Is it possible to have an `is_module` function?

[Devon Estes]

We just encountered something that seemed kind of odd, so I wanted to pass it by the list to see if it could be a possible feature.

In Benchee we want to accept either a module or a function as an argument to a function. We'll have different behavior depending on the type there (since we're expecting any module passed in to implement a certain behaviour). However, there's no check for `is_module`. We were thinking of using `is_atom` (see here: https://github.com/PragTob/benchee/pull/148/files#diff-e8ef07ff6be58cfaaaf6f03420fc53e7R75), but that seems sort of confusing to me. I know technically modules are atoms, but would it be possible to have an `is_module` function that can be used in guard clauses and elsewhere that would more accurately convey the sort of thing we're trying to do?

[Martin Svalin]

The closest thing we have is `Code.ensure_loaded/1`. If you don't check that the module exists, you're basically just checking that the input is an atom. And if you use ensure_loaded, you'll have a predicate function with side effects. You'd also break the expectation of guard safety with the `is_` prefix.

Would your `is_module/1` have different behaviour than `is_atom/1`? Would it be true only of atoms of the form `:"Elixir.SomeModule"`? I'm not sure it should, since `defmodule :random_atom` is valid.

Which is a long way of saying, I think you should use `is_atom`. Perhaps with a line comment `# for modules`.

mån 16 okt. 2017 kl 20:02 skrev Devon Estes <devon....@gmail.com>:

We just encountered something that seemed kind of odd, so I wanted to pass it by the list to see if it could be a possible feature.

In Benchee we want to accept either a module or a function as an argument to a function. We'll have different behavior depending on the type there (since we're expecting any module passed in to implement a certain behaviour). However, there's no check for `is_module`. We were thinking of using `is_atom` (see here: https://github.com/PragTob/benchee/pull/148/files#diff-e8ef07ff6be58cfaaaf6f03420fc53e7R75), but that seems sort of confusing to me. I know technically modules are atoms, but would it be possible to have an `is_module` function that can be used in guard clauses and elsewhere that would more accurately convey the sort of thing we're trying to do?

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[Allen Madsen]

This is the best way I know how to determine if it's a module vs an atom.

function_exported?(X, :__info__, 1)

You won't be able to use it in a guard though.

Allen Madsen
http://www.allenmadsen.com

On Mon, Oct 16, 2017 at 3:10 PM, Martin Svalin <martin...@gmail.com> wrote:

The closest thing we have is `Code.ensure_loaded/1`. If you don't check that the module exists, you're basically just checking that the input is an atom. And if you use ensure_loaded, you'll have a predicate function with side effects. You'd also break the expectation of guard safety with the `is_` prefix.

Would your `is_module/1` have different behaviour than `is_atom/1`? Would it be true only of atoms of the form `:"Elixir.SomeModule"`? I'm not sure it should, since `defmodule :random_atom` is valid.

Which is a long way of saying, I think you should use `is_atom`. Perhaps with a line comment `# for modules`.

mån 16 okt. 2017 kl 20:02 skrev Devon Estes <devon....@gmail.com>:

We just encountered something that seemed kind of odd, so I wanted to pass it by the list to see if it could be a possible feature.

In Benchee we want to accept either a module or a function as an argument to a function. We'll have different behavior depending on the type there (since we're expecting any module passed in to implement a certain behaviour). However, there's no check for `is_module`. We were thinking of using `is_atom` (see here: https://github.com/PragTob/benchee/pull/148/files#diff-e8ef07ff6be58cfaaaf6f03420fc53e7R75), but that seems sort of confusing to me. I know technically modules are atoms, but would it be possible to have an `is_module` function that can be used in guard clauses and elsewhere that would more accurately convey the sort of thing we're trying to do?

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[José Valim]

function_exported?/3 returns false if the module is not loaded (i.e. it does not load the module). Code.ensure_loaded?/1 should be preferred but it is a very expensive operation to be allowed in guard.

The is_atom check is the way to go.

José Valim

www.plataformatec.com.br

Founder and 

Director of R&D

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