Hi there, I am currently learning Elixir by going through the Mix and OTP guide on elixir-lang.org . I have read through the Getting Started guide already. I am having trouble getting my head around the use of placeholder arguments when capturing and partially applying named functions. The specific…

It is the state of the Agent that get passed to the anonymous function.

Hello and welcome, & is a shortcut for defining anonymous function, and &1, &2… are the parameters to this function. &Map.get(&1, key) # is equal to fn x -> Map.get(x, key) end You might find version with two parameters, in particular with reduce… For example. iex> Enum.reduce [1, 2, 3], & &1…

Hello kokolegorille, Thanks for your reply and the explanation of how the ampersand & works. In general, it makes sense to me, like in the following example: iex> fun = &(&1 + 1) #Function<6.71889879/1 in :erl_eval.expr/5> iex> fun.(1) 2 I have no problems with that. However, I am still confused…

The state of the agent? Can you please elaborate?

An agent store some state… Agent — Elixir v1.20.2

Oh! Now I see. The &1 is the Agent’s state, which is being passed from the Agent to the anonymous function. Maybe its just me, but that seems to be a quite different behaviour for the &1 than it had in the other examples.

[image] timbot: Maybe its just me, but that seems to be a quite different behaviour for the &1 than it had in the other examples. There is nothing magic about how &1 is working here. Rather, it’s the Agent.get function that is doing the work. &Map.get(&1, key) is just an anonymous function th…

That is the power of function as first class citizen, You can pass the implementation as an argument :slight_smile:

The capture operator is just a different way to write anonymous functions, but it is perfectly equivalent to the fn ... -> ... end form. The &1, &2, etc. are nothing else that the first argument, the second argument, etc.: # This: fun = fn a, b -> a + b end # Is the same as this: fun = &(&1 + &2…

Thanks for the explanations, folks. I have added a pull request to the documentation over at Github adding a clarifying sentence about this behavior of the Agent.

Partially applied functions and placeholder arguments

Questions & Help Questions

kokolegorille April 11, 2020, 12:02pm 6

An agent store some state…