/application/helpers/expressions/em_core_helper.php

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<?php
/**
 * LimeSurvey
 * Copyright (C) 2007-2011 The LimeSurvey Project Team / Carsten Schmitz
 * All rights reserved.
 * License: GNU/GPL License v2 or later, see LICENSE.php
 * LimeSurvey is free software. This version may have been modified pursuant
 * to the GNU General Public License, and as distributed it includes or
 * is derivative of works licensed under the GNU General Public License or
 * other free or open source software licenses.
 * See COPYRIGHT.php for copyright notices and details.
 *
 *	$Id$
 */
/**
 * Description of ExpressionManager
 * (1) Does safe evaluation of PHP expressions.  Only registered Functions, and known Variables are allowed.
 *   (a) Functions include any math, string processing, conditional, formatting, etc. functions
 * (2) This class replaces LimeSurvey's <= 1.91+  process of resolving strings that contain LimeReplacementFields
 *   (a) String is split by expressions (by curly braces, but safely supporting strings and escaped curly braces)
 *   (b) Expressions (things surrounded by curly braces) are evaluated - thereby doing LimeReplacementField substitution and/or more complex calculations
 *   (c) Non-expressions are left intact
 *   (d) The array of stringParts are re-joined to create the desired final string.
 * (3) The core of Expression Manager is a Recursive Descent Parser (RDP), based off of one build via JavaCC by TMSWhite in 1999.
 *   (a) Functions that start with RDP_ should not be touched unless you really understand compiler design.
 *
 * @author Thomas M. White (TMSWhite)
 */

class ExpressionManager {
    // These are the allowable suffixes for variables - each represents an attribute of a variable.
    static $RDP_regex_var_attr = 'code|gid|grelevance|gseq|jsName|mandatory|NAOK|qid|qseq|question|readWrite|relevanceStatus|relevance|rowdivid|sgqa|shown|type|valueNAOK|value';

    // These three variables are effectively static once constructed
    private $RDP_ExpressionRegex;
    private $RDP_TokenType;
    private $RDP_TokenizerRegex;
    private $RDP_CategorizeTokensRegex;
    private $RDP_ValidFunctions; // names and # params of valid functions

    // Thes variables are used while  processing the equation
    private $RDP_expr;  // the source expression
    private $RDP_tokens;    // the list of generated tokens
    private $RDP_count; // total number of $RDP_tokens
    private $RDP_pos;   // position within the $token array while processing equation
    private $RDP_errs;    // array of syntax errors
    private $RDP_onlyparse;
    private $RDP_stack; // stack of intermediate results
    private $RDP_result;    // final result of evaluating the expression;
    private $RDP_evalStatus;    // true if $RDP_result is a valid result, and  there are no serious errors
    private $varsUsed;  // list of variables referenced in the equation

    // These  variables are only used by sProcessStringContainingExpressions
    private $allVarsUsed;   // full list of variables used within the string, even if contains multiple expressions
    private $prettyPrintSource; // HTML formatted output of running sProcessStringContainingExpressions
    private $substitutionNum; // Keeps track of number of substitions performed XXX
    private $substitutionInfo; // array of JavaScripts to managing dynamic substitution
    private $jsExpression;  // caches computation of JavaScript equivalent for an Expression

    private $questionSeq;   // sequence order of question - so can detect if try to use variable before it is set
    private $groupSeq;  // sequence order of groups - so can detect if try to use variable before it is set
    private $surveyMode='group';

    // The following are only needed to enable click on variable names within pretty print and open new window to edit them
    private $sid=NULL; // the survey ID
    private $hyperlinkSyntaxHighlighting=true;  // TODO - change this back to false
    private $sgqaNaming=false;

    function __construct()
    {
        // List of token-matching regular expressions
        // Note, this is effectively a Lexer using Regular Expressions.  Don't change this unless you understand compiler design.
        $RDP_regex_dq_string = '(?<!\\\\)".*?(?<!\\\\)"';
        $RDP_regex_sq_string = '(?<!\\\\)\'.*?(?<!\\\\)\'';
        $RDP_regex_whitespace = '\s+';
        $RDP_regex_lparen = '\(';
        $RDP_regex_rparen = '\)';
        $RDP_regex_comma = ',';
        $RDP_regex_not = '!';
        $RDP_regex_inc_dec = '\+\+|--';
        $RDP_regex_binary = '[+*/-]';
        $RDP_regex_compare = '<=|<|>=|>|==|!=|\ble\b|\blt\b|\bge\b|\bgt\b|\beq\b|\bne\b';
        $RDP_regex_assign = '=';    // '=|\+=|-=|\*=|/=';
        $RDP_regex_sgqa = '(?:INSERTANS:)?[0-9]+X[0-9]+X[0-9]+[A-Z0-9_]*\#?[01]?(?:\.(?:' . ExpressionManager::$RDP_regex_var_attr . '))?';
        $RDP_regex_word = '(?:TOKEN:)?(?:[A-Z][A-Z0-9_]*)?(?:\.(?:[A-Z][A-Z0-9_]*))*(?:\.(?:' . ExpressionManager::$RDP_regex_var_attr . '))?';
        $RDP_regex_number = '[0-9]+\.?[0-9]*|\.[0-9]+';
        $RDP_regex_andor = '\band\b|\bor\b|&&|\|\|';
        $RDP_regex_lcb = '{';
        $RDP_regex_rcb = '}';
        $RDP_regex_sq = '\'';
        $RDP_regex_dq= '"';
        $RDP_regex_bs = '\\\\';

        $RDP_StringSplitRegex = array(
            $RDP_regex_lcb,
            $RDP_regex_rcb,
            $RDP_regex_sq,
            $RDP_regex_dq,
            $RDP_regex_bs,
        );

