Is this explanation of &1 + &2 + &1 correct?

[Dave Thomas]

You have to be careful when using the `&1` notation—when Elixir sees

it, in converts the immediately enclosing expression into a

function. So, the following works:

iex> func = &1 + &2

#Function<erl_eval.12.82930912>

iex> func.(9, 4)

13

However, this doesn't.

iex> func = &1 + &2 + &1

#Function<erl_eval.12.82930912>

iex> func.(9, 4)

** (BadArityError) bad arity error: #Function<erl_eval.6.82930912> 

   called with [3,4]

That's because `&1 + &2 + &1` is parsed internally as `(&1 + &2) +

&1`. The parenthesized part is self-contained, so Elixir converts it

to 

(fn a, b -> a+b end) + &1

Now it continues to parse the line, sees the second `&1` and generates

a second anonymous function, enclosing the whole expression:

fn x -> (fn a, b -> a+b end) + x end

When we call this with two parameters, it raises a bad arity error,

because the outer function only expects one.

[José Valim]

Yes, this is perfect.

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José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Lead Developer