For faster edit-compile-run cycle it is recommended to to use GHCJSi as follows.

First, enter the Nix configured shell environment:

nix-shell -A env

Then, enter the GHCJSi shell:

cabal configure --ghcjs
cabal repl

GHCJSi starts up a web server. You should immediately connect to it from the web browser via http://localhost:6400/

From the GHCJSi shell--and everytime Main.js changes--recompile and send the new code to the browser:

> import Miso.Dev  # Once
> :r
> clearBody >> main

The UI in the web browser will now update automatically with the new code. Happy hacking!

This application can be built for production and run as follows:

nix-build
warp -d result/bin/app.jsexe/  # Port 3000