This is not playing devil's advocate - this is a _VERY_ legitimate question. I'll go further and say that without a "killer app" (and/or strong corporate backer), a language doesn't typically take off nowadays, regardless how good it is ([edit] but to the point of another commenter - I do agree that "exploration" is a good enough reason; one doesn't need to write languages only with the goal of making them popular).
- Scala: only really took off with Spark (had Akka before but wasn't really that popular)
- Python: might've died if not for numpy/pandas/ ML
- Ruby: Rails
- Typescript: V8/Node.js / javascript on the server-side
- Go: Google, Kubernetes (and even so it's questionable how popular it _really_ is)
- Swift: Apple, iOS apps (to a somewhat similar extent: Kotlin, for Android development).
- C#: I can't really name the "killer app", but... Microsoft. (to be fair the "killer app" itself might be the whole MS ecosystem integration)
There are a lot of decent languages (Clojure, D) that never got popular, despite their merits. Even Kotlin mentioned above is arguably a much better choice than Java on the server side. But it's not used that much on the server, even though it actually has the answer to "what problem does it solve" (easy way to write async code in JVM, which is not a small thing)
I don't think they care so much as you think about 'takeoff'. It's mostly a research project in programming pedagogy. They're trying to make lisp features more accessible to students in universities. A takeoff would sure be appreciated, but the immediate goal is not a takeover of the industry.
The author (M Flatt) is an incredibly gifted and productive programmer, btw.
> Typescript: V8/Node.js / javascript on the server-side
I would dare to say that more people use Typescript in frontend than in backend projects, so basically Typescript killer "app" is the browser, because you are forced to use Javascript, but JS does not scale that good for mid, big projects.
I agree; but I _think_ chronologically Node & server-side-JS came first? The driver is the same though: "larger codebases, running on top of Javascript" - and indeed nowadays probably the browsers are the things that run the larger codebases.
Typescript evolved from an internal project at Microsoft where they were trying to do their own GWT, but with .NET instead of Java, the browser was definitly first.
Just like VSCode started as the Web IDE Monaco, written in this new Typescript thingie, before pivoting into Electron.
C#: ASP.NET Core (a slimmer, faster Spring Boot), EF Core (better Prism, jOOQ, etc.), very flexible build targets (JVM-style, self-contained JIT and AOT binaries), easy integration with F#, good pattern matching, access to low-level features only rivaled by Swift (although Swift has its own set of issues). Far better performance ceiling than all the languages here on the list.
You forgot async/await. But all that wasn't what propelled C# to popularity, and I say that as someone who's been writing it since 2002. It was an army of VB6 and Delphi line-of-business programmers migrating to the new stack and enterprises running Windows.
The next big killer application was Unity, which didn't even use Microsoft .NET.
Everything else is just marginal advantage: if you're a JVM shop, the existing experience of your programmers is more valuable than the speed of modern .NET or better pattern matching. But if you want to switch to making games, then switching to C# and/or C++ starts making sense.
I disagree strongly with Kotlin being a better choice than Java. Kotlin solves problems Java had 14 years ago while bringing along totally unnecessary syntax complexity. Moreover it is slow to compile and is essentially a proprietary language.
- Scala: only really took off with Spark (had Akka before but wasn't really that popular)
- Python: might've died if not for numpy/pandas/ ML
- Ruby: Rails
- Typescript: V8/Node.js / javascript on the server-side
- Go: Google, Kubernetes (and even so it's questionable how popular it _really_ is)
- Swift: Apple, iOS apps (to a somewhat similar extent: Kotlin, for Android development).
- C#: I can't really name the "killer app", but... Microsoft. (to be fair the "killer app" itself might be the whole MS ecosystem integration)
There are a lot of decent languages (Clojure, D) that never got popular, despite their merits. Even Kotlin mentioned above is arguably a much better choice than Java on the server side. But it's not used that much on the server, even though it actually has the answer to "what problem does it solve" (easy way to write async code in JVM, which is not a small thing)