        // RDP_ExpressionRegex is the regular expression that splits apart strings that contain curly braces in order to find expressions
        $this->RDP_ExpressionRegex =  '#(' . implode('|',$RDP_StringSplitRegex) . ')#i';

        // asTokenRegex and RDP_TokenType must be kept in sync  (same number and order)
        $RDP_TokenRegex = array(
            $RDP_regex_dq_string,
            $RDP_regex_sq_string,
            $RDP_regex_whitespace,
            $RDP_regex_lparen,
            $RDP_regex_rparen,
            $RDP_regex_comma,
            $RDP_regex_andor,
            $RDP_regex_compare,
            $RDP_regex_sgqa,
            $RDP_regex_word,
            $RDP_regex_number,
            $RDP_regex_not,
            $RDP_regex_inc_dec,
            $RDP_regex_assign,
            $RDP_regex_binary,
            );

        $this->RDP_TokenType = array(
            'DQ_STRING',
            'SQ_STRING',
            'SPACE',
            'LP',
            'RP',
            'COMMA',
            'AND_OR',
            'COMPARE',
            'SGQA',
            'WORD',
            'NUMBER',
            'NOT',
            'OTHER',
            'ASSIGN',
            'BINARYOP',
           );

        // $RDP_TokenizerRegex - a single regex used to split and equation into tokens
        $this->RDP_TokenizerRegex = '#(' . implode('|',$RDP_TokenRegex) . ')#i';

        // $RDP_CategorizeTokensRegex - an array of patterns so can categorize the type of token found - would be nice if could get this from preg_split
        // Adding ability to capture 'OTHER' type, which indicates an error - unsupported syntax element
        $this->RDP_CategorizeTokensRegex = preg_replace("#^(.*)$#","#^$1$#i",$RDP_TokenRegex);
        $this->RDP_CategorizeTokensRegex[] = '/.+/';
        $this->RDP_TokenType[] = 'OTHER';

