<?php

/****
 * ASCIIMathPHP and associated classes:
 * -- XMLNode
 * -- MathMLNode extends XMLNode
 *
 * These classes are a PHP port of ASCIIMath
 * Version 1.3 Feb 19 2004, (c) Peter Jipsen http://www.chapman.edu/~jipsen
 *
 * ASCIIMathPHP Version 1.11, 26 April 2006, (c) Kee-Lin Steven Chan (kc56@cornell.edu)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License (at http://www.gnu.org/copyleft/gpl.html)
 * for more details.
 *
 * ChangeLog
 *
 * Ver 2.0
 * -- PHP5 only version of ASCIIMathPHP
 *
 * Ver 1.12.1
 * -- Included the missing setCurrExpr() method
 *
 * Ver 1.12
 * -- Added changes that David Lippman <DLippman@pierce.ctc.edu> made to bring ASCIIMathPHP up to
 * ASCIIMath 1.4.7 functionality.
 * -- Added parseIntExpr, for intermediate expression parsing rule, allowing x^2/x^3 to render as (x^2)/(x^3)
 * -- Added quotes as another way of designating text; "hello" is equivalent to text(hello)
 * -- Added FUNC designator to allow sin, cos, etc to act as functions, so sin(x)/x renders as {sin(x)}/x
 *
 * Ver 1.11
 * -- Fixed bug that stopped script execution for incomplete expressions
 * -- Changed the algorithm for parsing expressions so that it matches the longest string possible (greedy)
 *
 * Ver 1.10
 * -- Added definition support
 * -- Added stackrel support
 * -- Added a bunch of different symbols etc. >>, << and definitions like dx, dy, dz etc.
 *
 * Ver 1.02
 * -- Fixed bug with mbox and text
 * -- Fixed spacing bug with mbox and text
 *
 * Ver 1.01
 * -- Fixed Bug that did not parse symbols greater than a single character
 * correctly when appearing at end of expression.
 *
 ***/

class XMLNode
{
    // Private variables
    var $_id;
    var $_name;
    var $_content;
    var $_mt_elem_flg;
    var $_attr_arr;
    var $_child_arr;
    var $_nmspc;
    var $_nmspc_alias;
    var $_parent_id;
    var $_parent_node;

    function XMLNode($id = NULL)
    {
        $this->_id = isset($id) ? $id : md5(uniqid(rand(),1));
        $this->_name = '';
        $this->_content = '';
        $this->_mt_elem_flg = FALSE;
        $this->_attr_arr = array();
        $this->_child_arr = array();
        $this->_nmspc = '';
        $this->_nmspc_alias = '';
        $this->_parent_id = FALSE;
        $this->_parent_node = NULL;
    }

    function addChild(&$node)
    {
        $this->_child_arr[$node->getId()] = $node;
        $node->setParentId($this->_id);
        $node->setParentNode($this);
    }

    function addChildArr(&$node_arr)
    {
        $key_arr = array_keys($node_arr);
        $num_key = count($key_arr);

        for ($i = 0; $i < $num_key; $i++) {
            $node = $node_arr[$key_arr[$i]];
            $this->addChild($node);
        }
    }

    function insertChildBefore($idx,&$node)
    {
        $key_arr = array_keys($this->_child_arr);
        $num_key = count($key_arr);
        $tmp_arr = arry();

        for ($i = 0;$i < $num_key;$i++) {
            if ($i == $idx) {
                $tmp_arr[$node->getId()] = $node;
            }
            $tmp_arr[$key_arr[$i]] = $this->_child_arr[$key_arr[$i]];
        }
        $this->_child_arr = $tmp_arr;
    }

    function insertChildAfter($idx,&$node)
    {
        $key_arr = array_keys($this->_child_arr);
        $num_key = count($key_arr);
        $tmp_arr = arry();

        for ($i = 0;$i < $num_key;$i++) {
            $tmp_arr[$key_arr[$i]] = $this->_child_arr[$key_arr[$i]];
            if ($i == $idx) {
                $tmp_arr[$node->getId()] = $node;
            }
        }
        $this->_child_arr = $tmp_arr;
    }

