I was hoping I could get something like this working: defmodule FooRegistry do @foos [ FirstFoo, SecondFoo, ThirdFoo ] @foos_by_another_name Enum.into(foos, %{}, fn foo -> {foo.another_name(), foo} end) @type foo [Enum.map(@foos, fn foo -> foo.t end)] @spec list_foos() ::…

I guess the type declaration would somehow need to actually be separated by | so that Enum.map would naturally not work.

@zachdaniel : You need to write helper module with some macros and then call them to generate ast for special module attributes like @type. For @type you need to return ast in format: # root element in case @foos count greater than 2: { :|, [], children } # root element in case @foos count is…

Woah. Thanks for the tip! I wonder if people would wnat to do this more often if it was provided by dialyzer. @type foo :: @foos.t for shorthand or something. I’ll look into implementing something like this. Thanks!

For posterity: defmodule Test do @keys ~w(a b c)a @type key :: unquote(Enum.reduce(@keys, &{:|, [], [&1, &2]})) end

Is there a way to wrap that in a macro, ex. union_type/1, so that one could write: @type key :: union_type(@keys) I haven’t been able to figure out how to write such a macro. This is the best I’ve been able to do so far: defmodule UnionType do def union_type_ast(literals) do literals |>…

[image] kenny-evitt: defmodule UnionType do def union_type_ast(literals) do literals |> Enum.reverse() |> Enum.reduce(&{:|, [], [&1, &2]}) end end First of all instead of reverse + reduce (2 iterations) you should use [head | tail] (1 iteration) like: defmodule Example do …

Thanks @Eiji ! I like your recursive definition but I’m not sure it’s much clearer – it doesn’t seem particularly sensible to support a single type for a ‘union type’ macro. Avoiding two iterations tho is pretty nice! And the function could always be made private anyways. I suspected that it would …

[image] kenny-evitt: Is there a way to wrap that in a macro, ex. union_type/1 , so that one could write: @type key :: union_type(@keys) In both @spec and @type you need to wrap everything in unquote call. Without that instead of calling function/macro the AST of such call would be stored: i…

[image] Eiji: In both @spec and @type you need to wrap everything in unquote call. That’s the conclusion I tentatively had reached myself but do you know why exactly this is? I’d guess it has to do with the details of how, and when, the compiler parses the @spec and @type declarations, but I …

[image] kenny-evitt: What’s your personal preference for doing this kind of thing? Do you not do anything like this in your own code? Depends on situation … in private API I would use just unquote call in @spec for simplicity. However in order to create a nice public API I would write a simpl…

Dynamically generate typespecs from module attribute list

Questions & Help Questions

kenny-evitt February 2, 2025, 11:03pm 18

I just checked out the library

Dreams of transclusion in Xanadu