math-expr.inc

<?php


/**
 * @file
 * =============================================================================.
 *
 * ctools_math_expr - PHP Class to safely evaluate math expressions
 * Copyright (C) 2005 Miles Kaufmann <http://www.twmagic.com/>
 *
 * =============================================================================
 *
 * NAME
 *     ctools_math_expr - safely evaluate math expressions
 *
 * SYNOPSIS
 *     $m = new ctools_math_expr();
 *     // basic evaluation:
 *     $result = $m->evaluate('2+2');
 *     // supports: order of operation; parentheses; negation; built-in
 *     // functions.
 *     $result = $m->evaluate('-8(5/2)^2*(1-sqrt(4))-8');
 *     // create your own variables
 *     $m->evaluate('a = e^(ln(pi))');
 *     // or functions
 *     $m->evaluate('f(x,y) = x^2 + y^2 - 2x*y + 1');
 *     // and then use them
 *     $result = $m->evaluate('3*f(42,a)');
 *
 * DESCRIPTION
 *     Use the ctools_math_expr class when you want to evaluate mathematical
 *     expressions from untrusted sources.  You can define your own variables
 *     and functions, which are stored in the object.  Try it, it's fun!
 *
 * AUTHOR INFORMATION
 *     Copyright 2005, Miles Kaufmann.
 *     Enhancements, 2005 onwards, Drupal Community.
 *
 * LICENSE
 *     Redistribution and use in source and binary forms, with or without
 *     modification, are permitted provided that the following conditions are
 *     met:
 *
 *     1   Redistributions of source code must retain the above copyright
 *         notice, this list of conditions and the following disclaimer.
 *     2.  Redistributions in binary form must reproduce the above copyright
 *         notice, this list of conditions and the following disclaimer in the
 *         documentation and/or other materials provided with the distribution.
 *     3.  The name of the author may not be used to endorse or promote
 *         products derived from this software without specific prior written
 *         permission.
 *
 *     THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *     IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 *     WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *     DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 *     INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 *     (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 *     SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 *     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 *     STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 *     ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *     POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * ctools_math_expr Class.
 */
class ctools_math_expr {
    
    /**
     * If TRUE do not call trigger_error on error other wise do.
     *
     * @var bool
     */
    public $suppress_errors = FALSE;
    
    /**
     * The last error message reported.
     *
     * @var string
     */
    public $last_error = NULL;
    
    /**
     * List of all errors reported.
     *
     * @var array
     */
    public $errors = array();
    
    /**
     * Variable and constant values.
     *
     * @var array
     */
    protected $vars;
    
    /**
     * User defined functions.
     *
     * @var array
     */
    protected $userfuncs;
    
    /**
     * The names of constants, used to make constants read-only.
     *
     * @var array
     */
    protected $constvars;
    
    /**
     * Built in simple (one arg) functions.
     * Merged into $this->funcs in constructor.
     *
     * @var array
     */
    protected $simplefuncs;
    
    /**
     * Definitions of all built-in functions.
     *
     * @var array
     */
    protected $funcs;
    
    /**
     * Operators and their precedence.
     *
     * @var array
     */
    protected $ops;
    
    /**
     * The set of operators using two arguments.
     *
     * @var array
     */
    protected $binaryops;
    
