Module aliasing in macros

Questions & Help Questions
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2

Hi,

I pursued my investigations further, and modified the Foo.show/1 function as follow.

defmodule Foo do
    defmacro show(frag = {:__aliases__, _, refs}) do
        resolved = Macro.expand(frag, __CALLER__)
        IO.puts """
        Alias
        frag \t #{inspect frag}
        resolved #{inspect resolved}
        """
        frag
    end

    defmacro show(frag = {{:., _, [path, target]}, _, _}) do
        resolved = Macro.expand(path, __CALLER__)
        IO.puts """
        Call
        path \t #{inspect path}
        resolved #{inspect resolved}#{inspect target}
        """
        frag
    end
end

Basically I catch fragments bearing aliasing information to make some experiments.

Here is the output

Alias
frag     {:__aliases__, [counter: 0, line: 38], [:A]}
resolved Outer

Alias
frag     {:__aliases__, [counter: 0, line: 39], [:B]}
resolved Outer.Inner

Alias
frag     {:__aliases__, [counter: 0, line: 40], [:C]}
resolved Outer.Inner

Call
path     {:__aliases__, [counter: 0, line: 41], [:C]}
resolved Outer.Inner:foo

ast {:__aliases__, [alias: Outer], [:A]}

We can see that, though fragments do not bear aliasing information, Macro.expand resolves aliases at compile time.

Cheers

Nicolas -

P.S. The question may rise of knowing WHY I needed to have those resolved symbols. Well, I wanted to be able to take some decisions based on the knowledge that a function is exported by a certain module … it proved to be a wrong way, but the underlying purely technical is still interesting :slight_smile: