One problem with our vehicle type is that the fuel is defined as a string, whereas it would be better to restrict the choice to set of values. Previously, we discussed a macro that provides one approach to enumerations. In the absence of a preferred definition in Julia, various developers have adopted different strategies and I'll provide our own here.

First, we will use a vector of type {Any} to hold the enumerated values. This could be consts using integers or strings, but I'll restrict it to a list of symbols and create the vnum.jl file to hold the following:

typealias VecAny Array{Any,1}
function vnum(syms::Symbol...)
  A = {}
  for v in syms
    push!(A,v)
  end
  A
end
function vidx(A::VecAny, a::Symbol)
  for (i, v) in enumerate(A)
    if v == a then
      return (i - 1)
    end
    nothing
  end
end
vin(A::VecAny, a::Symbol) = (vidx(A,a) >= 0 ? true : false)

vnum is created by pushing a variable list of symbols onto an empty Any vector. Additionally, there...