Clojure REPL Evaluation

Evaluate Clojure code via nREPL using clj-nrepl-eval.

Discovering nREPL Servers

Before evaluating, discover available nREPL ports:

clj-nrepl-eval --discover-ports

This scans .nrepl-port files and running JVM/Babashka processes in the current directory.

To see previously connected servers:

clj-nrepl-eval --connected-ports

Starting a REPL in XTDB

Start the Gradle REPL:

./gradlew :clojureRepl

For a specific port:

./gradlew :clojureRepl -PreplPort=7888

Evaluating Code

Simple Expressions

clj-nrepl-eval -p 7888 "(+ 1 2 3)"

Multiline Code (Heredoc)

Use heredoc for complex code to avoid escaping issues:

clj-nrepl-eval -p 7888 <<'EOF'
(require '[xtdb.api :as xt])
(xt/status dev/node)
EOF

Piping Code

echo "(+ 1 2 3)" | clj-nrepl-eval -p 7888

Session Persistence

Sessions persist by default. Each host:port has its own session file. State (vars, namespaces, loaded libraries) persists across invocations until the nREPL server restarts.

# First call - define a var
clj-nrepl-eval -p 7888 "(def x 10)"

# Later call - x is still available
clj-nrepl-eval -p 7888 "(+ x 20)"

Reset Session

If session becomes corrupted:

clj-nrepl-eval -p 7888 --reset-session

Or reset and evaluate:

clj-nrepl-eval -p 7888 --reset-session "(def x 1)"

Common XTDB Workflows

Reload and Test a Namespace

clj-nrepl-eval -p 7888 "(require 'xtdb.vector.reader :reload)"

Run Tests

clj-nrepl-eval -p 7888 <<'EOF'
(require 'xtdb.vector.reader-test :reload)
(clojure.test/run-tests 'xtdb.vector.reader-test)
EOF

Check dev Node Status

clj-nrepl-eval -p 7888 <<'EOF'
(require 'dev)
(in-ns 'dev)
(xt/status node)
EOF

Options

• -p, --port PORT - nREPL port (required)
• -H, --host HOST - nREPL host (default: 127.0.0.1)
• -t, --timeout MILLISECONDS - Timeout (default: 120000)
• -r, --reset-session - Reset persistent nREPL session
• -c, --connected-ports - List active connections
• -d, --discover-ports - Discover nREPL servers
• -h, --help - Show help

When to Use

Use this skill to:

• Verify code changes compile correctly
• Test functions interactively
• Run tests after modifications
• Check REPL state during development

Do NOT use for:

• File operations (use Read, Edit, Write, Glob, Grep instead)