    function setId($id)
    {
        $this->_id = $id;
    }

    function setName($name)
    {
        $this->_name = $name;
    }

    function setNamepace($nmspc)
    {
        $this->_nmspc = $nmspc;
    }

    function setNamespaceAlias($nmspc_alias)
    {
        $this->_nmspc_alias = $nmspc_alias;
    }

    function setContent($content)
    {
        $this->_content = $content;
    }

    function setEmptyElem($mt_elem_flg)
    {
        $this->_mt_elem_flg = $mt_elem_flg;
    }

    function setAttr($attr_nm,$attr_val)
    {
        $this->_attr_arr[$attr_nm] = $attr_val;
    }

    function setAttrArr($attr_arr)
    {
        $this->_attr_arr = $attr_arr;
    }

    function setParentId($id)
    {
        $this->_parent_id = $id;
    }

    function setParentNode(&$node)
    {
        $this->_parent_node = $node;
    }

    function getId()
    {
        return($this->_id);
    }

    function getName()
    {
        return($this->_name);
    }

    function getNamespace()
    {
        return($this->_nmspc);
    }

    function getNamespaceAlias()
    {
        return($this->_nmspc_alias);
    }

    function getContent()
    {
        return($this->_content);
    }

    function getAttr($attr_nm)
    {
        if (isset($this->_attr_arr[$attr_nm])) {
            return($this->_attr_arr[$attr_nm]);
        } else {
            return(NULL);
        }
    }

    function getAttrArr()
    {
        return($this->_attr_arr);
    }

    function getParentId()
    {
        return($this->parent_id);
    }

    function getParentNode()
    {
        return($this->_parent_node);
    }

    function getChild($id)
    {
        if (isset($this->_child_arr[$id])) {
            return($this->_child_arr[$id]);
        } else {
            return(FALSE);
        }
    }

    function getFirstChild()
    {
        $id_arr = array_keys($this->_child_arr);
        $num_child = count($id_arr);

        if ($num_child > 0) {
            return($this->_child_arr[$id_arr[0]]);
        } else {
            return(FALSE);
        }
    }

    function getLastChild()
    {
        $id_arr = array_keys($this->_child_arr);
        $num_child = count($id_arr);

        if ($num_child > 0) {
            return($this->_child_arr[$id_arr[$num_child - 1]]);
        } else {
            return(FALSE);
        }
    }

    function getChildByIdx($idx)
    {
        $id_arr = array_keys($this->_child_arr);

        if (isset($this->_child_arr[$id_arr[$idx]])) {
            return($this->_child_arr[$id_arr[$idx]]);
        } else {
            return(FALSE);
        }
    }

    function getNumChild()
    {
        return(count($this->_child_arr));
    }

    function removeChild($id)
    {
        unset($this->_child_arr[$id]);
    }

    function removeChildByIdx($idx)
    {
        $key_arr = array_keys($this->_child_arr);
        unset($this->_child_arr[$key_arr[$idx]]);
    }

    function removeFirstChild()
    {
        $key_arr = array_keys($this->_child_arr);
        unset($this->_child_arr[$key_arr[0]]);
    }

    function removeLastChild()
    {
        $key_arr = array_keys($this->_child_arr);
        unset($this->_child_arr[$key_arr[count($key_arr)-1]]);
    }

    function dumpXML($indent_str = "\t")
    {
        $attr_txt = $this->_dumpAttr();
        $name = $this->_dumpName();
        $xmlns = $this->_dumpXmlns();
        $lvl = $this->_getCurrentLevel();
        $indent = str_pad('',$lvl,$indent_str);

        if ($this->_mt_elem_flg) {
            $tag = "$indent<$name$xmlns$attr_txt />";
            return($tag);
        } else {
            $key_arr = array_keys($this->_child_arr);
            $num_child = count($key_arr);

