procedure main(A)
   \A := ["cat","hat",7]
   x := history()
   every x.set(!A)
   write("x current value is: ",x.val())
   write("Number of saved values is: ",x.size())
   writes("3 most recent x values from newest to oldest: ")
   every writes(" ",x.gen()\3)
   write()
   while write("x value was: ",\x.get())
   write("Number of saved values is now: ",x.size())
end

class history(x)
   method size(); return *x; end
   method val();  return x[-1]; end
   method set(v); put(x,v); end
   method get();  return pull(x); end
   method gen();  suspend x[*x to 1 by -1]; end
initially
   x := []
end