    /**
     * Public constructor.
     */
    public function __construct() {
        $this->userfuncs = array();
        $this->simplefuncs = array(
            'sin',
            'sinh',
            'asin',
            'asinh',
            'cos',
            'cosh',
            'acos',
            'acosh',
            'tan',
            'tanh',
            'atan',
            'atanh',
            'exp',
            'sqrt',
            'abs',
            'log',
            'ceil',
            'floor',
            'round',
        );
        $this->ops = array(
            '+' => array(
                'precedence' => 0,
            ),
            '-' => array(
                'precedence' => 0,
            ),
            '*' => array(
                'precedence' => 1,
            ),
            '/' => array(
                'precedence' => 1,
            ),
            '^' => array(
                'precedence' => 2,
                'right' => TRUE,
            ),
            '_' => array(
                'precedence' => 1,
            ),
            '==' => array(
                'precedence' => -1,
            ),
            '!=' => array(
                'precedence' => -1,
            ),
            '>=' => array(
                'precedence' => -1,
            ),
            '<=' => array(
                'precedence' => -1,
            ),
            '>' => array(
                'precedence' => -1,
            ),
            '<' => array(
                'precedence' => -1,
            ),
        );
        $this->binaryops = array(
            '+',
            '-',
            '*',
            '/',
            '^',
            '==',
            '!=',
            '<',
            '<=',
            '>=',
            '>',
        );
        $this->funcs = array(
            'ln' => array(
                'function' => 'log',
                'arguments' => 1,
            ),
            'arcsin' => array(
                'function' => 'asin',
                'arguments' => 1,
            ),
            'arcsinh' => array(
                'function' => 'asinh',
                'arguments' => 1,
            ),
            'arccos' => array(
                'function' => 'acos',
                'arguments' => 1,
            ),
            'arccosh' => array(
                'function' => 'acosh',
                'arguments' => 1,
            ),
            'arctan' => array(
                'function' => 'atan',
                'arguments' => 1,
            ),
            'arctanh' => array(
                'function' => 'atanh',
                'arguments' => 1,
            ),
            'min' => array(
                'function' => 'min',
                'arguments' => 2,
                'max arguments' => 99,
            ),
            'max' => array(
                'function' => 'max',
                'arguments' => 2,
                'max arguments' => 99,
            ),
            'pow' => array(
                'function' => 'pow',
                'arguments' => 2,
            ),
            'if' => array(
                'function' => 'ctools_math_expr_if',
                'arguments' => 2,
                'max arguments' => 3,
            ),
            'number' => array(
                'function' => 'ctools_math_expr_number',
                'arguments' => 1,
            ),
            'time' => array(
                'function' => 'time',
                'arguments' => 0,
            ),
        );
        // Allow modules to add custom functions.
        $context = array(
            'final' => &$this->funcs,
        );
        drupal_alter('ctools_math_expression_functions', $this->simplefuncs, $context);
        // Set up the initial constants and mark them read-only.
        $this->vars = array(
            'e' => exp(1),
            'pi' => pi(),
        );
        drupal_alter('ctools_math_expression_constants', $this->vars);
        $this->constvars = array_keys($this->vars);
        // Translate the older, simpler style into the newer, richer style.
        foreach ($this->simplefuncs as $function) {
            $this->funcs[$function] = array(
                'function' => $function,
                'arguments' => 1,
            );
        }
    }
    
    /**
     * Change the suppress errors flag.
     *
     * When errors are not suppressed, trigger_error is used to cause a PHP error
     * when an evaluation error occurs, as a result of calling trigger(). With
     * errors suppressed this doesn't happen.
     *
     * @param bool $enable
     *   If FALSE, enable triggering of php errors when expression errors occurs.
     *   otherwise, suppress triggering the errors.
     *
     * @return bool
     *   The new (current) state of the flag.
     *
     * @see ctools_math_expr::trigger()
     */
    public function set_suppress_errors($enable) {
        return $this->suppress_errors = (bool) $enable;
    }
    
    /**
     * Backwards compatible wrapper for evaluate().
     *
     * @see ctools_math_expr::evaluate()
     */
    public function e($expr) {
        return $this->evaluate($expr);
    }
    