            $tag = "$indent<$name$xmlns$attr_txt>$this->_content";

            for ($i = 0;$i < $num_child;$i++) {
                $node = $this->_child_arr[$key_arr[$i]];

                $child_txt = $node->dumpXML($indent_str);
                $tag .= "\n$child_txt";
            }

            $tag .= ($num_child > 0 ? "\n$indent</$name>" : "</$name>");
            return($tag);
        }
    }

    function _dumpAttr()
    {
        $id_arr = array_keys($this->_attr_arr);
        $id_arr_cnt = count($id_arr);
        $attr_txt = '';

        for($i = 0;$i < $id_arr_cnt;$i++) {
            $key = $id_arr[$i];
            $attr_txt .= " $key=\"{$this->_attr_arr[$key]}\"";
        }

        return($attr_txt);
    }

    function _dumpName()
    {
        $alias = $this->getNamespaceAlias();
        if ($alias == '') {
            return($this->getName());
        } else {
            return("$alias:" . $this->getName());
        }
    }

    function _dumpXmlns()
    {
        $nmspc = $this->getNamespace();
        $alias = $this->getNamespaceAlias();

        if ($nmspc != '') {
            if ($alias == '') {
                return(" xmlns=\"" . $nmspc . "\"");
            } else {
                return(" xmlns:$alias=\"" . $nmspc . "\"");
            }
        } else {
            return('');
        }
    }

    function _getCurrentLevel()
    {
        if ($this->_parent_id === FALSE) {
            return(0);
        } else {
            $node = $this->getParentNode();
            $lvl = $node->_getCurrentLevel();
            $lvl++;
            return($lvl);
        }
    }
}

class MathMLNode extends XMLNode
{
    function MathMLNode($id = NULL)
    {
        parent::XMLNode($id);
    }

    function removeBrackets()
    {
        if ($this->_name == 'mrow') {
            if ($c_node_0 = $this->getFirstChild()) {
                $c_node_0->isLeftBracket() ? $this->removeFirstChild() : 0;
            }

            if ($c_node_0 = $this->getLastChild()) {
                $c_node_0->isRightBracket() ? $this->removeLastChild() : 0;
            }
        }
    }

    function isLeftBracket()
    {
        switch ($this->_content) {
            case '{':
            case '[':
            case '(':
                return(TRUE);
                break;
        }
        return(FALSE);
    }

    function isRightBracket()
    {
        switch ($this->_content) {
            case '}':
            case ']':
            case ')':
                return(TRUE);
                break;
        }
        return(FALSE);
    }
}

class ASCIIMathPHP
{
    var $_expr;
    var $_curr_expr;
    var $_prev_expr;
    var $_symbol_arr;
    var $_node_arr;
    var $_node_cntr;

    function ASCIIMathPHP($symbol_arr,$expr = NULL)
    {
        $this->_symbol_arr = $symbol_arr;
        if (isset($expr)) {
            $this->setExpr($expr);
        }
    }

    /**
     * Returns an empty node (containing a non-breaking space) 26-Apr-2006
     *
     * Used when an expression is incomplete
     *
     * @return object
     *
     * @access private
     */
    function emptyNode()
    {
        $tmp_node = $this->createNode();
        $tmp_node->setName('mn');
        $tmp_node->setContent('&#' . hexdec('200B') . ';');
        return $tmp_node;
    }

    function pushExpr($prefix) // 2005-06-11 wes
    {
        $this->_curr_expr = $prefix . $this->_curr_expr;
    }

    function setExpr($expr)
    {
        $this->_expr = $expr;
        $this->_curr_expr = $expr;
        $this->_prev_expr = $expr;

        $this->_node_arr = array();
        $this->_node_cntr = 0;
    }

    function genMathML($attr_arr = NULL)
    {
        // <math> node
        $node_0 = $this->createNode();
        $node_0->setName('math');
        $node_0->setNamepace('http://www.w3.org/1998/Math/MathML');

        // <mstyle> node
        if (isset($attr_arr)) {
            $node_1 = $this->createNode();
            $node_1->setName('mstyle');
            $node_1->setAttrArr($attr_arr);

