{ let
  { Fact = -- compile-time constant binding
    { proc { N } as -- precondition: N.IsI48[] & (N >= 0)
    : var { Res = 1 } in -- variable binding
    : do Res after -- return result
    : while N <> 0 do -- loop while N does not equal to zero
      Res = N * Res; N = N - 1
    }
  }
  in -- use Fact here or just make the whole expression to evaluate to it:
  Fact
}