Running a REPL

Babashka supports running a REPL, a socket REPL and an nREPL server.

REPL

To start the REPL, type:

$ bb --repl

To get history with up and down arrows, use rlwrap:

$ rlwrap bb --repl

Socket REPL

To start the socket REPL you can do this:

$ bb --socket-repl 1666
Babashka socket REPL started at localhost:1666

Now you can connect with your favorite socket REPL client:

$ rlwrap nc 127.0.0.1 1666
Babashka v0.0.14 REPL.
Use :repl/quit or :repl/exit to quit the REPL.
Clojure rocks, Bash reaches.

bb=> (+ 1 2 3)
6
bb=> :repl/quit
$

The --socket-repl option takes options similar to the clojure.server.repl Java property option in Clojure:

$ bb --socket-repl '{:address "0.0.0.0" :accept clojure.core.server/repl :port 1666}'

Editor plugins and tools known to work with a babashka socket REPL:

Emacs: inf-clojure:

To connect:

M-x inf-clojure-connect <RET> localhost <RET> 1666

Before evaluating from a Clojure buffer:

M-x inf-clojure-minor-mode
Atom: Chlorine
Vim: vim-iced
IntelliJ IDEA: Cursive

Note: you will have to use a workaround via tubular. For more info, look here.

pREPL

Launching a prepl can be done as follows:

$ bb --socket-repl '{:address "0.0.0.0" :accept clojure.core.server/io-prepl :port 1666}'

or programmatically:

$ bb -e '(clojure.core.server/io-prepl)'
(+ 1 2 3)
{:tag :ret, :val "6", :ns "user", :ms 0, :form "(+ 1 2 3)"}

nREPL

To start an nREPL server:

$ bb --nrepl-server 1667

Then connect with your favorite nREPL client:

$ lein repl :connect 1667
Connecting to nREPL at 127.0.0.1:1667
user=> (+ 1 2 3)
6
user=>

Editor plugins and tools known to work with the babashka nREPL server:

Emacs: CIDER
lein repl :connect
VSCode: Calva
Atom: Chlorine
(Neo)Vim: vim-iced, conjure, fireplace

The babashka nREPL server does not write an .nrepl-port file at startup, but you can easily write a script that launches the server and writes the file:

#!/usr/bin/env bb

(import [java.net ServerSocket]
        [java.io File]
        [java.lang ProcessBuilder$Redirect])

(require '[babashka.wait :as wait])

(let [nrepl-port (with-open [sock (ServerSocket. 0)] (.getLocalPort sock))
      cp (str/join File/pathSeparatorChar ["src" "test"])
      pb (doto (ProcessBuilder. (into ["bb" "--nrepl-server" (str nrepl-port)
                                       "--classpath" cp]
                                      *command-line-args*))
           (.redirectOutput ProcessBuilder$Redirect/INHERIT))
      proc (.start pb)]
  (wait/wait-for-port "localhost" nrepl-port)
  (spit ".nrepl-port" nrepl-port)
  (.deleteOnExit (File. ".nrepl-port"))
  (.waitFor proc))

Debugging the nREPL server

To debug the nREPL server from the binary you can run:

$ BABASHKA_DEV=true bb --nrepl-server 1667

This will print all the incoming messages.

To debug the nREPL server from source:

$ git clone https://github.com/borkdude/babashka --recursive
$ cd babashka
$ BABASHKA_DEV=true clojure -A:main --nrepl-server 1667

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