            $node_arr = $this->parseExpr();

            $node_1->addChildArr($node_arr);
            $node_0->addChild($node_1);
        } else {
            $node_arr = $this->parseExpr();
            $node_0->addChildArr($node_arr);
        }

        return TRUE;
    }

    /*
    function  mergeNodeArr(&$node_arr_0,&$node_arr_1)
    {
        $key_arr_0 = array_keys($node_arr_0);
        $key_arr_1 = array_keys($node_arr_1);

        $num_key_0 = count($key_arr_0);
        $num_key_1 = count($key_arr_1);

        $merge_arr = array();

        for ($i = 0;$i < $num_key_0;$i++) {
            $merge_arr[$key_arr_0[$i]] = $node_arr_0[$key_arr_0[$i]];
        }

        for ($j = 0;$j < $num_key_1;$i++) {
            $merge_arr[$key_arr_1[$i]] = $node_arr_1[$key_arr_1[$i]];
        }

        return($merge_arr);
    }
    */

    //Broken out of parseExpr Sept 7, 2006 David Lippman for
    //ASCIIMathML 1.4.7 compatibility
    function  parseIntExpr()
    {
        $sym_0 = $this->getSymbol();
        $node_0 = $this->parseSmplExpr();
        $sym = $this->getSymbol();

        if (isset($sym['infix']) && $sym['input'] != '/') {
            $this->chopExpr($sym['symlen']);
            $node_1 = $this->parseSmplExpr();

            if ($node_1 === FALSE) { //show box in place of missing argument
                $node_1 = $this->emptyNode();//??
            } else {
                $node_1->removeBrackets();
            }

            // If 'sub' -- subscript
            if ($sym['input'] == '_') {

                $sym_1 = $this->getSymbol();

                // If 'sup' -- superscript
                if ($sym_1['input'] == '^') {
                    $this->chopExpr($sym_1['symlen']);
                    $node_2 = $this->parseSmplExpr();
                    $node_2->removeBrackets();

                    $node_3 = $this->createNode();
                    $node_3->setName(isset($sym_0['underover']) ? 'munderover' : 'msubsup');
                    $node_3->addChild($node_0);
                    $node_3->addChild($node_1);
                    $node_3->addChild($node_2);

                    $node_4 = $this->createNode();
                    $node_4->setName('mrow');
                    $node_4->addChild($node_3);

                    return $node_4;
                } else {
                    $node_2 = $this->createNode();
                    $node_2->setName(isset($sym_0['underover']) ? 'munder' : 'msub');
                    $node_2->addChild($node_0);
                    $node_2->addChild($node_1);

                    return $node_2;
                }
            } else {
                $node_2 = $this->createNode();
                $node_2->setName($sym['tag']);
                $node_2->addChild($node_0);
                $node_2->addChild($node_1);

                return($node_2);
            }
        } elseif ($node_0 !== FALSE) {
            return($node_0);
        } else {
            return $this->emptyNode();
        }

    }

    function  parseExpr()
    {
        // Child/Fragment array
        $node_arr = array();

        // Deal whole expressions like 'ax + by + c = 0' etc.
        do {
            $sym_0 = $this->getSymbol();
            $node_0 = $this->parseIntExpr();
            $sym = $this->getSymbol();
            // var_dump($sym);

            if (isset($sym['infix']) && $sym['input'] == '/') {
                $this->chopExpr($sym['symlen']);
                $node_1 = $this->parseIntExpr();

                if ($node_1 === FALSE) { //should show box in place of missing argument
                    $node_1 = $this->emptyNode();
                    continue;
                }

                $node_1->removeBrackets();

                // If 'div' -- divide
                $node_0->removeBrackets();
                $node_2 = $this->createNode();
                $node_2->setName($sym['tag']);
                $node_2->addChild($node_0);
                $node_2->addChild($node_1);
                $node_arr[$node_2->getId()] = $node_2;