        // Each allowed function is a mapping from local name to external name + number of arguments
        // Functions can have a list of serveral allowable #s of arguments.
        // If the value is -1, the function must have a least one argument but can have an unlimited number of them
        // -2 means that at least one argument is required.  -3 means at least two arguments are required, etc.
        $this->RDP_ValidFunctions = array(
'abs' => array('abs', 'Math.abs', $this->gT('Absolute value'), 'number abs(number)', 'http://www.php.net/manual/en/function.checkdate.php', 1),
'acos' => array('acos', 'Math.acos', $this->gT('Arc cosine'), 'number acos(number)', 'http://www.php.net/manual/en/function.acos.php', 1),
'addslashes' => array('addslashes', $this->gT('addslashes'), 'Quote string with slashes', 'string addslashes(string)', 'http://www.php.net/manual/en/function.addslashes.php', 1),
'asin' => array('asin', 'Math.asin', $this->gT('Arc sine'), 'number asin(number)', 'http://www.php.net/manual/en/function.asin.php', 1),
'atan' => array('atan', 'Math.atan', $this->gT('Arc tangent'), 'number atan(number)', 'http://www.php.net/manual/en/function.atan.php', 1),
'atan2' => array('atan2', 'Math.atan2', $this->gT('Arc tangent of two variables'), 'number atan2(number, number)', 'http://www.php.net/manual/en/function.atan2.php', 2),
'ceil' => array('ceil', 'Math.ceil', $this->gT('Round fractions up'), 'number ceil(number)', 'http://www.php.net/manual/en/function.ceil.php', 1),
'checkdate' => array('checkdate', 'checkdate', $this->gT('Returns true(1) if it is a valid date in gregorian calendar'), 'bool checkdate(month,day,year)', 'http://www.php.net/manual/en/function.checkdate.php', 3),
'cos' => array('cos', 'Math.cos', $this->gT('Cosine'), 'number cos(number)', 'http://www.php.net/manual/en/function.cos.php', 1),
'count' => array('exprmgr_count', 'LEMcount', $this->gT('Count the number of answered questions in the list'), 'number count(arg1, arg2, ... argN)', '', -1),
'countif' => array('exprmgr_countif', 'LEMcountif', $this->gT('Count the number of answered questions in the list equal the first argument'), 'number countif(matches, arg1, arg2, ... argN)', '', -2),
'countifop' => array('exprmgr_countifop', 'LEMcountifop', $this->gT('Count the number of answered questions in the list which pass the critiera (arg op value)'), 'number countifop(op, value, arg1, arg2, ... argN)', '', -3),
'date' => array('date', 'date', $this->gT('Format a local date/time'), 'string date(format [, timestamp=time()])', 'http://www.php.net/manual/en/function.date.php', 1,2),
'exp' => array('exp', 'Math.exp', $this->gT('Calculates the exponent of e'), 'number exp(number)', 'http://www.php.net/manual/en/function.exp.php', 1),
'fixnum' => array('exprmgr_fixnum', 'LEMfixnum', $this->gT('Display numbers with comma as decimal separator, if needed'), 'string fixnum(number)', '', 1),
'floor' => array('floor', 'Math.floor', $this->gT('Round fractions down'), 'number floor(number)', 'http://www.php.net/manual/en/function.floor.php', 1),
'gmdate' => array('gmdate', 'gmdate', $this->gT('Format a GMT date/time'), 'string gmdate(format [, timestamp=time()])', 'http://www.php.net/manual/en/function.gmdate.php', 1,2),
'html_entity_decode' => array('html_entity_decode', 'html_entity_decode', $this->gT('Convert all HTML entities to their applicable characters (always uses ENT_QUOTES and UTF-8)'), 'string html_entity_decode(string)', 'http://www.php.net/manual/en/function.html-entity-decode.php', 1),
'htmlentities' => array('htmlentities', 'htmlentities', $this->gT('Convert all applicable characters to HTML entities (always uses ENT_QUOTES and UTF-8)'), 'string htmlentities(string)', 'http://www.php.net/manual/en/function.htmlentities.php', 1),
'htmlspecialchars' => array('expr_mgr_htmlspecialchars', 'htmlspecialchars', $this->gT('Convert special characters to HTML entities (always uses ENT_QUOTES and UTF-8)'), 'string htmlspecialchars(string)', 'http://www.php.net/manual/en/function.htmlspecialchars.php', 1),
'htmlspecialchars_decode' => array('expr_mgr_htmlspecialchars_decode', 'htmlspecialchars_decode', $this->gT('Convert special HTML entities back to characters (always uses ENT_QUOTES and UTF-8)'), 'string htmlspecialchars_decode(string)', 'http://www.php.net/manual/en/function.htmlspecialchars-decode.php', 1),
'idate' => array('idate', 'idate', $this->gT('Format a local time/date as integer'), 'string idate(string [, timestamp=time()])', 'http://www.php.net/manual/en/function.idate.php', 1,2),
'if' => array('exprmgr_if', 'LEMif', $this->gT('Conditional processing'), 'if(test,result_if_true,result_if_false)', '', 3),
'implode' => array('exprmgr_implode', 'LEMimplode', $this->gT('Join array elements with a string'), 'string implode(glue,arg1,arg2,...,argN)', 'http://www.php.net/manual/en/function.implode.php', -2),
'intval' => array('intval', 'LEMintval', $this->gT('Get the integer value of a variable'), 'int intval(number [, base=10])', 'http://www.php.net/manual/en/function.intval.php', 1,2),
'is_empty' => array('exprmgr_empty', 'LEMempty', $this->gT('Determine whether a variable is considered to be empty'), 'bool is_empty(var)', 'http://www.php.net/manual/en/function.empty.php', 1),
'is_float' => array('is_float', 'LEMis_float', $this->gT('Finds whether the type of a variable is float'), 'bool is_float(var)', 'http://www.php.net/manual/en/function.is-float.php', 1),
'is_int' => array('is_int', 'LEMis_int', $this->gT('Find whether the type of a variable is integer'), 'bool is_int(var)', 'http://www.php.net/manual/en/function.is-int.php', 1),
'is_nan' => array('is_nan', 'isNaN', $this->gT('Finds whether a value is not a number'), 'bool is_nan(var)', 'http://www.php.net/manual/en/function.is-nan.php', 1),
'is_null' => array('is_null', 'LEMis_null', $this->gT('Finds whether a variable is NULL'), 'bool is_null(var)', 'http://www.php.net/manual/en/function.is-null.php', 1),
'is_numeric' => array('is_numeric', 'LEMis_numeric', $this->gT('Finds whether a variable is a number or a numeric string'), 'bool is_numeric(var)', 'http://www.php.net/manual/en/function.is-numeric.php', 1),
'is_string' => array('is_string', 'LEMis_string', $this->gT('Find whether the type of a variable is string'), 'bool is_string(var)', 'http://www.php.net/manual/en/function.is-string.php', 1),
'join' => array('exprmgr_join', 'LEMjoin', $this->gT('Join strings, return joined string.This function is an alias of implode("",argN)'), 'string join(arg1,arg2,...,argN)', '', -1),
'list' => array('exprmgr_list', 'LEMlist', $this->gT('Return comma-separated list of values'), 'string list(arg1, arg2, ... argN)', '', -2),
'log' => array('log', 'Math.log', $this->gT('Natural logarithm'), 'number log(number)', 'http://www.php.net/manual/en/function.log.php', 1),
'ltrim' => array('ltrim', 'ltrim', $this->gT('Strip whitespace (or other characters) from the beginning of a string'), 'string ltrim(string [, charlist])', 'http://www.php.net/manual/en/function.ltrim.php', 1,2),
'max' => array('max', 'Math.max', $this->gT('Find highest value'), 'number max(arg1, arg2, ... argN)', 'http://www.php.net/manual/en/function.max.php', -2),
'min' => array('min', 'Math.min', $this->gT('Find lowest value'), 'number min(arg1, arg2, ... argN)', 'http://www.php.net/manual/en/function.min.php', -2),
