gistfile1.scala

  def term: Parser[Expression] = factor ~ rep("*" ~ factor | "/" ~ factor) ^^ {
    case head ~ rest => {
      var result = head
      rest.foreach {
        case "*" ~ f => result = Multiply(result,f)
        case "/" ~ f => result = Divide(result,f)
      }

      result
    }
  }
  
  def expression: Parser[Expression] = term ~ rep( "+" ~ term | "-" ~ term) ^^ {
    case head ~ rest => {
      var result = head
      rest.foreach {
        case "+" ~ f => result = Add(result, f)
        case "-" ~ f => result = Subtract(result, f)
      }

      result
    }
  }

  def factor: Parser[Expression] =
    ( ignoreCase("true") ^^ (x => Literal(true))
      | ignoreCase("false") ^^ (x => Literal(false))
      | extract
      | function
      | identity~>parens(expression | entity)~>failure("unknown function")
      | coalesceFunc
      | nullableProperty
      | property
      | string ^^ (x => Literal(x))
      | number ^^ (x => Literal(x.toDouble))
      | parameter
      | entity
      | parens(expression)
      | failure("illegal start of value") )