diff --git a/Formula1.php b/Formula1.php
index 5a15474..e465499 100644
--- a/Formula1.php
+++ b/Formula1.php
@@ -6,17 +6,25 @@ class Formula1 {
 	private $dual_hp_ops = ['/','*','%','^'];
 	private $dual_lp_ops = ['+','-'];
 	private $single_ops = ['+','-'];
+	private $functions =   ['abs','acos','acosh','asin','asinh','atan','atanh','ceil',
+							'cos','cosh','deg2rad','exp','expm1','floor','getrandmax',
+							'lcg_value','log10','log1p','log',
+							'mt_getrandmax','mt_rand','pi','rad2deg','rand','round',
+							'sin','sinh','sqrt','tan','tanh'];
 
 	public function __construct($formula, $params=[], $precision=null, $precision_mode=PHP_ROUND_HALF_UP) {
 		$this->params = $params;
 		$this->precision = $precision;
 		$this->precision_mode = $precision_mode;
 		$f = $this->replace_parenth($formula, 0);
-		if(strrpos($f, ')')>-1) {
-			$this->parse_error = 'PARSING ERROR: Too many closing parenthesis !';
-			return(false);
+		if($this->parse_error == ''){
+			if(substr_count(')',$f) > substr_count('(',$f) ) {
+				$this->parse_error = 'PARSING ERROR: Too many closing parenthesis !';
+			} else if(substr_count(')',$f) < substr_count('(',$f) ) {
+				$this->parse_error = 'PARSING ERROR: Too many opening parenthesis !';
+			}
+			$this->tree = $this->parse($f);			
 		}
-		$this->tree = $this->parse($f);
 	}
 
 	private function do_single_op($op, $x){
@@ -26,6 +34,41 @@ class Formula1 {
 		}
 	}
 
+	private function do_function($fn, $x){
+		switch($fn){
+			case 'abs': return(abs($x));
+			case 'acos': return(acos($x));
+			case 'acosh': return(acosh($x));
+			case 'asin': return(asin($x));
+			case 'asinh': return(asinh($x));
+			case 'atan': return(atan($x));
+			case 'atanh': return(atanh($x));
+			case 'ceil': return(ceil($x));
+			case 'cos': return(cos($x));
+			case 'cosh': return(cosh($x));
+			case 'deg2rad': return(deg2rad($x));
+			case 'exp': return(exp($x));
+			case 'expm1': return(expm1($x));
+			case 'floor': return(floor($x));
+			case 'getrandmax': return(getrandmax());
+			case 'lcg_value': return(lcg_value($x));
+			case 'log10': return(log10($x));
+			case 'log1p': return(log1p($x));
+			case 'log': return(log($x));
+			case 'mt_getrandmax': return(mt_getrandmax());
+			case 'mt_rand': if($x!='') return(mt_rand(0,$x)); else return(mt_rand());
+			case 'pi': return(pi());
+			case 'rad2deg': return(rad2deg($x));
+			case 'rand': if($x!='') return(rand(0,$x)); else return(rand());
+			case 'round': return(round($x));
+			case 'sin': return(sin($x));
+			case 'sinh': return(sinh($x));
+			case 'sqrt': return(sqrt($x));
+			case 'tan': return(tan($x));
+			case 'tanh': return(tanh($x));
+		}
+	}
+
 	private function do_dual_op($x, $op, $y){
 		switch($op){
 			case '+': return($x+$y);
@@ -54,9 +97,14 @@ class Formula1 {
 	private function replace_parenth($f, $expr_index){
 		$allops = array_merge($this->dual_lp_ops, $this->dual_hp_ops, $this->single_ops);
 		$nf='';
+		$last_op_idx = -1;
 		for($i=0;$i<strlen($f);$i++) {
 			$c = substr($f,$i,1);
 			if($c=='(') {
+				if( ($i>$last_op_idx+1) && (!in_array(substr($f,$last_op_idx+1,$i-$last_op_idx-1), $this->functions)) ) {
+						$this->parse_error = "PARSING ERROR: Unknown function (".substr($f,$last_op_idx+1,$i-$last_op_idx-1).") !";
+						return('');						
+				}
 				$closing_idx = $this->find_closingp($f, $i);
 				if($closing_idx===false) {
 					$this->parse_error = "PARSING ERROR: missing closing parenthesis !";
@@ -64,10 +112,15 @@ class Formula1 {
 				}
 				$expr = substr($f, $i+1, $closing_idx-$i-1);
 				$expr_name = 'expr_'.$expr_index++;
-				$nf.=$expr_name;
+				if($i>$last_op_idx+1) { //functions : keep parenthesis
+					$nf.='('.$expr_name.')';
+				} else { // expression: remove parenthesis
+					$nf.=$expr_name;
+				}
 				$this->params[$expr_name] = $this->replace_parenth($expr, $expr_index);
 				$i =  $closing_idx; // let the loop do the +1
 			} else {
+				if(in_array($c, $allops)) $last_op_idx=$i;
 				$nf .= $c;
 			}
 		}
@@ -76,7 +129,6 @@ class Formula1 {
 
