[php] "call to undefined function" error when calling class method

this is the error Fatal error: Call to undefined function assign(
this is the code, as you can see i obviously have defined the function so why is it not working

class shades {
    function create($name, $shades, $slug, $shortDesc, $longDesc, $position){
        $name = sanitize_paranoid_string($name);
        $slug = slug($name);
        $shortDesc = sanitize_sql_string($shortDesc);
        $longDesc = sanitize_sql_string($longDesc);
        $query = mysql_query("INSERT INTO products (type, name, slug, shortDesc, htmlDesc, position)VALUES('shades','$name','$slug','$shortDesc','$longDesc','$position')")or die(mysql_error());  
        $ID = mysql_insert_id();
        assign($shades, $ID);
        if($query) {return true;}
        else {return false;};
    }
    function delassign($toID){
        mysql_query("DELETE FROM assign WHERE type='shades' AND toID='$toID'")or die(mysql_error());    
    }
    function assign($shades, $toID)
    {
        foreach($shades as $shade)
        {
            $result = mysql_query("INSERT INTO assign(type, typeID, toID)VALUES('shades','$shade','$toID')")or die(mysql_error());
            if($result){echo "Added!";}
            else{echo"Not Added!";}
        };  
    }
}

Mates,

I stumbled upon this error today while testing a simple script. I am not using "class" function though so it take it with grain of salt. I was calling function before its definition & declaration ...something like this

      try{
             foo();
         }
       catch (exception $e)
           {
            echo "$e->getMessage()";
           }

       function foo(){
                       echo "blah blah blah";
                     }

so php was throwing me error "call to undefined function ".

This kinda seem classic programming error but may help someone in need of clue.

you need to call the function like this

$this->assign()

instead of just assign()

Another silly mistake you can do is copy recursive function from non class environment to class and don`t change inner self calls to $this->method_name()

i`m writing this because couldn`t understand why i got this error and this thread is first in google when you search for this error.