'mktime' => array('mktime', 'mktime', $this->gT('Get UNIX timestamp for a date (each of the 6 arguments are optional)'), 'number mktime([hour [, minute [, second [, month [, day [, year ]]]]]])', 'http://www.php.net/manual/en/function.mktime.php', 0,1,2,3,4,5,6),
'nl2br' => array('nl2br', 'nl2br', $this->gT('Inserts HTML line breaks before all newlines in a string'), 'string nl2br(string)', 'http://www.php.net/manual/en/function.nl2br.php', 1,1),
'number_format' => array('number_format', 'number_format', $this->gT('Format a number with grouped thousands'), 'string number_format(number)', 'http://www.php.net/manual/en/function.number-format.php', 1),
'pi' => array('pi', 'LEMpi', $this->gT('Get value of pi'), 'number pi()', '', 0),
'pow' => array('pow', 'Math.pow', $this->gT('Exponential expression'), 'number pow(base, exp)', 'http://www.php.net/manual/en/function.pow.php', 2),
'quoted_printable_decode' => array('quoted_printable_decode', 'quoted_printable_decode', $this->gT('Convert a quoted-printable string to an 8 bit string'), 'string quoted_printable_decode(string)', 'http://www.php.net/manual/en/function.quoted-printable-decode.php', 1),
'quoted_printable_encode' => array('quoted_printable_encode', 'quoted_printable_encode', $this->gT('Convert a 8 bit string to a quoted-printable string'), 'string quoted_printable_encode(string)', 'http://www.php.net/manual/en/function.quoted-printable-encode.php', 1),
'quotemeta' => array('quotemeta', 'quotemeta', $this->gT('Quote meta characters'), 'string quotemeta(string)', 'http://www.php.net/manual/en/function.quotemeta.php', 1),
'rand' => array('rand', 'rand', $this->gT('Generate a random integer'), 'int rand() OR int rand(min, max)', 'http://www.php.net/manual/en/function.rand.php', 0,2),
'regexMatch' => array('exprmgr_regexMatch', 'LEMregexMatch', $this->gT('Compare a string to a regular expression pattern'), 'bool regexMatch(pattern,input)', '', 2),
'round' => array('round', 'round', $this->gT('Rounds a number to an optional precision'), 'number round(val [, precision])', 'http://www.php.net/manual/en/function.round.php', 1,2),
'rtrim' => array('rtrim', 'rtrim', $this->gT('Strip whitespace (or other characters) from the end of a string'), 'string rtrim(string [, charlist])', 'http://www.php.net/manual/en/function.rtrim.php', 1,2),
'sin' => array('sin', 'Math.sin', $this->gT('Sine'), 'number sin(arg)', 'http://www.php.net/manual/en/function.sin.php', 1),
'sprintf' => array('sprintf', 'sprintf', $this->gT('Return a formatted string'), 'string sprintf(format, arg1, arg2, ... argN)', 'http://www.php.net/manual/en/function.sprintf.php', -2),
'sqrt' => array('sqrt', 'Math.sqrt', $this->gT('Square root'), 'number sqrt(arg)', 'http://www.php.net/manual/en/function.sqrt.php', 1),
'stddev' => array('exprmgr_stddev', 'LEMstddev', $this->gT('Calculate the Sample Standard Deviation for the list of numbers'), 'number stddev(arg1, arg2, ... argN)', '', -2),
'str_pad' => array('str_pad', 'str_pad', $this->gT('Pad a string to a certain length with another string'), 'string str_pad(input, pad_length [, pad_string])', 'http://www.php.net/manual/en/function.str-pad.php', 2,3),
'str_repeat' => array('str_repeat', 'str_repeat', $this->gT('Repeat a string'), 'string str_repeat(input, multiplier)', 'http://www.php.net/manual/en/function.str-repeat.php', 2),
'str_replace' => array('str_replace', 'LEMstr_replace', $this->gT('Replace all occurrences of the search string with the replacement string'), 'string str_replace(search,  replace, subject)', 'http://www.php.net/manual/en/function.str-replace.php', 3),
'strcasecmp' => array('strcasecmp', 'strcasecmp', $this->gT('Binary safe case-insensitive string comparison'), 'int strcasecmp(str1, str2)', 'http://www.php.net/manual/en/function.strcasecmp.php', 2),
'strcmp' => array('strcmp', 'strcmp', $this->gT('Binary safe string comparison'), 'int strcmp(str1, str2)', 'http://www.php.net/manual/en/function.strcmp.php', 2),
'strip_tags' => array('strip_tags', 'strip_tags', $this->gT('Strip HTML and PHP tags from a string'), 'string strip_tags(str, allowable_tags)', 'http://www.php.net/manual/en/function.strip-tags.php', 1,2),
'stripos' => array('stripos', 'stripos', $this->gT('Find position of first occurrence of a case-insensitive string'), 'int stripos(haystack, needle [, offset=0])', 'http://www.php.net/manual/en/function.stripos.php', 2,3),
'stripslashes' => array('stripslashes', 'stripslashes', $this->gT('Un-quotes a quoted string'), 'string stripslashes(string)', 'http://www.php.net/manual/en/function.stripslashes.php', 1),
'stristr' => array('stristr', 'stristr', $this->gT('Case-insensitive strstr'), 'string stristr(haystack, needle [, before_needle=false])', 'http://www.php.net/manual/en/function.stristr.php', 2,3),
'strlen' => array('strlen', 'LEMstrlen', $this->gT('Get string length'), 'int strlen(string)', 'http://www.php.net/manual/en/function.strlen.php', 1),
'strpos' => array('strpos', 'LEMstrpos', $this->gT('Find position of first occurrence of a string'), 'int strpos(haystack, needle [ offset=0])', 'http://www.php.net/manual/en/function.strpos.php', 2,3),
'strrev' => array('strrev', 'strrev', $this->gT('Reverse a string'), 'string strrev(string)', 'http://www.php.net/manual/en/function.strrev.php', 1),
'strstr' => array('strstr', 'strstr', $this->gT('Find first occurrence of a string'), 'string strstr(haystack, needle)', 'http://www.php.net/manual/en/function.strstr.php', 2),
'strtolower' => array('strtolower', 'LEMstrtolower', $this->gT('Make a string lowercase'), 'string strtolower(string)', 'http://www.php.net/manual/en/function.strtolower.php', 1),
'strtoupper' => array('strtoupper', 'LEMstrtoupper', $this->gT('Make a string uppercase'), 'string strtoupper(string)', 'http://www.php.net/manual/en/function.strtoupper.php', 1),
'substr' => array('substr', 'substr', $this->gT('Return part of a string'), 'string substr(string, start [, length])', 'http://www.php.net/manual/en/function.substr.php', 2,3),
'sum' => array('array_sum', 'LEMsum', $this->gT('Calculate the sum of values in an array'), 'number sum(arg1, arg2, ... argN)', '', -2),
'sumifop' => array('exprmgr_sumifop', 'LEMsumifop', $this->gT('Sum the values of answered questions in the list which pass the critiera (arg op value)'), 'number sumifop(op, value, arg1, arg2, ... argN)', '', -3),
'tan' => array('tan', 'Math.tan', $this->gT('Tangent'), 'number tan(arg)', 'http://www.php.net/manual/en/function.tan.php', 1),
'time' => array('time', 'time', $this->gT('Return current UNIX timestamp'), 'number time()', 'http://www.php.net/manual/en/function.time.php', 0),
'trim' => array('trim', 'trim', $this->gT('Strip whitespace (or other characters) from the beginning and end of a string'), 'string trim(string [, charlist])', 'http://www.php.net/manual/en/function.trim.php', 1,2),
'ucwords' => array('ucwords', 'ucwords', $this->gT('Uppercase the first character of each word in a string'), 'string ucwords(string)', 'http://www.php.net/manual/en/function.ucwords.php', 1),
'unique' => array('exprmgr_unique', 'LEMunique', $this->gT('Returns true if all non-empty responses are unique'), 'boolean unique(arg1, ..., argN)', '', -1),
        );

