Does Dialyzer analyze anonymous functions?

Question

In my progress of learning Elixir, I am playing around with Dialyzer to put types on my functions. In this regard, I've noticed that Dialyzer doesn't seem to check the types for anonymous functions.

In the example below, I am passing an anonymous function which adds two numbers and returns a number (t::number -> number), into the all? function. Thus I am not returning boolean as promised in the all? spec (t::any -> boolean).

defmodule Exercises do                                                                         
  @spec all?([t::any], (t::any -> boolean)) :: boolean                                         
  def all?([], _), do:  true                                                                   
  def all?([h|t], con) do                                                                      
    if con.(h) do                                                                              
      all?(t,con)                                                                              
    else                                                                                       
      false                                                                                    
    end                                                                                        
  end                                                                                          

  @spec funski() :: boolean                                                                    
  def funski() do                                                                              
    all?([1,1,2], &(&1 + 1))                                                                
  end
end

Dialyzer doesn't seem to report any errors or warnings for this code, and I am curios if Dialyzer is unable to check this kind of mistakes or if I am doing something wrong.

Crowfoot

Answer 1

It seems to be a Dialyzer bug. Calling :lists.all/2 (with the arguments swapped) produces the correct warning but for some reason calling your local all?/2 function with the same spec does not.

Cleaves

swapping the arguments of all?/2 makes Dialyzer yield following warning The call 'Elixir.Exercises':'all?'(fun((_) -> number()),[1 | 2,...]) will never return since the success typing is (maybe_improper_list(),any()) -> boolean() .... But I don't see how that relates to the analysis of the anonymous function &(&1 + 1) – Crowfoot

I meant that when calling :lists.all/2 (a completely different function) you should swap the arguments. And when calling that function you will get the correct warning. So it seems to be a bug in dialyzer that do not get the warning for your function. – Langmuir

ah sorry, I miss-read your answer. However, :list.all(&(&1 + 1), [1,1,2]) doesn't make Dialyzer yield any warnings when I add it instead of the all?([1,1,2]. &(&1 + 1)).. Maybe it has something to do with the generated .beam code produced by the elixir compiler which I am feeding Dialyzer with... – Crowfoot

:lists.all/2 warns for me. I recommend using this project for running dialyzer: github.com/fishcakez/dialyze – Langmuir

nice tool, thank you. Now I get the warning as well (still no warning for the initial problem of course). – Crowfoot