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-ary function and for i <- 1..10, j <- 1..10, do: i + j is 3-ary function. So either for would need to have N different heads and just fail in case if someone would like to use more than that, then it would fail (see older Rust compilers to see that problem, there Debug is defined only up to 32-ary tuples, as there is no variadic generics). Due that problem for and with must be defined as special forms, because they require parser magic to be then expanded properly.