    }

    /**
     * Add an error to the error log
     *
     * @param <type> $errMsg
     * @param <type> $token
     */
    private function RDP_AddError($errMsg, $token)
    {
        $this->RDP_errs[] = array($errMsg, $token);
    }

    /**
     * RDP_EvaluateBinary() computes binary expressions, such as (a or b), (c * d), popping  the top two entries off the
     * stack and pushing the result back onto the stack.
     *
     * @param array $token
     * @return boolean - false if there is any error, else true
     */

       private function RDP_EvaluateBinary(array $token)
    {
        if (count($this->RDP_stack) < 2)
        {
            $this->RDP_AddError($this->gT("Unable to evaluate binary operator - fewer than 2 entries on stack"), $token);
            return false;
        }
        $arg2 = $this->RDP_StackPop();
        $arg1 = $this->RDP_StackPop();
        if (is_null($arg1) or is_null($arg2))
        {
            $this->RDP_AddError($this->gT("Invalid value(s) on the stack"), $token);
            return false;
        }
        // TODO:  try to determine datatype?
        $bNumericArg1 = is_numeric($arg1[0]) || $arg1[0] == '';
        $bNumericArg2 = is_numeric($arg2[0]) || $arg2[0] == '';
        $bStringArg1 = !$bNumericArg1 || $arg1[0] == '';
        $bStringArg2 = !$bNumericArg2 || $arg2[0] == '';
        $bBothNumeric = ($bNumericArg1 && $bNumericArg2);
        $bBothString = ($bStringArg1 && $bStringArg2);
        $bMismatchType = (!$bBothNumeric && !$bBothString);
        switch(strtolower($token[0]))
        {
            case 'or':
            case '||':
                $result = array(($arg1[0] or $arg2[0]),$token[1],'NUMBER');
                break;
            case 'and':
            case '&&':
                $result = array(($arg1[0] and $arg2[0]),$token[1],'NUMBER');
                break;
            case '==':
            case 'eq':
                $result = array(($arg1[0] == $arg2[0]),$token[1],'NUMBER');
                break;
            case '!=':
            case 'ne':
                $result = array(($arg1[0] != $arg2[0]),$token[1],'NUMBER');
                break;
            case '<':
            case 'lt':
                if ($bMismatchType) {
                    $result = array(false,$token[1],'NUMBER');
                }
                else {
                    $result = array(($arg1[0] < $arg2[0]),$token[1],'NUMBER');
                }
                break;
            case '<=';
            case 'le':
                if ($bMismatchType) {
                    $result = array(false,$token[1],'NUMBER');
                }
                else {
                    // Need this explicit comparison in order to be in agreement with JavaScript
                    if (($arg1[0] == '0' && $arg2[0] == '') || ($arg1[0] == '' && $arg2[0] == '0')) {
                        $result = array(true,$token[1],'NUMBER');
                    }
                    else {
                        $result = array(($arg1[0] <= $arg2[0]),$token[1],'NUMBER');
                    }
                }
                break;
            case '>':
            case 'gt':
                if ($bMismatchType) {
                    $result = array(false,$token[1],'NUMBER');
                }
                else {
                    // Need this explicit comparison in order to be in agreement with JavaScript
                    if (($arg1[0] == '0' && $arg2[0] == '') || ($arg1[0] == '' && $arg2[0] == '0')) {
                        $result = array(false,$token[1],'NUMBER');
                    }
                    else {
                        $result = array(($arg1[0] > $arg2[0]),$token[1],'NUMBER');
                    }
                }
                break;
            case '>=';
            case 'ge':
                if ($bMismatchType) {
                    $result = array(false,$token[1],'NUMBER');
                }
                else {
                    $result = array(($arg1[0] >= $arg2[0]),$token[1],'NUMBER');

                }
                break;
            case '+':
                if ($bBothNumeric) {
                    $result = array(($arg1[0] + $arg2[0]),$token[1],'NUMBER');
                }
                else {
                    $result = array($arg1[0] . $arg2[0],$token[1],'STRING');
                }
                break;
            case '-':
                if ($bBothNumeric) {
                    $result = array(($arg1[0] - $arg2[0]),$token[1],'NUMBER');
                }
                else {
                    $result = array(NAN,$token[1],'NUMBER');
                }
                break;
            case '*':
                if ($bBothNumeric) {
                    $result = array(($arg1[0] * $arg2[0]),$token[1],'NUMBER');
                }
                else {
                    $result = array(NAN,$token[1],'NUMBER');
                }
                break;
            case '/';
                if ($bBothNumeric) {
                    if ($arg2[0] == 0) {
                        $result = array(NAN,$token[1],'NUMBER');
                    }
                    else {
                        $result = array(($arg1[0] / $arg2[0]),$token[1],'NUMBER');
                    }
                }
                else {
                    $result = array(NAN,$token[1],'NUMBER');
                }
                break;
        }
        $this->RDP_StackPush($result);
        return true;
    }

