Very Simple F# Compiler (Part 2 Revisited)

Just a quick note today to say that I have done about 30 seconds reading of some F# documentation and found out that reference cells can indeed be used in closures while local mutable values cannot. As it is a trivial exercise to re-write my character source to use local reference cells rather that global mutable values I have done so. Below is the updated code - I've also been able to remove those globals from my program.

  1 let getNextCharFromString (source : string) =
  2     let sourceList = ref (List.ofSeq source)
  3     let endOfString = ref (false)
  4     fun () ->
  5         match (!sourceList, !endOfString) with
  6             | _, true -> failwith "Past End of String"
  7             | [], _ ->
  8                 endOfString := true
  9                 char 0
 10             | h :: t, _ ->
 11                 sourceList := t
 12                 h