Ruby and Scala are for two different kinds of environments. One is an environment where having less code to maintain (that can also be highly legible) matters and where you have a lot of options. The other is an environment where an edge in performance is more important, but not important enough to write it in an even faster language/not run in the JVM at all.<p>I noticed a lack of a link to a 1:1 comparison of application code with realistic examples. I think such comparisons and related discussion are often the best way to convince someone to use a language.<p>And some slides were just blatantly wrong, like Mixin Abuse: apparently that is just a long list of module includes? I have never seen so many module includes in a single class in application code. But, assuming you did have that, you should show what it would look like side-by-side in Scala. In Ruby, there are a lot of options when it comes to including other code or defining code in a class, instance, etc. Those options can lead to much less and more legible code if used correctly.<p>I remember when people said Java was slow; they made it seem like it was a fad, and no reputable company would use it. And... we see where that went.