    /**
     * Evaluate the expression.
     *
     * @param string $expr
     *   The expression to evaluate.
     *
     * @return string|bool
     *   The result of the expression, or FALSE if an error occurred, or TRUE if
     *   an user-defined function was created.
     */
    public function evaluate($expr) {
        $this->last_error = NULL;
        $expr = trim($expr);
        // Strip possible semicolons at the end.
        if (substr($expr, -1, 1) == ';') {
            $expr = (string) substr($expr, 0, -1);
        }
        // Is it a variable assignment?
        if (preg_match('/^\\s*([a-z]\\w*)\\s*=\\s*(.+)$/', $expr, $matches)) {
            // Make sure we're not assigning to a constant.
            if (in_array($matches[1], $this->constvars)) {
                return $this->trigger("cannot assign to constant '{$matches[1]}'");
            }
            // Get the result and make sure it's good:
            if (($tmp = $this->pfx($this->nfx($matches[2]))) === FALSE) {
                return FALSE;
            }
            // If so, stick it in the variable array...
            $this->vars[$matches[1]] = $tmp;
            // ...and return the resulting value:
            return $this->vars[$matches[1]];
        }
        elseif (preg_match('/^\\s*([a-z]\\w*)\\s*\\(\\s*([a-z]\\w*(?:\\s*,\\s*[a-z]\\w*)*)\\s*\\)\\s*=\\s*(.+)$/', $expr, $matches)) {
            // Get the function name.
            $fnn = $matches[1];
            // Make sure it isn't built in:
            if (isset($this->funcs[$matches[1]])) {
                return $this->trigger("cannot redefine built-in function '{$matches[1]}()'");
            }
            // Get the arguments.
            $args = explode(",", preg_replace("/\\s+/", "", $matches[2]));
            // See if it can be converted to postfix.
            $stack = $this->nfx($matches[3]);
            if ($stack === FALSE) {
                return FALSE;
            }
            // Freeze the state of the non-argument variables.
            for ($i = 0; $i < count($stack); $i++) {
                $token = (string) $stack[$i];
                if (preg_match('/^[a-z]\\w*$/', $token) and !in_array($token, $args)) {
                    if (array_key_exists($token, $this->vars)) {
                        $stack[$i] = $this->vars[$token];
                    }
                    else {
                        return $this->trigger("undefined variable '{$token}' in function definition");
                    }
                }
            }
            $this->userfuncs[$fnn] = array(
                'args' => $args,
                'func' => $stack,
            );
            return TRUE;
        }
        else {
            // Straight up evaluation.
            return trim($this->pfx($this->nfx($expr)), '"');
        }
    }
    
    /**
     * Fetch an array of variables used in the expression.
     *
     * @return array
     *   Array of name : value pairs, one for each variable defined.
     */
    public function vars() {
        $output = $this->vars;
        // @todo: Is this supposed to remove all constants? we should remove all
        // those in $this->constvars!
        unset($output['pi']);
        unset($output['e']);
        return $output;
    }
    
    /**
     * Fetch all user defined functions in the expression.
     *
     * @return array
     *   Array of name : string pairs, one for each function defined. The string
     *   will be of the form fname(arg1,arg2). The function body is not returned.
     */
    public function funcs() {
        $output = array();
        foreach ($this->userfuncs as $fnn => $dat) {
            $output[] = $fnn . '(' . implode(',', $dat['args']) . ')';
        }
        return $output;
    }
    