 
 	private function parse($f){	
-//echo('<div style="font-size:12px;color:blue;">Parsing:'.$f.'</div>');		
 		$re = '/^(.+?)([\\'.implode('\\',$this->dual_lp_ops).'])(.+)$/'; // dual low priority op
 		if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
 			$recur = $this->parse($matches[3][0]);
@@ -94,33 +146,24 @@ class Formula1 {
 					$recur = $this->parse($matches[2][0]);
 					if($recur!==false) return([null, $matches[1][0], $recur]);
 					else return(false);
-				} else {
-					$re1 = '/^([A-Za-z][A-Za-z0-9_]*)\[\"([A-Za-z0-9_]+)\"\]$/'; // arrays with alphanum keys
-					$re2 = "/^([A-Za-z][A-Za-z0-9_]*)\[\'([A-Za-z0-9_]+)\'\]$/"; // arrays with alphanum keys
-					if(preg_match($re1, $f, $matches1, PREG_OFFSET_CAPTURE, 0)||preg_match($re2, $f, $matches2, PREG_OFFSET_CAPTURE, 0)){ 
-						$array_name = (count($matches1)>0) ? $matches1[1][0] : $matches2[1][0];
-						$array_key = (count($matches1)>0) ? $matches1[2][0] : $matches2[2][0];
-						if(array_key_exists($array_name, $this->params) && is_array($this->params[$array_name])) {
-							if(array_key_exists($array_key, $this->params[$array_name])) {
-								return($this->parse($this->params[$array_name][$array_key]));
-							} else {
-								$this->parse_error = 'PARSING ERROR: Unknown key "'.$array_key.'" for array "'.$array_name.'" ';
-								return(false);
-							}
-						} else {
-							$this->parse_error = 'PARSING ERROR: Unknown array "'.$array_name.'" ';
-							return(false);
-						}
+				} else {				
+					$re = '/^'.implode('|', array_map(function($e){ return($e.'\((.*)\)'); }, $this->functions) ).'$/'; // functions
+					if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
+						$j=-1; for($i=1;$i<count($matches);$i++){ if($matches[$i][1]>-1) { $j=$i; break; } };
+						$recur = $this->parse($matches[$j][0]);
+						if($recur!==false) return([null, $this->functions[$j-1], $recur]);
+						else return(false);
 					} else {
-						$re = '/^([A-Za-z][A-Za-z0-9_]*)\[(\d+)\]$/'; // arrays with alphanum keys
-						if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-							$array_name = $matches[1][0];
-							$array_index = $matches[2][0];
+						$re1 = '/^([A-Za-z][A-Za-z0-9_]*)\[\"([A-Za-z0-9_]+)\"\]$/'; // arrays with alphanum keys
+						$re2 = "/^([A-Za-z][A-Za-z0-9_]*)\[\'([A-Za-z0-9_]+)\'\]$/"; // arrays with alphanum keys
+						if(preg_match($re1, $f, $matches1, PREG_OFFSET_CAPTURE, 0)||preg_match($re2, $f, $matches2, PREG_OFFSET_CAPTURE, 0)){ 
+							$array_name = (count($matches1)>0) ? $matches1[1][0] : $matches2[1][0];
+							$array_key = (count($matches1)>0) ? $matches1[2][0] : $matches2[2][0];
 							if(array_key_exists($array_name, $this->params) && is_array($this->params[$array_name])) {
-								if(isset($this->params[$array_name][$array_index])) {
-									return($this->parse($this->params[$array_name][$array_index]));
+								if(array_key_exists($array_key, $this->params[$array_name])) {
+									return($this->parse($this->params[$array_name][$array_key]));
