How to extend Crystal language syntax?

Question

For example, i want to get looks-like-native "for" loop, which was implemented in crystal's embedded macro language, but it is absent (for reasons of principle) in main, "runtime" language:

for i in list do
end

for k, v in hash do
end

(Here "{}" is a simple block. I cant use do .. end syntax here anyway (maybe not)). Will be very good to implement multi-inlcude directive, such as:

includes MixinX, MixinY, MixinZ

and so on... As i know, macro (named "for" and "includes" in the provided snippets) can't accept "i in list" without double-quoting. So... is there only one way to do so - extending crystal's syntax/lexical parser and analyzer itself?

Answer 1

Maybe, you could use something like this:

module Foo
  def foo
    "foo"
  end
end

module Bar
  def bar
    "bar"
  end
end

class Object
  macro includes(*mods)
    {% for mod in mods %}
      include  {{ mod }}
      {% end %}
  end
end

class Baz
  includes Foo, Bar
end

Baz.new.foo # => "foo"
Baz.new.bar # => "bar"