    /**
     * Convert infix to postfix notation.
     *
     * @param string $expr
     *   The expression to convert.
     *
     * @return array|bool
     *   The expression as an ordered list of postfix action tokens.
     */
    private function nfx($expr) {
        $index = 0;
        $stack = new ctools_math_expr_stack();
        // Postfix form of expression, to be passed to pfx().
        $output = array();
        // @todo: Because the expr can contain string operands, using strtolower here is a bug.
        $expr = trim(strtolower($expr));
        // We use this in syntax-checking the expression and determining when
        // '-' is a negation.
        $expecting_op = FALSE;
        while (TRUE) {
            $op = substr($expr, $index, 1);
            // Get the first character at the current index, and if the second
            // character is an =, add it to our op as well (accounts for <=).
            if (substr($expr, $index + 1, 1) === '=') {
                $op = substr($expr, $index, 2);
                $index++;
            }
            // Find out if we're currently at the beginning of a number/variable/
            // function/parenthesis/operand.
            $ex = preg_match('/^([a-z]\\w*\\(?|\\d+(?:\\.\\d*)?|\\.\\d+|\\()/', (string) substr($expr, $index), $match);
            // Is it a negation instead of a minus?
            if ($op === '-' and !$expecting_op) {
                // Put a negation on the stack.
                $stack->push('_');
                $index++;
            }
            elseif ($op == '_') {
                return $this->trigger("illegal character '_'");
            }
            elseif ((isset($this->ops[$op]) || $ex) && $expecting_op) {
                // Are we expecting an operator but have a num, var, func, or
                // open-paren?
                if ($ex) {
                    $op = '*';
                    // It's an implicit multiplication.
                    $index--;
                }
                // Heart of the algorithm:
                while ($stack->count() > 0 && ($o2 = $stack->last()) && isset($this->ops[$o2]) && (!empty($this->ops[$op]['right']) ? $this->ops[$op]['precedence'] < $this->ops[$o2]['precedence'] : $this->ops[$op]['precedence'] <= $this->ops[$o2]['precedence'])) {
                    // Pop stuff off the stack into the output.
                    $output[] = $stack->pop();
                }
                // Many thanks: http://en.wikipedia.org/wiki/Reverse_Polish_notation#The_algorithm_in_detail
                // finally put OUR operator onto the stack.
                $stack->push($op);
                $index++;
                $expecting_op = FALSE;
            }
            elseif ($op === ')') {
                // Pop off the stack back to the last '('.
                while (($o2 = $stack->pop()) !== '(') {
                    if (is_null($o2)) {
                        return $this->trigger("unexpected ')'");
                    }
                    else {
                        $output[] = $o2;
                    }
                }
                // Did we just close a function?
                if (preg_match("/^([a-z]\\w*)\\(\$/", (string) $stack->last(2), $matches)) {
                    // Get the function name.
                    $fnn = $matches[1];
                    // See how many arguments there were (cleverly stored on the stack,
                    // thank you).
                    $arg_count = $stack->pop();
                    // Pop the function and push onto the output.
                    $output[] = $stack->pop();
                    // Check the argument count:
                    if (isset($this->funcs[$fnn])) {
                        $fdef = $this->funcs[$fnn];
                        $max_arguments = isset($fdef['max arguments']) ? $fdef['max arguments'] : $fdef['arguments'];
                        if ($arg_count > $max_arguments) {
                            return $this->trigger("too many arguments ({$arg_count} given, {$max_arguments} expected)");
                        }
                    }
                    elseif (array_key_exists($fnn, $this->userfuncs)) {
                        $fdef = $this->userfuncs[$fnn];
                        if ($arg_count !== count($fdef['args'])) {
                            return $this->trigger("wrong number of arguments ({$arg_count} given, " . count($fdef['args']) . ' expected)');
                        }
                    }
                    else {
                        // Did we somehow push a non-function on the stack? this should
                        // never happen.
                        return $this->trigger('internal error');
                    }
                }
                $index++;
            }
            elseif ($op === ',' && $expecting_op) {
                $index++;
                $expecting_op = FALSE;
            }
            elseif ($op === '(' && !$expecting_op) {
                $stack->push('(');
                $index++;
            }
            elseif ($ex && !$expecting_op) {
                // Make sure there was a function.
                if (preg_match("/^([a-z]\\w*)\\(\$/", (string) $stack->last(3), $matches)) {
                    // Pop the argument expression stuff and push onto the output:
                    while (($o2 = $stack->pop()) !== '(') {
                        // Oops, never had a '('.
                        if (is_null($o2)) {
                            return $this->trigger("unexpected argument in {$expr} {$o2}");
                        }
                        else {
                            $output[] = $o2;
                        }
                    }
                    // Increment the argument count.
                    $stack->push($stack->pop() + 1);
                    // Put the ( back on, we'll need to pop back to it again.
                    $stack->push('(');
                }
                // Do we now have a function/variable/number?
                $expecting_op = TRUE;
                $val = (string) $match[1];
                if (preg_match("/^([a-z]\\w*)\\(\$/", $val, $matches)) {
                    // May be func, or variable w/ implicit multiplication against
                    // parentheses...
                    if (isset($this->funcs[$matches[1]]) or array_key_exists($matches[1], $this->userfuncs)) {
                        $stack->push($val);
                        $stack->push(0);
                        $stack->push('(');
                        $expecting_op = FALSE;
                    }
                    else {
                        $val = $matches[1];
                        $output[] = $val;
                    }
                }
                else {
                    $output[] = $val;
                }
                $index += strlen($val);
            }
            elseif ($op === ')') {
                // Miscellaneous error checking.
                return $this->trigger("unexpected ')'");
            }
            elseif (isset($this->ops[$op]) and !$expecting_op) {
                return $this->trigger("unexpected operator '{$op}'");
            }
            elseif ($op === '"') {
                // Fetch a quoted string.
                $string = (string) substr($expr, $index);
                if (preg_match('/"[^"\\\\]*(?:\\\\.[^"\\\\]*)*"/s', $string, $matches)) {
                    $string = $matches[0];
                    // Trim the quotes off:
                    $output[] = $string;
                    $index += strlen($string);
                    $expecting_op = TRUE;
                }
                else {
                    return $this->trigger('open quote without close quote.');
                }
            }
            else {
                // I don't even want to know what you did to get here.
                return $this->trigger("an unexpected error occurred at {$op}");
            }
            if ($index === strlen($expr)) {
                if (isset($this->ops[$op])) {
                    // Did we end with an operator? bad.
                    return $this->trigger("operator '{$op}' lacks operand");
                }
                else {
                    break;
                }
            }
            // Step the index past whitespace (pretty much turns whitespace into
            // implicit multiplication if no operator is there).
            while (substr($expr, $index, 1) === ' ') {
                $index++;
            }
        }
        // Pop everything off the stack and push onto output:
        while (!is_null($op = $stack->pop())) {
            // If there are (s on the stack, ()s were unbalanced.
            if ($op === '(') {
                return $this->trigger("expecting ')'");
            }
            $output[] = $op;
        }
        return $output;
    }
    