            } elseif ($node_0 !== FALSE) {
                $node_arr[$node_0->getId()] = $node_0;
            }
        } while (!isset($sym['right_bracket']) && $sym !== FALSE && $sym['output'] != '');

        //var_dump($sym);
        // Possibly to deal with matrices
        if (isset($sym['right_bracket'])) {
            $node_cnt = count($node_arr);
            $key_node_arr = array_keys($node_arr);

            if ($node_cnt > 1) {
                $node_5 = $node_arr[$key_node_arr[$node_cnt-1]];
                $node_6 = $node_arr[$key_node_arr[$node_cnt-2]];
            } else {
                $node_5 = FALSE;
                $node_6 = FALSE;
            }

            // Dealing with matrices
            if ($node_5 !== FALSE && $node_6 !== FALSE &&
                $node_cnt > 1 &&
                $node_5->getName() == 'mrow' &&
                $node_6->getName() == 'mo' &&
                $node_6->getContent() == ',') {

                // Checking if Node 5 has a LastChild
                if ($node_7 = $node_5->getLastChild()) {
                    $node_7_cntnt = $node_7->getContent();
                } else {
                    $node_7_cntnt = FALSE;
                }

                // If there is a right bracket
                if ($node_7 !== FALSE && ($node_7_cntnt == ']' || $node_7_cntnt == ')')) {

                    // Checking if Node 5 has a firstChild
                    if ($node_8 = $node_5->getFirstChild()) {
                        $node_8_cntnt = $node_8->getContent();
                    } else {
                        $node_8_cntnt = FALSE;
                    }

                    // If there is a matching left bracket
                    if ($node_8 !== FALSE &&
                        (($node_8_cntnt == '(' && $node_7_cntnt == ')' && $sym['output'] != '}') ||
                        ($node_8_cntnt == '[' && $node_7_cntnt == ']'))) {

                        $is_mtrx_flg = TRUE;
                        $comma_pos_arr = array();

                        $i = 0;

                        while ($i < $node_cnt && $is_mtrx_flg) {
                            $tmp_node = $node_arr[$key_node_arr[$i]];

                            if($tmp_node_first = $tmp_node->getFirstChild()) {
                                $tnfc = $tmp_node_first->getContent();
                            } else {
                                $tnfc = FALSE;
                            }

                            if($tmp_node_last = $tmp_node->getLastChild()) {
                                $tnlc = $tmp_node_last->getContent();
                            } else {
                                $tnlc = FALSE;
                            }

                            if (isset($key_node_arr[$i+1])) {
                                $next_tmp_node = $node_arr[$key_node_arr[$i+1]];
                                $ntnn = $next_tmp_node->getName();
                                $ntnc = $next_tmp_node->getContent();
                            } else {
                                $ntnn = FALSE;
                                $ntnc = FALSE;
                            }

                            // Checking each node in node array for matrix criteria
                            if ($is_mtrx_flg) {
                                $is_mtrx_flg = $tmp_node->getName() == 'mrow' &&
                                    ($i == $node_cnt-1 || $ntnn == 'mo' && $ntnc == ',') &&
                                    $tnfc == $node_8_cntnt && $tnlc == $node_7_cntnt;
                            }

                            if ($is_mtrx_flg) {
                                for ($j = 0;$j < $tmp_node->getNumChild();$j++) {
                                    $tmp_c_node = $tmp_node->getChildByIdx($j);

                                    if ($tmp_c_node->getContent() == ',') {
                                        $comma_pos_arr[$i][] = $j;
                                    }
                                }
                            }

                            if ($is_mtrx_flg && $i > 1) {

                                $cnt_cpan = isset($comma_pos_arr[$i]) ? count($comma_pos_arr[$i]) : NULL;
                                $cnt_cpap = isset($comma_pos_arr[$i-2]) ? count($comma_pos_arr[$i-2]) : NULL;
                                $is_mtrx_flg = $cnt_cpan == $cnt_cpap;
                            }

                            $i += 2;
                        }

                        // If the node passes the matrix tests
                        if ($is_mtrx_flg) {
                            $tab_node_arr = array();

