---
name: babashka-nrepl
description: Write Clojure (Babashka) scripts using REPL-driven development. Start an nREPL server and send code to it for evaluation as you develop.
---

# Preparation

To proceed with REPL-driven development, you first need to start an nREPL server.

## Optional: Create bb.edn

If additional libraries are needed, create `bb.edn` in the working directory before starting the nREPL server.

```clojure
{:deps
 { ;; Declare required dependencies here
 }}
```

If you add libraries, you need to restart the nREPL server each time.

## Start nREPL Server

The nREPL server can be started with the following command:

    bb nrepl-server ${port}

The port is arbitrary, but `1667` is used by default.
Since you will send code from another process using an nREPL client, it's recommended to start this process asynchronously.
Terminate the entire process when you're done.

# Usage

## nREPL Client

You can send Clojure (Babashka) code to the nREPL server with the following command:

    bb nrepl-eval ${port} '${code}'

However, this command requires a pre-defined `bb.edn`, so execute it in the directory where this skill exists.

## REPL-driven development (RDD)

As you write functions, send them to the REPL one by one to verify their behavior.
It's recommended to verify behavior in the smallest possible units.

On RDD, it is encouraged to run and verify as many functions and code snippets as possible.
Don't be lazy to eval your code.

### Example

    $ bb nrepl-eval 1667 '(defn double [x] (* x 1)'
    clojure.lang.ExceptionInfo: EOF while reading, expected ) to match ( at [1,1] user REPL:1:25

Fix the number of parentheses.

    $ bb nrepl-eval 1667 '(defn double [x] (* x 1))'
    #'user/double

Then, execute the defined function `double`.

    $ bb nrepl-eval 1667 '(double 3)'
    3

It is not expected behavior. Fix it.

    $ bb nrepl-eval 1667 '(defn double [x] (* x 2))'
    #'user/double

Verify the behavior again.

    $ bb nrepl-eval 1667 '(double 3)'
    6