Module StepByStep {
      Function PermutationStep (a) {
            c1=lambda (&f, a) ->{
                  =car(a)
                  f=true
            }
            m=len(a)
            c=c1
            while m>1 {
                  c1=lambda c2=c,p, m=(,) (&f, a) ->{
                        if len(m)=0 then m=a
                        =cons(car(m),c2(&f, cdr(m)))
                        if f then f=false:p++:  m=cons(cdr(m), car(m)) : if p=len(m) then p=0 : m=(,):: f=true
                  }
                  c=c1
                  m--
            }
            =lambda c, a (&f) -> {
                  =c(&f, a)
            }
      }
      k=false
      StepA=PermutationStep((1,2,3,4))
      while not k {
                 Print StepA(&k)
      }
      k=false
      StepA=PermutationStep((100,200,300))
      while not k {
                 Print StepA(&k)
      }
      k=false
      StepA=PermutationStep(("A", "B", "C", "D"))
      while not k {
                 Print StepA(&k)
      }
      k=false
      StepA=PermutationStep(("DOG", "CAT", "BAT"))
      while not k {
                 Print StepA(&k)
      }
}
StepByStep