I was telling a Java programmer about Elm recently. A Java programmer who works on low-level Java code for HPC, He didn’t like that Elm was immutable giving the example of quick sort. Quick sort is only quick sort if you are actually using mutable arrays - you can write the algorithm on top of the immutable HAMT arrays we have in Elm, but its not really the same algorithm. I did explain to him that the performance of Elm is very good, good enough for its domain generally.
But its a fair point. Web servers written in Java can be extremely efficient with low-latency and high throughput and handling thousands of connections - in part because of mutable arrays. This feels like something that Elm on the back-end could never compete with.
I imagine that a back end Elm would focus more on higher level things, like writing business logic or web APIs. When I think of all the service logic I’ve written or seen in Java, I now think of how much better that would be in Elm.