Dyn.groovy

def list=[1,"nan",new Whatever()] // neat!

def nan="nan"
def one=1
one+nan
"1nan"
one-nan
// No signature of method: java.lang.Integer.minus() is applicable for argument types: (java.lang.String)
Object nan2="nan2"
Object two=2
two+nan2==((Integer)two).plus((String)nan2)
//"2nan2"

Dyn.hs

module Dyn where

data Dyn=DynInt Int | DynStr String -- | all types you want
     deriving Show

plus (DynInt x) (DynInt y)=DynInt $ x+y
plus (DynStr x) (DynInt y)=DynStr $ x++(show y)
plus (DynInt x) (DynStr y)=DynStr $ (show x)++y

minus (DynInt x) (DynInt y)=DynInt $ x-y
minus (DynStr x) (DynInt y)=undefined -- ???
minus (DynInt x) (DynStr y)=undefined -- ???

dynaList :: [Dyn]
dynaList = [DynInt 1,DynStr "nan"]

dynamicGoodnessQMark = plus (DynInt 1) (DynStr "nan")
bang=minus (DynInt 3) (DynStr "nan")