nrepl-example

nrepl-example

A jolt app that starts an nREPL server and keeps running, so you can connect from your editor and drive the live process. The motivating use case is a binary deployed somewhere headless — say a Raspberry Pi reading sensors — that runs its loop unattended while you reach in over nREPL to inspect state, flip outputs, reload code, or call functions without an SSH-and-restart cycle.

(require '[app.core :as app])
(app/status)        ; => {:ticks 19 :led true :sensor 46.24...}
(app/toggle-led!)   ; => true
(app/log! "hi")     ; => 2
(app/recent-log)    ; => ["system started" "hi"]

The "device" is simulated (a counter and a sine-wave sensor reading), but the plumbing is real: a background loop mutates an atom, and the nREPL middleware (eval, sessions, completion, lookup) comes from the jolt-lang/nrepl library.

Run in dev

Interpreted, with the nREPL server on 127.0.0.1:7888:

jolt run -m app.core

It writes .nrepl-port and parks until ^C. Point CIDER / Calva / Cursive at that port and you're in a live REPL over the running process.

Run the test suite (starts the server in-process, connects a client, drives state over the wire, checks the device loop):

jolt -M:test

For an ad-hoc REPL into this project without running the app's main:

jolt nrepl

Compile for release

A self-contained native binary (no jolt, no JVM, ~MBs):

jolt build -m app.core -o nrepl-example
./nrepl-example          # listens on 7888
./nrepl-example 4005     # or pass a port

The port also comes from the first arg, else $JOLT_NREPL_PORT, else 7888. The binary writes .nrepl-port on start and removes it on ^C (shutdown hooks close the server and stop the device loop). Connect an editor exactly as in dev — the binary is as driveable as the interpreted run.

macOS builds are unsigned. To run one on another Mac, clear the quarantine bit first: xattr -d com.apple.quarantine ./nrepl-example.

How it works

• start-nrepl! mirrors what jolt nrepl does: it blocks SIGINT on the main thread (so ^C lands there, not on the server's socket recv), starts the server on a worker thread with the library middleware, and registers its stop fn as a shutdown hook.
• start-device-loop! runs the simulated device on a future; park-until-interrupt in -main is what keeps the process alive — returning from -main would let the launcher exit.
• Device state lives in a defonce atom (app.core/system), so reloading the namespace from a connected editor doesn't wipe what the loop has accumulated.

Requirements

• jolt on PATH.
• The jolt-lang/nrepl dependency is fetched automatically from git on first run.