    /**
     * Evaluate a prefix-operator stack expression.
     *
     * @param array $tokens
     *   The array of token values to evaluate. A token is a string value
     *   representing either an operation to perform, a variable, or a value.
     *   Literal values are checked using is_numeric(), or a value that starts
     *   with a double-quote; functions and variables by existence in the
     *   appropriate tables.
     *   If FALSE is passed in the function terminates immediately, returning
     *   FALSE.
     * @param array $vars
     *   Additional variable values to use when evaluating the expression. These
     *   variables do not override internal variables with the same name.
     *
     * @return bool|mixed
     *   The expression's value, otherwise FALSE is returned if there is an error
     *   detected unless php error handling intervenes: see suppress_error.
     */
    public function pfx(array $tokens, array $vars = array()) {
        if ($tokens == FALSE) {
            return FALSE;
        }
        $stack = new ctools_math_expr_stack();
        foreach ($tokens as $token) {
            // If the token is a binary operator, pop two values off the stack, do
            // the operation, and push the result back on again.
            if (in_array($token, $this->binaryops)) {
                if (is_null($op2 = $stack->pop())) {
                    return $this->trigger('internal error');
                }
                if (is_null($op1 = $stack->pop())) {
                    return $this->trigger('internal error');
                }
                switch ($token) {
                    case '+':
                        $stack->push($op1 + $op2);
                        break;
                    case '-':
                        $stack->push($op1 - $op2);
                        break;
                    case '*':
                        $stack->push($op1 * $op2);
                        break;
                    case '/':
                        if ($op2 == 0) {
                            return $this->trigger('division by zero');
                        }
                        $stack->push($op1 / $op2);
                        break;
                    case '^':
                        $stack->push(pow($op1, $op2));
                        break;
                    case '==':
                        $stack->push((int) ($op1 == $op2));
                        break;
                    case '!=':
                        $stack->push((int) ($op1 != $op2));
                        break;
                    case '<=':
                        $stack->push((int) ($op1 <= $op2));
                        break;
                    case '<':
                        $stack->push((int) ($op1 < $op2));
                        break;
                    case '>=':
                        $stack->push((int) ($op1 >= $op2));
                        break;
                    case '>':
                        $stack->push((int) ($op1 > $op2));
                        break;
                }
            }
            elseif ($token === "_") {
                $stack->push(-1 * $stack->pop());
            }
            elseif (preg_match("/^([a-z]\\w*)\\(\$/", (string) $token, $matches)) {
                $fnn = $matches[1];
                // Check for a built-in function.
                if (isset($this->funcs[$fnn])) {
                    $args = array();
                    // Collect all required args from the stack.
                    for ($i = 0; $i < $this->funcs[$fnn]['arguments']; $i++) {
                        if (is_null($op1 = $stack->pop())) {
                            return $this->trigger("function {$fnn} missing argument {$i}");
                        }
                        $args[] = $op1;
                    }
                    // If func allows additional args, collect them too, stopping on a
                    // NULL arg.
                    if (!empty($this->funcs[$fnn]['max arguments'])) {
                        for (; $i < $this->funcs[$fnn]['max arguments']; $i++) {
                            $arg = $stack->pop();
                            if (!isset($arg)) {
                                break;
                            }
                            $args[] = $arg;
                        }
                    }
                    $stack->push(call_user_func_array($this->funcs[$fnn]['function'], array_reverse($args)));
                }
                elseif (isset($fnn, $this->userfuncs)) {
                    $args = array();
                    for ($i = count($this->userfuncs[$fnn]['args']) - 1; $i >= 0; $i--) {
                        $value = $stack->pop();
                        $args[$this->userfuncs[$fnn]['args'][$i]] = $value;
                        if (is_null($value)) {
                            return $this->trigger('internal error');
                        }
                    }
                    // yay... recursion!!!!
                    $stack->push($this->pfx($this->userfuncs[$fnn]['func'], $args));
                }
            }
            else {
                if (is_numeric($token) || $token[0] == '"') {
                    $stack->push($token);
                }
                elseif (array_key_exists($token, $this->vars)) {
                    $stack->push($this->vars[$token]);
                }
                elseif (array_key_exists($token, $vars)) {
                    $stack->push($vars[$token]);
                }
                else {
                    return $this->trigger("undefined variable '{$token}'");
                }
            }
        }
        // When we're out of tokens, the stack should have a single element, the
        // final result:
        if ($stack->count() !== 1) {
            return $this->trigger('internal error');
        }
        return $stack->pop();
    }
    
