def for_(cond, cb, val):
   if cond(val): return while_(cond, cb, cb(val))
   else: return val
 
 def fact(n):
   return for_( (lambda x: x[1] > 1),
                  (  lambda val: ( (val[0]*( val[1]-1 ) ), val[1]-1 )  )
                )[0]