There are essentially two ways we learn to trust stuff. Either (a) we have it (formally) proved (no one reasonable doubts 1 + 1 = 2) or (b) we rely on tons of everyday experience to note that it doesn't fail (we mostly trust our cars).
Scala has neither. I would not be surprised if the compiler contained serious bugs.
Many programmers only have experience of web applications or services, and complain that some dinosaurs insist on 20-year-old languages.
My point is that there are fields in which this convservatism is the correct attitude, and that programmers who point the finger and laugh at such out-dated thinking lack experience.
I work in a field that requires fewer bugs than most (although it's not as severe as ATC), and we don't have much choice about the languages we use.
That would not be so much of a problem. Scheme is certainly older than 20 years, now. Python comes close.
The R3RS that existed in 1989 lacked macros, had t and nil, and even allowed implementations to "call" strings. Even ten years ago, Python, as it existed in 1999 was a very different language than it is today.
Moreover, Python and scheme implementations have code that "worked" only a few years ago that fails to run on the current version of the interpreters, while gcc still happily recompiles my pre-ansi C just fine.
>> that some dinosaurs insist on 20-year-old languages
> That would not be so much of a problem. Scheme is
> certainly older than 20 years, now. Python comes close.
The point isn't about age, it's about the popularity and maturity of the language, and through them, the acceptability.
But I'm pretty sure you knew that, so maybe I'm missing something deeper in your comment.
As you say, it is about the `mainstreamness' of the language.
Insert:
>> That would not be so much of a problem. [But there are other problems.]