Fast edit/run feedback loop for Scala using Nailgun

Nailgun.sh

# Step 1: install coursier and nailgun
brew install nailgun coursier/formulas/coursier

# Step 2: start nailgun server with the Scala compiler on the classpath
cs launch com.martiansoftware:nailgun-server:0.9.1 org.scala-lang:scala-compiler:2.13.1 --main com.martiansoftware.nailgun.NGServer -- 2113 &

# Step 3: create basic Scala hello world
echo 'println("Hello world!")' > Main.scala

# Step 4: assemble the classpath.
# You need at least the standard library, but you can add more libraries (for example JSON).
CLASSPATH=$(cs fetch --classpath org.scala-lang:scala-library:2.13.1)

# Step 5: evaluate the Scala hello world program with the nailgun server
for i in {1..1000}; do
  time ng --nailgun-port 2113 scala.tools.nsc.MainGenericRunner -classpath $CLASSPATH -usejavacp Main.scala
done
 
# Once the nailgun process becomes hot, the compile+run feedback loop eventually becomes around ~200ms
# > Hello world!
# > real	0m0.199s