A1 or Sheet1:Sheet2!A1)
        elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z][0-9]+$/u",$this->_current_token))
        {
            $result = $this->_createTree($this->_current_token, '', '');
            $this->_advance();
            return $result;
        }
        // If it's an external reference ('Sheet1'!A1 or 'Sheet1:Sheet2'!A1)
        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z][0-9]+$/u",$this->_current_token))
        {
            $result = $this->_createTree($this->_current_token, '', '');
            $this->_advance();
            return $result;
        }
        // if it's a range
        elseif (preg_match("/^(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+:(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+$/",$this->_current_token) or 
                preg_match("/^(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+\.\.(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+$/",$this->_current_token))
        {
            $result = $this->_current_token;
            $this->_advance();
            return $result;
        }
        // If it's an external range (Sheet1!A1 or Sheet1!A1:B2)
        elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/u",$this->_current_token))
        {
            $result = $this->_current_token;
            $this->_advance();
            return $result;
        }
        // If it's an external range ('Sheet1'!A1 or 'Sheet1'!A1:B2)
        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/u",$this->_current_token))
        {
            $result = $this->_current_token;
            $this->_advance();
            return $result;
        }
        elseif (is_numeric($this->_current_token))
        {
            $result = $this->_createTree($this->_current_token, '', '');
            $this->_advance();
            return $result;
        }
        // if it's a function call
        elseif (eregi("^[A-Z0-9\xc0-\xdc\.]+$",$this->_current_token))
        {
            $result = $this->_func();
            return $result;
        }
        return $this->raiseError("Syntax error: ".$this->_current_token.
                                 ", lookahead: ".$this->_lookahead.
                                 ", current char: ".$this->_current_char);
    }

    /**
    * It parses a function call. It assumes the following rule:
    * Func -> ( Expr [,Expr]* )
    *
    * @access private
    * @return mixed The parsed ptg'd tree on success, PEAR_Error on failure
    */
    function _func()
    {
        $num_args = 0; // number of arguments received
        $function = strtoupper($this->_current_token);
        $result   = ''; // initialize result
        $this->_advance();
        $this->_advance();         // eat the "("
        while ($this->_current_token != ')') {
        /**/
            if ($num_args > 0) {
                if ($this->_current_token == SPREADSHEET_EXCEL_WRITER_COMA or
                    $this->_current_token == SPREADSHEET_EXCEL_WRITER_SEMICOLON)
                {
                    $this->_advance();  // eat the "," or ";"
                } else {
                    return $this->raiseError("Syntax error: comma expected in ".
                                      "function $function, arg #{$num_args}");
                }
                $result2 = $this->_condition();
                if (PEAR::isError($result2)) {
                    return $result2;
                }
                $result = $this->_createTree('arg', $result, $result2);
            } else { // first argument
                $result2 = $this->_condition();
                if (PEAR::isError($result2)) {
                    return $result2;
                }
                $result = $this->_createTree('arg', '', $result2);
            }
            $num_args++;
        }
        if (!isset($this->_functions[$function])) {
            return $this->raiseError("Function $function() doesn't exist");
        }
        $args = $this->_functions[$function][1];
        // If fixed number of args eg. TIME($i,$j,$k). Check that the number of args is valid.
        if (($args >= 0) and ($args != $num_args)) {
            return $this->raiseError("Incorrect number of arguments in function $function() ");
        }

        $result = $this->_createTree($function, $result, $num_args);
        $this->_advance();         // eat the ")"
        return $result;
    }

    /**
    * Creates a tree. In fact an array which may have one or two arrays (sub-trees)
    * as elements.
    *
    * @access private
    * @param mixed $value The value of this node.
    * @param mixed $left  The left array (sub-tree) or a final node.
    * @param mixed $right The right array (sub-tree) or a final node.
    * @return array A tree
    */
    function _createTree($value, $left, $right)
    {
        return array('value' => $value, 'left' => $left, 'right' => $right);
    }

    /**
    * Builds a string containing the tree in reverse polish notation (What you
    * would use in a HP calculator stack).
    * The following tree:
    *
    *    +
    *   / \
    *  2   3
    *
    * produces: "23+"
    *
    * The following tree:
    *
    *    +
    *   / \
    *  3   *
    *     / \
    *    6   A1
    *
    * produces: "36A1*+"
    *
    * In fact all operands, functions, references, etc... are written as ptg's
    *
    * @access public
    * @param array $tree The optional tree to convert.
    * @return string The tree in reverse polish notation
    */
    function toReversePolish($tree = array())
    {
        $polish = ""; // the string we are going to return
        if (empty($tree)) { // If it's the first call use _parse_tree
            $tree = $this->_parse_tree;
        }
        if (is_array($tree['left'])) {
            $converted_tree = $this->toReversePolish($tree['left']);
            if (PEAR::isError($converted_tree)) {
                return $converted_tree;
            }
            $polish .= $converted_tree;
        } elseif ($tree['left'] != '') { // It's a final node
            $converted_tree = $this->_convert($tree['left']);
            if (PEAR::isError($converted_tree)) {
                return $converted_tree;
            }
            $polish .= $converted_tree;
        }
        if (is_array($tree['right'])) {
            $converted_tree = $this->toReversePolish($tree['right']);
            if (PEAR::isError($converted_tree)) {
                return $converted_tree;
            }
            $polish .= $converted_tree;
        } elseif ($tree['right'] != '') { // It's a final node
            $converted_tree = $this->_convert($tree['right']);
            i