    /**
     * Trigger an error, but nicely, if need be.
     *
     * @param string $msg
     *   Message to add to trigger error.
     *
     * @return bool
     *   Can trigger error, then returns FALSE.
     */
    protected function trigger($msg) {
        $this->errors[] = $msg;
        $this->last_error = $msg;
        if (!$this->suppress_errors) {
            trigger_error($msg, E_USER_WARNING);
        }
        return FALSE;
    }

}

/**
 * Class implementing a simple stack structure, used by ctools_math_expr.
 */
class ctools_math_expr_stack {
    
    /**
     * The stack.
     *
     * @var array
     */
    private $stack;
    
    /**
     * The stack pointer, points at the first empty space.
     *
     * @var int
     */
    private $count;
    
    /**
     * Ctools_math_expr_stack constructor.
     */
    public function __construct() {
        $this->stack = array();
        $this->count = 0;
    }
    
    /**
     * Push the value onto the stack.
     *
     * @param mixed $val
     */
    public function push($val) {
        $this->stack[$this->count] = $val;
        $this->count++;
    }
    
    /**
     * Remove the most recently pushed value and return it.
     *
     * @return mixed|null
     *   The most recently pushed value, or NULL if the stack was empty.
     */
    public function pop() {
        if ($this->count > 0) {
            $this->count--;
            return $this->stack[$this->count];
        }
        return NULL;
    }
    
    /**
     * "Peek" the stack, or Return a value from the stack without removing it.
     *
     * @param int $n
     *   Integer indicating which value to return. 1 is the topmost (i.e. the
     *   value that pop() would return), 2 indicates the next, 3 the third, etc.
     *
     * @return mixed|null
     *   A value pushed onto the stack at the nth position, or NULL if the stack
     *   was empty.
     */
    public function last($n = 1) {
        return !empty($this->stack[$this->count - $n]) ? $this->stack[$this->count - $n] : NULL;
    }
    
    /**
     * Return the number of items on the stack.
     *
     * @return int
     *   The number of items.
     */
    public function count() {
        return $this->count;
    }

}

/**
 * Helper function for evaluating 'if' condition.
 *
 * @param int $expr
 *   The expression to test: if <> 0 then the $if expression is returned.
 * @param mixed $if
 *   The expression returned if the condition is true.
 * @param mixed $else
 *   Optional. The expression returned if the expression is false.
 *
 * @return mixed|null
 *   The result. NULL is returned when an If condition is False and no Else
 *   expression is provided.
 */
function ctools_math_expr_if($expr, $if, $else = NULL) {
    return $expr ? $if : $else;
}

/**
 * Remove any non-digits so that numbers like $4,511.23 still work.
 *
 * It might be good for those using the 12,345.67 format, but is awful for
 * those using other conventions.
 * Use of the php 'intl' module might work here, if the correct locale can be
 * derived, but that seems unlikely to be true in all cases.
 *
 * @todo: locale could break this since in some locales that's $4.512,33 so
 * there needs to be a way to detect that and make it work properly.
 *
 * @param mixed $arg
 *   A number string with possible leading chars.
 *
 * @return mixed
 *   Returns a number string.
 */
function ctools_math_expr_number($arg) {
    // @todo: A really bad idea: It might be good for those using the 12,345.67
    // format, but is awful for those using other conventions.
    // $arg = preg_replace("/[^0-9\.]/", '', $arg);.
    return $arg;
}