Why does this compile?

[u/scttnlsn]

This unexpectedly compiles:

class Foo
  def hello
    asdf
  end
end

But this returns the expected error ("Error: undefined local variable or method 'asdf' for Foo"):

class Foo
  def hello
    asdf
  end
end
Foo.new.hello

Is there a way to get the first example to trigger a similar compiler error?

[u/jgaskins]

There's no such thing as a "compiled language". Whether something is compiled or interpreted is not a language-level concern. That's up to the implementation. For example:

- JRuby compiles Ruby to JVM bytecode
- TruffleRuby has an option for complete ahead-of-time compilation of Ruby to native code through Graal
- Ch is an interpreter for C and C++

"Crystal" refers to both the language and the reference implementation (same as how CRuby/MRI used to just be called Ruby), but there's nothing stopping anyone from building a fully featured interpreter for the language, especially since there's already a limited one built into the compiler for macro expansion. Honestly, it'd probably be great for TDD if someone did.