                            for ($i = 0;$i < $node_cnt;$i += 2) {
                                $tmp_key_node_arr = array_keys($node_arr);
                                if (!($tmp_node = $node_arr[$tmp_key_node_arr[0]])) {
                                    break;
                                }
                                $num_child = $tmp_node->getNumChild();
                                $k = 0;

                                $tmp_node->removeFirstChild();

                                $row_node_arr = array();
                                $row_frag_node_arr = array();

                                for ($j = 1;$j < ($num_child-1);$j++) {
                                    if (isset($comma_pos_arr[$i][$k]) &&
                                        $j == $comma_pos_arr[$i][$k]) {

                                        $tmp_node->removeFirstChild();

                                        $tmp_c_node = $this->createNode();
                                        $tmp_c_node->setName('mtd');
                                        $tmp_c_node->addChildArr($row_frag_node_arr);
                                        $row_frag_node_arr = array();

                                        $row_node_arr[$tmp_c_node->getId()] = $tmp_c_node;

                                        $k++;
                                    } else {

                                        if ($tmp_c_node = $tmp_node->getFirstChild()) {
                                            $row_frag_node_arr[$tmp_c_node->getId()] = $tmp_c_node;
                                            $tmp_node->removeFirstChild();
                                        }
                                    }
                                }

                                $tmp_c_node = $this->createNode();
                                $tmp_c_node->setName('mtd');
                                $tmp_c_node->addChildArr($row_frag_node_arr);

                                $row_node_arr[$tmp_c_node->getId()] = $tmp_c_node;

                                if (count($node_arr) > 2) {
                                    $tmp_key_node_arr = array_keys($node_arr);
                                    unset($node_arr[$tmp_key_node_arr[0]]);
                                    unset($node_arr[$tmp_key_node_arr[1]]);
                                }

                                $tmp_c_node = $this->createNode();
                                $tmp_c_node->setName('mtr');
                                $tmp_c_node->addChildArr($row_node_arr);

                                $tab_node_arr[$tmp_c_node->getId()] = $tmp_c_node;
                            }

                            $tmp_c_node = $this->createNode();
                            $tmp_c_node->setName('mtable');
                            $tmp_c_node->addChildArr($tab_node_arr);

                            if (isset($sym['invisible'])) {
                                $tmp_c_node->setAttr('columnalign','left');
                            }

                            $key_node_arr = array_keys($node_arr);
                            $tmp_c_node->setId($key_node_arr[0]);

                            $node_arr[$tmp_c_node->getId()] = $tmp_c_node;
                        }
                    }
                }
            }

            $this->chopExpr($sym['symlen']);
            if (!isset($sym['invisible'])) {
                $node_7 = $this->createNode();
                $node_7->setName('mo');
                $node_7->setContent($sym['output']);
                $node_arr[$node_7->getId()] = $node_7;
            }
        }

        return($node_arr);
    }

    function  parseSmplExpr()
    {
        $sym = $this->getSymbol();

        if (!$sym || isset($sym['right_bracket'])) //return FALSE;
            return $this->emptyNode();

        $this->chopExpr($sym['symlen']);

        // 2005-06-11 wes: add definition type support
        if(isset($sym['definition'])) {
            $this->pushExpr($sym['output']);
            $sym = $this->getSymbol();
            $this->chopExpr($sym['symlen']);
        }

        if (isset($sym['left_bracket'])) {
            $node_arr = $this->parseExpr();

            if (isset($sym['invisible'])) {
                $node_0 = $this->createNode();
                $node_0->setName('mrow');
                $node_0->addChildArr($node_arr);

                return($node_0);
            } else {
                $node_0 = $this->createNode();
                $node_0->setName('mo');
                $node_0->setContent($sym['output']);

                $node_1 = $this->createNode();
                $node_1->setName('mrow');
                $node_1->addChild($node_0);
                $node_1->addChildArr($node_arr);

                return($node_1);
            }
        } elseif (isset($sym['unary'])) {

            if ($sym['input'] == 'sqrt') {
                $node_0 = $this->parseSmplExpr();
                $node_0->removeBrackets();

