anchor.diff:  
     type expr = Nil
               | Boolean of bool
  -            | Number of decimal
  +            | Number of int
               | Symbol of string
  -            | Function of string * expr list
  +            | Call of string * expr list
  +            | Operator of operator_t
  +  and operator_t = delegate of expr list -> expr option
   
     module Expr =
       let ToBoolean e =
  
positive.code: 
      let private command expr =
        pstring "(" >>. spaces >>. symbol .>> spaces .>>. sepEndBy expr spaces .>> pstring ")"
        |>> fun (symbol, args) -> Function (symbol, args)
  
      let private expr =
        fix <| fun expr -> token <|> command expr
  
negative.code:     | Result.OK expr ->
        let engine = Orelang.Engine()
        printfn "result: %A" <| engine.Evaluate expr
  
    let testString s =
      printfn "\nstring: %s" s
  