    /**
     * Processes operations like +a, -b, !c
     * @param array $token
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateUnary(array $token)
    {
        if (count($this->RDP_stack) < 1)
        {
            $this->RDP_AddError($this->gT("Unable to evaluate unary operator - no entries on stack"), $token);
            return false;
        }
        $arg1 = $this->RDP_StackPop();
        if (is_null($arg1))
        {
            $this->RDP_AddError($this->gT("Invalid value(s) on the stack"), $token);
            return false;
        }
        // TODO:  try to determine datatype?
        switch($token[0])
        {
            case '+':
                $result = array((+$arg1[0]),$token[1],'NUMBER');
                break;
            case '-':
                $result = array((-$arg1[0]),$token[1],'NUMBER');
                break;
            case '!';
                $result = array((!$arg1[0]),$token[1],'NUMBER');
                break;
        }
        $this->RDP_StackPush($result);
        return true;
    }


    /**
     * Main entry function
     * @param <type> $expr
     * @param <type> $onlyparse - if true, then validate the syntax without computing an answer
     * @return boolean - true if success, false if any error occurred
     */

    public function RDP_Evaluate($expr, $onlyparse=false)
    {
        $this->RDP_expr = $expr;
        $this->RDP_tokens = $this->RDP_Tokenize($expr);
        $this->RDP_count = count($this->RDP_tokens);
        $this->RDP_pos = -1; // starting position within array (first act will be to increment it)
        $this->RDP_errs = array();
        $this->RDP_onlyparse = $onlyparse;
        $this->RDP_stack = array();
        $this->RDP_evalStatus = false;
        $this->RDP_result = NULL;
        $this->varsUsed = array();
        $this->jsExpression = NULL;

        if ($this->HasSyntaxErrors()) {
            return false;
        }
        elseif ($this->RDP_EvaluateExpressions())
        {
            if ($this->RDP_pos < $this->RDP_count)
            {
                $this->RDP_AddError($this->gT("Extra tokens found"), $this->RDP_tokens[$this->RDP_pos]);
                return false;
            }
            $this->RDP_result = $this->RDP_StackPop();
            if (is_null($this->RDP_result))
            {
                return false;
            }
            if (count($this->RDP_stack) == 0)
            {
                $this->RDP_evalStatus = true;
                return true;
            }
            else
            {
                $this-RDP_AddError($this->gT("Unbalanced equation - values left on stack"),NULL);
                return false;
            }
        }
        else
        {
            $this->RDP_AddError($this->gT("Not a valid expression"),NULL);
            return false;
        }
    }


    /**
     * Process "a op b" where op in (+,-,concatenate)
     * @return boolean - true if success, false if any error occurred
     */
    private function RDP_EvaluateAdditiveExpression()
    {
        if (!$this->RDP_EvaluateMultiplicativeExpression())
        {
            return false;
        }
        while (($this->RDP_pos + 1) < $this->RDP_count)
        {
            $token = $this->RDP_tokens[++$this->RDP_pos];
            if ($token[2] == 'BINARYOP')
            {
                switch ($token[0])
                {
                    case '+':
                    case '-';
                        if ($this->RDP_EvaluateMultiplicativeExpression())
                        {
                            if (!$this->RDP_EvaluateBinary($token))
                            {
                                return false;
                            }
                            // else continue;
                        }
                        else
                        {
                            return false;
                        }
                        break;
                    default:
                        --$this->RDP_pos;
                        return true;
                }
            }
            else
            {
                --$this->RDP_pos;
                return true;
            }
        }
        return true;
    }

    /**
     * Process a Constant (number of string), retrieve the value of a known variable, or process a function, returning result on the stack.
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateConstantVarOrFunction()
    {
        if ($this->RDP_pos + 1 >= $this->RDP_count)
        {
             $this->RDP_AddError($this->gT("Poorly terminated expression - expected a constant or variable"), NULL);
             return false;
        }
        $token = $this->RDP_tokens[++$this->RDP_pos];
        switch ($token[2])
        {
            case 'NUMBER':
            case 'DQ_STRING':
            case 'SQ_STRING':
                $this->RDP_StackPush($token);
                return true;
                break;
            case 'WORD':
            case 'SGQA':
                if (($this->RDP_pos + 1) < $this->RDP_count and $this->RDP_tokens[($this->RDP_pos + 1)][2] == 'LP')
                {
                    return $this->RDP_EvaluateFunction();
                }
                else
                {
                    if ($this->RDP_isValidVariable($token[0]))
                    {
                        $this->varsUsed[] = $token[0];  // add this variable to list of those used in this equation
                        if (preg_match("/\.(gid|grelevance|gseq|jsName|mandatory|qid|qseq|question|readWrite|relevance|rowdivid|sgqa|type)$/",$token[0]))
                        {
                            $relStatus=1;   // static, so always relevant
                        }
                        else
                        {
                            $relStatus = $this->GetVarAttribute($token[0],'relevanceStatus',1);
                        }
                        if ($relStatus==1)
                        {
                            $result = array($this->GetVarAttribute($token[0],NULL,''),$token[1],'NUMBER');
                        }
                        else
                        {
                            $result = array(NULL,$token[1],'NUMBER');   // was 0 instead of NULL
                        }
                        $this->RDP_StackPush($result);

                        // TODO - currently, will try to process value anyway, but want to show a potential error.  Should it be a definitive error (e.g. prevent this behavior)?
                        $groupSeq = $this->GetVarAttribute($token[0],'gseq',-1);
                        if (($groupSeq != -1 && $this->groupSeq != -1) && ($groupSeq > $this->groupSeq))
                        {
                            $this->RDP_AddError($this->gT("Variable not declared until a later page"),$token);
                            return false;
                        }
                        return true;
                    }
                    else
                    {
                        $this->RDP_AddError($this->gT("Undefined variable"), $token);
                        return false;
                    }
                }
                break;
            case 'COMMA':
                --$this->RDP_pos;
                $this->RDP_AddError($this->gT("Should never  get to this line?"),$token);
                return false;
            default:
                return false;
                break;
        }
    }

