I can do: if true, do: :foo, else: :bar and: if true do :foo else :bar end And I can do: for i <- 0..3, do: {i, i+i}, into: %{} but not: for i <- 0..3 do {i, i+i} into %{} end :thinking: why is that?

Because else got special treatment to ease user experience. This sugar is not available for any other atom outside the small set of predefined ones (else, rescue, catch, and after).

You can, you have to pass them before the do. for …, into: %{} do … end

if true, do: :foo, else: :bar and: if true do :foo else :bar end are different, although they look similar. The first form is actually a if macro accepting two arguments. if(true, [do: :foo, else: :bar]) And to make the second form works, we need a into macro which I don’t think we have it…

[image] chungwong: are different, although they look similar. That is not true. Both are exactly the same thing for the compiler: iex(1)> quote do ...(1)> if true do ...(1)> :foo ...(1)> else ...(1)> :bar ...(1)> end ...(1)> end {:if, [context: Elixir, import: Kernel], [true, [do: :foo, …

Yes they are the same. A do block after a call adds the [do: ...] argument to the function/macro call on the left. So if you call this (notice the parentheses for the if call) if(a == 1) do :ok end The compiler kind of rewrites it to if(a == 1, [do: :ok]) This works for functions too: defmodu…

Well, no. It is still consistent behaviour among all other calls: quote do foo bar: 1, do: 10 end # => {:foo, [], [[bar: 1, do: 10]]} quote do foo bar: 1 do 10 end end # => {:foo, [], [[bar: 1], [do: 10]]} There are 2 reasons why for is special form and not “regular” macro: Compiler n…

I don’t understand to what you say “no”. I mean in your example it calls two different foo functions. The for construct handles that in a special way, there are not several definitions for for to my knowledge in the Elixir code.

As I said, it is literally impossible to define for in Elixir. I meant that do: 10 and do … end aren’t really treated differently just for for, but the same rules applies to all calls. for is special form not because of do but because each x <- y is separate argument, so for i <- 1..10, do: i is 2-…

Ok so it is not defined as a special form just for the arity problem, but otherwise it is just what I said, basically it is a special form because it requires special treatment at the compiler level.

Elixir Programming Language Forum

Comprehension syntax

Questions & Help Questions

Sebb October 13, 2021, 8:51pm 3

So I can’t use into, uniq, reduce in a for ... end block?