predicatebuilder - LinqPad Predicatebuider Expression call not working -

i trying examples working found @ http://www.albahari.com/nutshell/predicatebuilder.aspx

i have following code:

 public partial class pricelist          {         public string name { get; set; }         public string desc {get;set;}         public datetime? validfrom {get;set;}         public datetime? validto{get;set;}          public static expression> iscurrent()         {         return p => (p.validfrom == null || p.validfrom <= datetime.now) && (p.validto == null || p.validto >= datetime.now);         }          }       void main()     {         list pllist = new list()         {         new pricelist(){ name="billy", desc="skilled", validfrom = datetime.now.adddays(-10.0) , validto= datetime.now.adddays(1.0) },         new pricelist(){ name="jamie", desc="quick study",validfrom =datetime.now.adddays(-10.0) , validto= datetime.now.adddays(1.0) },         new pricelist(){name= "larry", desc= "rookie",validfrom = datetime.now.adddays(-10.0) , validto= datetime.now.adddays(1.0) }         };       // method 1      var myresultlist = pllist.where ( p => (p.validfrom == null || p.validfrom <= datetime.now)       && (p.validto == null || p.validto >= datetime.now)).dump();      // method 2          pllist.where(pricelist.iscurrent()).dump(); // not work       }  

my question between method 1 , method 2, iscurrent() method not work functionality of code identical, when call method 2 pricelist.iscurrent() following error.

any suggestions appreciated.

'system.collections.generic.list' not contain definition 'where' , best extension method overload 'system.linq.queryable.where(system.linq.iqueryable, system.linq.expressions.expression>)' has invalid arguments  instance argument: cannot convert 'system.collections.generic.list' 'system.linq.iqueryable' 

try

   pllist.asqueryable().where(pricelist.iscurrent()).dump();   

ps, example doesn't compile, i'm guessing mean

public static expression<func<pricelist, bool>> iscurrent() { ... 

and

list<pricelist> pllist = new list<pricelist>() ...