[G4BB3R]

The cause is not being functional, but having dozens of extra features and multiple syntaxes for the same thing, both Scala and Haskell suffer from that. On the other hand OCaml is very fast and Elm is the fastest compiler I've ever seen. Edit: oops there was already a similar comment when I posted

[saghm]

> Elm is the fastest compiler I've ever seen

Compared to the other languages you mention there, I'm not surprised that Elm has the fastest compiler; compiling to an actual binary (or something low-level like JVM bytecode) definitely seems like it would take more work to compile to than something much higher level like JavaScript, especially if you're performing optimizations at each intermediate layer. That's not to knock Elm though; obviously having a fast compile time is a good thing regardless of the reason, and it certainly still would be possible for someone to accidentally write a slow compiler to JavaScript!

[Cthulhu_]

In a modern stack though, compiling a JS or Typescript project takes ages; I don't believe it's the rewriting, optimizing and minification per se, but more the huge amounts of code and files that need to be processed.

[kaba0]

Elm is fast because it does only the subset of Haskell’s feature set. It doesn’t have as strong a type system, it uses eager evaluation and I guess it mostly falls back on the JS runtime for optimizations.

[pharmakom]

Compiling to binary can be plenty fast, especially JVM code. It’s optimisation that really takes time.

[orbifold]

In reality the Elm compiler is probably orders of magnitude slower than clang, it just has much less work to do. A C++ compiler needs to parse / preprocess 100k+ lines of code even for something like hello world.