traverse

defmodule Traverse.Tools do
  use Traverse.Types

  @doc """
  Utility to trace your traversals by passing your traversal function to this trace_wrapper.

  Instead of passing `f` you can pass `make_trace_fn(f)` as long as f is of the correct type.

  This wrapper will trace the actual arguments and the return value to stderr.
  """

  @spec make_trace_fn(t_traceable_fn) :: t_traceable_fn
  def make_trace_fn(fun)

  def make_trace_fn(fun) when is_function(fun, 1) do
    with f <- fn e ->
           IO.puts(:stderr, ">>> #{inspect(e)}")
           r = fun.(e)
           IO.puts(:stderr, "<<< #{inspect(r)}")
           r
         end,
         do: f
  end

  def make_trace_fn(fun) when is_function(fun, 2) do
    with f <- fn e, a ->
           IO.puts(:stderr, ">>> #{inspect(e)}, #{inspect(a)}")
           r = fun.(e, a)
           IO.puts(:stderr, "<<< #{inspect(r)}")
           r
         end,
         do: f
  end

  def make_trace_fn(fun) when is_function(fun, 3) do
    with f <- fn e, a1, a2 ->
           IO.puts(:stderr, ">>> #{inspect(e)}, #{inspect(a1)}, #{inspect(a2)}")
           r = fun.(e, a1, a2)
           IO.puts(:stderr, "<<< #{inspect(r)}")
           r
         end,
         do: f
  end
end