    /**
     * Process "a == b", "a eq b", "a != b", "a ne b"
     * @return boolean - true if success, false if any error occurred
     */
    private function RDP_EvaluateEqualityExpression()
    {
        if (!$this->RDP_EvaluateRelationExpression())
        {
            return false;
        }
        while (($this->RDP_pos + 1) < $this->RDP_count)
        {
            $token = $this->RDP_tokens[++$this->RDP_pos];
            switch (strtolower($token[0]))
            {
                case '==':
                case 'eq':
                case '!=':
                case 'ne':
                    if ($this->RDP_EvaluateRelationExpression())
                    {
                        if (!$this->RDP_EvaluateBinary($token))
                        {
                            return false;
                        }
                        // else continue;
                    }
                    else
                    {
                        return false;
                    }
                    break;
                default:
                    --$this->RDP_pos;
                    return true;
            }
        }
        return true;
    }

    /**
     * Process a single expression (e.g. without commas)
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateExpression()
    {
        if ($this->RDP_pos + 2 < $this->RDP_count)
        {
            $token1 = $this->RDP_tokens[++$this->RDP_pos];
            $token2 = $this->RDP_tokens[++$this->RDP_pos];
            if ($token2[2] == 'ASSIGN')
            {
                if ($this->RDP_isValidVariable($token1[0]))
                {
                    $this->varsUsed[] = $token1[0];  // add this variable to list of those used in this equation
                    if ($this->RDP_isWritableVariable($token1[0]))
                    {
                        $evalStatus = $this->RDP_EvaluateLogicalOrExpression();
                        if ($evalStatus)
                        {
                            $result = $this->RDP_StackPop();
                            if (!is_null($result))
                            {
                                $newResult = $token2;
                                $newResult[2] = 'NUMBER';
                                $newResult[0] = $this->RDP_SetVariableValue($token2[0], $token1[0], $result[0]);
                                $this->RDP_StackPush($newResult);
                            }
                            else
                            {
                                $evalStatus = false;
                            }
                        }
                        return $evalStatus;
                    }
                    else
                    {
                        $this->RDP_AddError($this->gT('The value of this variable can not be changed'), $token1);
                        return false;
                    }
                }
                else
                {
                    $this->RDP_AddError($this->gT('Only variables can be assigned values'), $token1);
                    return false;
                }
            }
            else
            {
                // not an assignment expression, so try something else
                $this->RDP_pos -= 2;
                return $this->RDP_EvaluateLogicalOrExpression();
            }
        }
        else
        {
            return $this->RDP_EvaluateLogicalOrExpression();
        }
    }

    /**
     * Process "expression [, expression]*
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateExpressions()
    {
        $evalStatus = $this->RDP_EvaluateExpression();
        if (!$evalStatus)
        {
            return false;
        }

        while (++$this->RDP_pos < $this->RDP_count) {
            $token = $this->RDP_tokens[$this->RDP_pos];
            if ($token[2] == 'RP')
            {
                return true;    // presumbably the end of an expression
            }
            elseif ($token[2] == 'COMMA')
            {
                if ($this->RDP_EvaluateExpression())
                {
                    $secondResult = $this->RDP_StackPop();
                    $firstResult = $this->RDP_StackPop();
                    if (is_null($firstResult))
                    {
                        return false;
                    }
                    $this->RDP_StackPush($secondResult);
                    $evalStatus = true;
                }
                else
                {
                    return false;   // an error must have occurred
                }
            }
            else
            {
                $this->RDP_AddError($this->gT("Expected expressions separated by commas"),$token);
                $evalStatus = false;
                break;
            }
        }
        while (++$this->RDP_pos < $this->RDP_count)
        {
            $token = $this->RDP_tokens[$this->RDP_pos];
            $this->RDP_AddError($this->gT("Extra token found after expressions"),$token);
            $evalStatus = false;
        }
        return $evalStatus;
    }

    /**
     * Process a function call
     * @return boolean - true if success, false if any error occurred
     */
    private function RDP_EvaluateFunction()
    {
        $funcNameToken = $this->RDP_tokens[$this->RDP_pos]; // note that don't need to increment position for functions
        $funcName = $funcNameToken[0];
        if (!$this->RDP_isValidFunction($funcName))
        {
            $this->RDP_AddError($this->gT("Undefined function"), $funcNameToken);
            return false;
        }
        $token2 = $this->RDP_tokens[++$this->RDP_pos];
        if ($token2[2] != 'LP')
        {
            $this->RDP_AddError($this->gT("Expected left parentheses after function name"), $funcNameToken);
        }
        $params = array();  // will just store array of values, not tokens
        while ($this->RDP_pos + 1 < $this->RDP_count)
        {
            $token3 = $this->RDP_tokens[$this->RDP_pos + 1];
            if (count($params) > 0)
            {
                // should have COMMA or RP
                if ($token3[2] == 'COMMA')
                {
                    ++$this->RDP_pos;   // consume the token so can process next clause
                    if ($this->RDP_EvaluateExpression())
                    {
                        $value = $this->RDP_StackPop();
                        if (is_null($value))
                        {
                            return false;
                        }
                        $params[] = $value[0];
                        continue;
                    }
                    else
                    {
                        $this->RDP_AddError($this->gT("Extra comma found in function"), $token3);
                        return false;
                    }
                }
            }
            if ($token3[2] == 'RP')
            {
                ++$this->RDP_pos;   // consume the token so can process next clause
                return $this->RDP_RunFunction($funcNameToken,$params);
            }
            else
            {
                if ($this->RDP_EvaluateExpression())
                {
                    $value = $this->RDP_StackPop();
                    if (is_null($value))
                    {
                        return false;
                    }
                    $params[] = $value[0];
                    continue;
                }
                else
                {
                    return false;
                }
            }
        }
    }

