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Comment by davexunit | Hacker News Reader

I've never been a fan of using "DSL" in the context of Ruby. Sure, you can do some metaprogramming, but you cannot create new syntax, change order of evaluation, etc., which I feel is a fundamental requirement for creating real EDSLs. One simple consequence of this is that you end up having to quote a lot of things.

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This surprises me. Can you offer an example of those types of problems in some Ruby code?

Let's use 'attr_reader' as a simple example. It defines a method that returns the value of a member variable. It would be nice to refer to the variable name literally, but this is not possible:

    attr_reader foo

The 'foo' above would evaluate to the contents of the variable 'foo'. So, you have to do this:

    attr_reader :foo

Because we cannot control how this code evaluated, we must quote 'foo'. This greatly limits what we can express.

That's one of the things I like about Ruby DSLs. Because the DSL is just Ruby, you can do things like:

    [:foo, :bar].each do |attribute|
        attr_reader attribute
    end

You probably wouldn't want do actually do that with attr_reader, but it is just an example.

Typically, you'd write syntactic sugar on top of regular functions, so that the underlying API is available in the host language to do things like in your example. Using Ruby's class syntax as an example, it gives you a convenient means to describe classes, but underneath that is an API for programmatic manipulation of class objects.

Ah. I see. That Ruby doesn't afford this can be somewhat annoying. A counter example is using "alias". It can accept bare words, symbols, or strings. If you really wanted to get around this you could use method_missing on the class but that can open a can of worms.

'alias' is special syntax in Ruby. This emphasizes my point: You, as the user of Ruby, do not have the power that the language designers have. You cannot create new syntax rules. I argue that this power is a necessary component for creating true EDSLs, but in practice the term is used much more loosely.

It would be nice to refer to the variable name literally

No, it would not be nice. It would be in violation with basic ruby syntax.

If that is the best example you could come up with then I'm glad ruby does not allow whatever it is that you're asking for.

>It would be in violation with basic ruby syntax.

But this isn't about regular Ruby syntax, this is about extending Ruby syntax by embedding new languages within it. A new language may have new evaluation rules. As another user points out, there's a syntax called 'alias' that works similarly to my example, so I disagree that it would be violating anything.

>I'm glad ruby does not allow whatever it is that you're asking for.

I'm essentially asking for macros commonly found in the Lisp family of languages.

there's a syntax called 'alias' that works similarly to my example

That's an unfortunate wart on the language (an inconsistency) and not related to your example at all.

I'm essentially asking for macros commonly found in the Lisp family of languages.

Can you come up with a real-world use case for that?

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