Hi,

I am trying to define a macro with 3 arguments (name, var, body) which is to generate function name/1
a) with argument var, possibly arbitrary complex pattern-matching expression
b) besides var, other variables bound in the outer scope can be used in the body

Example:

defmodule Mac3Use do
  import Mac3
  for {g, v} <- [g1: 1, g2: 2] do 
    gen String.to_atom("#{g}_x"), a,           do: {:ok, 1, a}
    gen String.to_atom("#{g}_y"), %{y: y} = a, do: {:ok, y, a}
  # gen String.to_atom("#{g}_z"), a,           do: {:ok, v, a} # undefined function v/0
  end
end

Below the implementation satisfying a). With slight modification it can handle guards. Unfortunately it doesn’t handle b) - I get “undefined function v/0” CompileError.

defmodule Mac3 do
  defmacro gen(name, var \\ quote(do: _), do: block) do
    var = Macro.escape(var)
    block = Macro.escape(block)
    quote bind_quoted: [name: name, var: var, block: block] do
      def unquote(name)(unquote(var)) do
        unquote(block)
      end
    end
  end
end

I was trying to modify this code without luck. Inspect of binding() inside quote shows g and v variables from the example with proper values bound, but unquote(block) doesn’t want to consume v.

Just a moment ago I checked that

    @v  v
    gen String.to_atom("#{g}_z"), a, do: {:ok, @v, a}

works, but it’s rather a hack.

As you could notice, the macro resembles ExUnit.Case.test/3, and its implementation is simplified version of that from ExUnit.

Is there an easy solution to this?

Thank you,
Waldemar.