    /**
     * Process "a && b" or "a and b"
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateLogicalAndExpression()
    {
        if (!$this->RDP_EvaluateEqualityExpression())
        {
            return false;
        }
        while (($this->RDP_pos + 1) < $this->RDP_count)
        {
            $token = $this->RDP_tokens[++$this->RDP_pos];
            switch (strtolower($token[0]))
            {
                case '&&':
                case 'and':
                    if ($this->RDP_EvaluateEqualityExpression())
                    {
                        if (!$this->RDP_EvaluateBinary($token))
                        {
                            return false;
                        }
                        // else continue
                    }
                    else
                    {
                        return false;   // an error must have occurred
                    }
                    break;
                default:
                    --$this->RDP_pos;
                    return true;
            }
        }
        return true;
    }

    /**
     * Process "a || b" or "a or b"
     * @return boolean - true if success, false if any error occurred
     */
    private function RDP_EvaluateLogicalOrExpression()
    {
        if (!$this->RDP_EvaluateLogicalAndExpression())
        {
            return false;
        }
        while (($this->RDP_pos + 1) < $this->RDP_count)
        {
            $token = $this->RDP_tokens[++$this->RDP_pos];
            switch (strtolower($token[0]))
            {
                case '||':
                case 'or':
                    if ($this->RDP_EvaluateLogicalAndExpression())
                    {
                        if (!$this->RDP_EvaluateBinary($token))
                        {
                            return false;
                        }
                        // else  continue
                    }
                    else
                    {
                        // an error must have occurred
                        return false;
                    }
                    break;
                default:
                    // no more expressions being  ORed together, so continue parsing
                    --$this->RDP_pos;
                    return true;
            }
        }
        // no more tokens to parse
        return true;
    }

    /**
     * Process "a op b" where op in (*,/)
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateMultiplicativeExpression()
    {
        if (!$this->RDP_EvaluateUnaryExpression())
        {
            return  false;
        }
        while (($this->RDP_pos + 1) < $this->RDP_count)
        {
            $token = $this->RDP_tokens[++$this->RDP_pos];
            if ($token[2] == 'BINARYOP')
            {
                switch ($token[0])
                {
                    case '*':
                    case '/';
                        if ($this->RDP_EvaluateUnaryExpression())
                        {
                            if (!$this->RDP_EvaluateBinary($token))
                            {
                                return false;
                            }
                            // else  continue
                        }
                        else
                        {
                            // an error must have occurred
                            return false;
                        }
                        break;
                        break;
                    default:
                        --$this->RDP_pos;
                        return true;
                }
            }
            else
            {
                --$this->RDP_pos;
                return true;
            }
        }
        return true;
    }

    /**
     * Process expressions including functions and parenthesized blocks
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluatePrimaryExpression()
    {
        if (($this->RDP_pos + 1) >= $this->RDP_count) {
            $this->RDP_AddError($this->gT("Poorly terminated expression - expected a constant or variable"), NULL);
            return false;
        }
        $token = $this->RDP_tokens[++$this->RDP_pos];
        if ($token[2] == 'LP')
        {
            if (!$this->RDP_EvaluateExpressions())
            {
                return false;
            }
            $token = $this->RDP_tokens[$this->RDP_pos];
            if ($token[2] == 'RP')
            {
                return true;
            }
            else
            {
                $this->RDP_AddError($this->gT("Expected right parentheses"), $token);
                return false;
            }
        }
        else
        {
            --$this->RDP_pos;
            return $this->RDP_EvaluateConstantVarOrFunction();
        }
    }

    /**
     * Process "a op b" where op in (lt, gt, le, ge, <, >, <=, >=)
     * @return boolean - true if success, false if any error occurred
     */
    private function RDP_EvaluateRelationExpression()
    {
        if (!$this->RDP_EvaluateAdditiveExpression())
        {
            return false;
        }
        while (($this->RDP_pos + 1) < $this->RDP_count)
        {
            $token = $this->RDP_tokens[++$this->RDP_pos];
            switch (strtolower($token[0]))
            {
                case '<':
                case 'lt':
                case '<=';
                case 'le':
                case '>':
                case 'gt':
                case '>=';
                case 'ge':
                    if ($this->RDP_EvaluateAdditiveExpression())
                    {
                        if (!$this->RDP_EvaluateBinary($token))
                        {
                            return false;
                        }
                        // else  continue
                    }
                    else
                    {
                        // an error must have occurred
                        return false;
                    }
                    break;
                default:
                    --$this->RDP_pos;
                    return true;
            }
        }
        return true;
    }

    /**
     * Process "op a" where op in (+,-,!)
     * @return boolean - true if success, false if any error occurred
     */

    private function RDP_EvaluateUnaryExpression()
    {
        if (($this->RDP_pos + 1) >= $this->RDP_count) {
            $this->RDP_AddError($this->gT("Poorly terminated expression - expected a constant or variable"), NULL);
            return false;
        }
        $token = $this->RDP_tokens[++$this->RDP_pos];
        if ($token[2] == 'NOT' || $token[2] == 'BINARYOP')
        {
            switch ($token[0])
            {
                case '+':
                case '-':
                case '!':
                    if (!$this->RDP_EvaluatePrimaryExpression())
                    {
                        return false;
                    }
                    return $this->RDP_EvaluateUnary($token);
                    break;
                default:
                    --$this->RDP_pos;
                    return $this->RDP_EvaluatePrimaryExpression();
            }
        }
        else
        {
            --$this->RDP_pos;
            return $this->RDP_EvaluatePrimaryExpression();
        }
    }

    /**
     * Returns array of al…

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