I wouldn't say that it's about performance for Elm. Its virtual-dom has been shown to be wickedly fast with pure code. It's more that real programs need real e

I wouldn't say that it's about performance for Elm. Its virtual-dom has been shown to be wickedly fast with pure code. It's more that real programs need real effects: you need to send HTTP requests, read from user input, etc. Elm gives you a managed way to deal with those effects, while keeping the program declarative, and making as much of the logic side-effect free as is possible.