 								} else {
-									$this->parse_error = 'PARSING ERROR: Unknown index "'.$array_index.'" for array "'.$array_name.'" ';
+									$this->parse_error = 'PARSING ERROR: Unknown key "'.$array_key.'" for array "'.$array_name.'" ';
 									return(false);
 								}
 							} else {
@@ -128,20 +171,37 @@ class Formula1 {
 								return(false);
 							}
 						} else {
-							$re = '/^([A-Za-z][A-Za-z0-9_]*)$/'; // simple variables
+							$re = '/^([A-Za-z][A-Za-z0-9_]*)\[(\d+)\]$/'; // arrays with alphanum keys
 							if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-								if(array_key_exists($matches[0][0], $this->params)) return($this->parse($this->params[$matches[0][0]]));
-								else {
-									$this->parse_error = 'PARSING ERROR: Unknown expression "'.$matches[0][0].'" ';
+								$array_name = $matches[1][0];
+								$array_index = $matches[2][0];
+								if(array_key_exists($array_name, $this->params) && is_array($this->params[$array_name])) {
+									if(isset($this->params[$array_name][$array_index])) {
+										return($this->parse($this->params[$array_name][$array_index]));
+									} else {
+										$this->parse_error = 'PARSING ERROR: Unknown index "'.$array_index.'" for array "'.$array_name.'" ';
+										return(false);
+									}
+								} else {
+									$this->parse_error = 'PARSING ERROR: Unknown array "'.$array_name.'" ';
 									return(false);
 								}
-							} else {				
-								$re = '/^\d*(\.\d+)?$/'; // unsigned float or int
+							} else {
+								$re = '/^([A-Za-z][A-Za-z0-9_]*)$/'; // simple variables
 								if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
-									return($matches[0][0]);
-								} else {
-									$this->parse_error = 'PARSING ERROR at '.$f.'<br/>';
-									return(false);
+									if(array_key_exists($matches[0][0], $this->params)) return($this->parse($this->params[$matches[0][0]]));
+									else {
+										$this->parse_error = 'PARSING ERROR: Unknown expression "'.$matches[0][0].'" ';
+										return(false);
+									}
+								} else {				
+									$re = '/^\d*(\.\d+)?$/'; // unsigned float or int
+									if(preg_match($re, $f, $matches, PREG_OFFSET_CAPTURE, 0)){ 
+										return($matches[0][0]);
+									} else {
+										$this->parse_error = 'PARSING ERROR at '.$f.'<br/>';
+										return(false);
+									}
 								}
 							}
 						}
@@ -149,12 +209,15 @@ class Formula1 {
 				}
 			}
 		}
+
 	}
 
 	private function comp($t) {
 		if(!is_array($t)) return($t);
-		if($t[0]===null) { //unary op
-			return($this->do_single_op($t[1],$this->comp($t[2])));
+		if($t[0]===null) { // unary op or function
+			if(in_array($t[1], $this->single_ops)) return($this->do_single_op($t[1],$this->comp($t[2])));
+			if(in_array($t[1], $this->functions)) return($this->do_function($t[1],$this->comp($t[2])));
+			return(0); // Should not happen really cause error catched during parsing...
 		} else {
 			return($this->do_dual_op($this->comp($t[0]), $t[1],$this->comp($t[2])));
 		}