                $node_1 = $this->createNode();
                $node_1->setName($sym['tag']);
                $node_1->addChild($node_0);

                return($node_1);
            } elseif (isset($sym['func'])) { //added 2006-9-7 David Lippman
                $expr = ltrim($this->getCurrExpr());
                $st = $expr{0};
                $node_0 = $this->parseSmplExpr();
                //$node_0->removeBrackets();
                if ($st=='^' || $st == '_' || $st=='/' || $st=='|' || $st==',') {
                    $node_1 = $this->createNode();
                    $node_1->setName($sym['tag']);
                    $node_1->setContent($sym['output']);
                    $this->setCurrExpr($expr);
                    return($node_1);
                } else {
                    $node_1 = $this->createNode();
                    $node_1->setName('mrow');
                    $node_2 = $this->createNode();
                    $node_2->setName($sym['tag']);
                    $node_2->setContent($sym['output']);
                    $node_1->addChild($node_2);
                    $node_1->addChild($node_0);
                    return($node_1);
                }
            } elseif ($sym['input'] == 'text' || $sym['input'] == 'mbox' || $sym['input'] == '"') {
                $expr = ltrim($this->getCurrExpr());
                if ($sym['input']=='"') {
                    $end_brckt = '"';
                    $txt = substr($expr,0,strpos($expr,$end_brckt));
                } else {
                    switch($expr{0}) {
                        case '(':
                            $end_brckt = ')';
                            break;
                        case '[':
                            $end_brckt = ']';
                            break;
                        case '{':
                            $end_brckt = '}';
                            break;
                        default:
                            $end_brckt = chr(11); // A character that will never be matched.
                            break;
                    }
                    $txt = substr($expr,1,strpos($expr,$end_brckt)-1);
                }

                //$txt = substr($expr,1,strpos($expr,$end_brckt)-1);
                $len = strlen($txt);

                $node_0 = $this->createNode();
                $node_0->setName('mrow');

                if ($len > 0) {
                    if ($txt{0} == " ") {
                        $node_1 = $this->createNode();
                        $node_1->setName('mspace');
                        $node_1->setAttr('width','1ex');

                        $node_0->addChild($node_1);
                    }

                    $node_3 = $this->createNode();
                    $node_3->setName($sym['tag']);
                    $node_3->setContent(trim($txt));

                    $node_0->addChild($node_3);

                    if ($len > 1 && $txt{$len-1} == " ") {
                        $node_2 = $this->createNode();
                        $node_2->setName('mspace');
                        $node_2->setAttr('width','1ex');

                        $node_0->addChild($node_2);
                    }

                    $this->chopExpr($len+2);
                }
                return($node_0);

            } elseif (isset($sym['acc'])) {
                $node_0 = $this->parseSmplExpr();
                $node_0->removeBrackets();

                $node_1 = $this->createNode();
                $node_1->setName($sym['tag']);
                $node_1->addChild($node_0);

                $node_2 = $this->createNode();
                $node_2->setName('mo');
                $node_2->setContent($sym['output']);

                $node_1->addChild($node_2);
                return($node_1);
            } else {
                // Font change commands -- to complete
            }
        } elseif (isset($sym['binary'])) {
            $node_arr = array();

            $node_0 = $this->parseSmplExpr();
            $node_0->removeBrackets();

            $node_1 = $this->parseSmplExpr();
            $node_1->removeBrackets();

            /* 2005-06-05 wes: added stackrel */
            if ($sym['input'] == 'root' || $sym['input'] == 'stackrel') {
                $node_arr[$node_1->getId()] = $node_1;
                $node_arr[$node_0->getId()] = $node_0;
            } elseif ($sym['input'] == 'frac') {
                $node_arr[$node_0->getId()] = $node_0;
                $node_arr[$node_1->getId()] = $node_1;
            }

