Elixir in Depth – Reading and personal notes

Re:Elixir in Depth – Reading and personal notes by randomstudent on Thursday August 17, 2017 @03:13PM (#15039899)

Yes.

Superficially, `do ... end` blocks look like English, because they are English words. On the other hand, they don't really correspond to any real grammar construct of the English language. They live in the the uncanny valley where you try to read it like English, but you can't actually read it as such. For some reason, the use of keywords like `def`, `defmodule` or `defmacro` doesn't bother me as much. Maybe because they are not block delimiters?

In my opinion, braces, delimiters or parenthesis create less visual noise than endless cascades of `end` keywords:

    def f(x) do
      ...        
          end
        end
      end
    end

There are other block keywords besides `end`, which serve no purpose other than simplify some keyword list arguments at the cost of higher complexity.

In general there is too much syntax sugar for things that don't really benefit from it.

Parenthesis in function calls are optional in some places but not others, which creates some unnecessary confusion.

The syntax for anonymous functions is

    fn arg -> do ... end

The `end` keyword is strange and I keep forgetting it (that's more a problem with me than the syntax, I know).

The language is subtly whitespace sensitive in some places, while being mostly whitespace insensitive.

Macros can't take a variable number of arguments, which leads to the proliferation of Special Forms (it's a kind of macros that is treated as special by the compiler) which could perfectly be macros if it weren't for this limitation.

For a situation where this causes problems and requires some extra weirdness in what should be a simple DSL, look at this Github issue in the new testing library scheduled for inclusion in the standard library: https://github.com/whatyouhide/stream_data/issues/21

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Re:Elixir in Depth – Reading and personal notes by josevalim on Thursday August 17, 2017 @05:02PM (#15040977)

> Macros can't take a variable number of arguments, which leads to the proliferation of Special Forms which could perfectly be macros if it weren't for this limitation.

This is not true.

We have only two variadic special forms: "for" and "with".

"for" needs to be implemented as a special form as it emits some optimizations that are only available at the Core Erlang level.

"with" needs to be implemented as a special form as it has different lexical properties than a bunch of nested cases.

None of those could be implemented with macros.

Regarding whitespace sensitiveness, most languages have subtle issues, to varying degrees but especially if you have optional line terminators. Although it is true one or two extra cases appear in Elixir due to optional parentheses.

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Re:Elixir in Depth – Reading and personal notes by randomstudent on Friday August 18, 2017 @08:07AM (#15045391)

> "for" needs to be implemented as a special form as it emits some optimizations that are only available at the Core Erlang level.

That's interesting. I wonder if a future Elixir version could have a way of defining macros which sould emit these optimizations. Is this a likely direction for future developments?

> "with" needs to be implemented as a special form as it has different lexical properties than a bunch of nested cases.

Could you expand on this a little? What are those different lexical properties?

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Re:Elixir in Depth – Reading and personal notes by josevalim on Saturday August 19, 2017 @03:04AM (#15052105)

> That's interesting. I wonder if a future Elixir version could have a way of defining macros which sould emit these optimizations. Is this a likely direction for future developments?

To do so, we would need to compile to core, and that means tools like Cover and the Erlang debugger would no longer work with Elixir. It is unlikely we will go to this direction.

> Could you expand on this a little? What are those different lexical properties?

If you compile a "with" to a bunch of cases, a variable from the outer case would be available to both success and failure cases. Take this code:

    a = true
    with true <- a = false do
      a
    else
      _ -> a
    end

In Elixir it returns true because `a = false` has no impact on else. But if it compiled to a bunch of cases, we would get:

    a = true
    case a = false do
      true -> a
      _ -> a
    end

And that returns false.

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