anchor.diff:  //[<Struct>]
   type State={
       c:NFAState
  -    out:State option
  -    out1:State option
  +    mutable out:State option
  +    mutable out1:State option
       mutable lastList:int
   }
   type RegexState(matchstate:State,nstate:int)=
  
positive.code:     let s = {lastList=0;c=c;out=out;out1=out1}
      s
  
  type Ptrlist= State option list 
  
  (*
   * A partially built NFA without the matching state filled in.
   * Frag.start points at the start state.
  
negative.code:         | '.' -> //catenate 
              let e2 = pop()
              let e1 = pop()
              patch(e1.out, e2.start)
              push(frag(e1.start, e2.out))
          | '|' -> //alternate
              let e2 = pop()
  