            $node_2 = $this->createNode();
            $node_2->setName($sym['tag']);
            $node_2->addChildArr($node_arr);

            return($node_2);
        } elseif (isset($sym['infix'])) {
            $node_0 = $this->createNode();
            $node_0->setName('mo');
            $node_0->setContent($sym['output']);

            return($node_0);
        } elseif (isset($sym['space'])) {
            $node_0 = $this->createNode();
            $node_0->setName('mrow');

            $node_1 = $this->createNode();
            $node_1->setName('mspace');
            $node_1->setAttr('width',$sym['space']);

            $node_2 = $this->createNode();
            $node_2->setName($sym['tag']);
            $node_2->setContent($sym['output']);

            $node_3 = $this->createNode();
            $node_3->setName('mspace');
            $node_3->setAttr('width',$sym['space']);

            $node_0->addChild($node_1);
            $node_0->addChild($node_2);
            $node_0->addChild($node_3);

            return($node_0);
        } else {

            // A constant
            $node_0 = $this->createNode();
            $node_0->setName($sym['tag']);
            $node_0->setContent($sym['output']);
            return($node_0);
        }

        // Return an empty node
        return $this->emptyNode();
    }

    function getMathML()
    {
        $root = $this->_node_arr[0];
        return($root->dumpXML());
    }

    function getCurrExpr()
    {
        return($this->_curr_expr);
    }

    function setCurrExpr($str)
    {
        $this->_curr_expr = $str;
    }

    function getExpr()
    {
        return($this->_expr);
    }

    function getPrevExpr()
    {
        return($this->_prev_expr);
    }

    function  createNode()
    {
        $node = new MathMLNode($this->_node_cntr);
        // $node->setNamespaceAlias('m');
        $this->_node_arr[$this->_node_cntr] = $node;
        $this->_node_cntr++;
        return($node);
    }

    /**
     * Gets the largest symbol in the expression (greedy). Changed from non-greedy 26-Apr-2006
     *
     * @parameter boolean[optional] Chop original string?
     *
     * @return mixed
     *
     * @access private
     */
    function getSymbol($chop_flg = FALSE)
    {
        // Implemented a reverse symbol matcher.
        // Instead of going front to back, it goes back to front. Steven 26-Apr-2006
        $chr_cnt = strlen($this->_curr_expr);

        if ($chr_cnt == 0) return FALSE;

        for ($i = $chr_cnt; $i > 0; $i--) {
            $sym_0 = substr($this->_curr_expr,0,$i);

            // Reading string for numeric values
            if (is_numeric($sym_0)) {

                if ($chop_flg) $this->chopExpr($i);
                return array('input'=>$sym_0, 'tag'=>'mn', 'output'=>$sym_0, 'symlen'=>$i);

            } elseif (isset($this->_symbol_arr[$sym_0])) {

                if ($chop_flg) $this->chopExpr($i);
                $sym_arr = $this->_symbol_arr[$sym_0];
                $sym_arr['symlen'] = $i;
                return $sym_arr;
            }
        }

        // Reading string for alphabetic constants and the minus sign
        $char = $this->_curr_expr{0};
        $len_left = $chop_flg ? $this->chopExpr(1) : strlen($this->_curr_expr)-1;

        // Deals with expressions of length 1
        if ($len_left == 0 && isset($this->_symbol_arr[$char])) {
            $sym_arr = $this->_symbol_arr[$char];
            $sym_arr['symlen'] = 1;
            return $sym_arr;
        } else {
            $tag = preg_match('/[a-z]/i',$char) ? 'mi' : 'mo';
            return array('input'=>$char, 'tag'=>$tag, 'output'=>$char, 'symlen'=>1);
        }
    }

    function chopExpr($strlen)
    {
        $this->_prev_expr = $this->_curr_expr;

        if ($strlen == strlen($this->_curr_expr)) {
            $this->_curr_expr = '';
            return(0);
        } else {
            $this->_curr_expr = ltrim(substr($this->_curr_expr,$strlen));
            return(strlen($this->_curr_expr));
        }
    }
}