Hi,

I’ve written the following to debug function calls, not sure if it’s useful for anyone else, and if so should I put it somewhere?

iex(1)> require Debug; import Debug
Debug

iex(2)> inspect_call(round(2.3*4.5))
round(10.35) -> 10

iex(3)> inspect_call(inspect({:foo, 1+2}))
inspect({:foo, 3}) -> "{:foo, 3}"
"{:foo, 3}"

iex(4)> inspect_call(IO.inspect(1) + IO.inspect(2))
1
2
+(1, 2) -> 3
3

It’s hopefully a fairly easily understandable piece of macro, though only evaluating the arguments once did make it more complicated. The first pattern-matching is taken from the Macro.decompose_call/1 function.

defmodule Debug do
  defmacro inspect_call(block) do
    {name, args, rebuild} =
      case block do
        {:{}, _metadata_a, args} when is_list(args) ->
          raise CompileError,
            description: "Using inspect_call on a map literal is not supported",
            file: __CALLER__.file,
            line: __CALLER__.line

        {{:., metadata_a, [remote, function]}, metadata_b, args}
        when is_tuple(remote) or is_atom(remote) ->
          {
            Macro.to_string({{:., metadata_a, [remote, function]}, [no_parens: true], []}),
            args,
            fn new_args -> {{:., metadata_a, [remote, function]}, metadata_b, new_args} end
          }

        {name, metadata_a, args} when is_atom(name) and is_atom(args) ->
          {to_string(name), [], fn _new_args -> {name, metadata_a, args} end}

        {name, metadata_a, args} when is_atom(name) and is_list(args) ->
          {to_string(name), args, fn new_args -> {name, metadata_a, new_args} end}

        _ ->
          raise CompileError,
            description:
              "Cannot understand function call #{Macro.to_string(block)}",
            file: __CALLER__.file,
            line: __CALLER__.line
      end

    eval_args =
      for n <- 1..length(args) do
        Macro.unique_var(:"eval_arg_#{n}", __MODULE__)
      end

    return_value = Macro.unique_var(:return_value, __MODULE__)

    quote do
      unquote_splicing(
        for {e_a, a} <- Enum.zip(eval_args, args) do
          quote do
            unquote(e_a) = unquote(a)
          end
        end
      )

      IO.write(
        unquote(name) <>
          "(" <>
          (unquote(eval_args)
           |> Enum.map(&inspect/1)
           |> Enum.join(", ")) <>
          ")"
      )

      unquote(return_value) = unquote(rebuild.(eval_args))

      IO.puts(" -> " <> inspect(unquote(return_value)))

      unquote(return_value)
    end
  end
end