ericdallo/dotfiles/ericdallo-brepl

brepl - Evaluating Clojure Code

CRITICAL: Load This Skill First

You MUST load this skill before using brepl. Do NOT attempt to use brepl without loading this skill first, or you will use incorrect syntax.

Overview

brepl is a REPL client for evaluating Clojure expressions. This skill teaches the heredoc pattern for reliable code evaluation.

Always load this skill before using brepl. Always use the heredoc pattern for all Clojure code evaluation.

The Heredoc Pattern - Default Approach

Always use heredoc for brepl evaluation. This eliminates quoting issues, works for all cases, and provides a consistent, reliable pattern.

Syntax (Stdin - Recommended)

brepl <<'EOF'
(your clojure code here)
EOF

This is the simplest heredoc syntax - stdin feeds directly to brepl.

Alternative Syntax (Positional Argument)

For simple one-liners, you can use positional arguments:

brepl '(+ 1 2 3)'

Heredoc is preferred for anything with quotes or multiple lines.

Note: The -e flag is optional - brepl automatically treats stdin and positional arguments as code to evaluate.

Important: Use <<'EOF' (with quotes) not <<EOF to prevent shell variable expansion.

Examples

Multi-line expressions:

brepl <<'EOF'
(require '[clojure.string :as str])
(str/join ", " ["a" "b" "c"])
EOF

Specific nREPL port

brepl -p 1234 '(+ 1 2 3)'

Code with quotes:

brepl <<'EOF'
(println "String with 'single' and \"double\" quotes")
EOF

Reloading and testing:

brepl <<'EOF'
(require '[myapp.core] :reload)
(myapp.core/some-function "test" 123)
EOF

Complex data structures:

brepl <<'EOF'
(def config
  {:database {:host "localhost"
              :port 5432
              :name "mydb"}
   :api {:key "secret-key"
         :endpoint "https://api.example.com"}})
(println (:database config))
EOF

Running tests:

brepl <<'EOF'
(require '[clojure.test :refer [run-tests]])
(require '[myapp.core-test] :reload)
(run-tests 'myapp.core-test)
EOF

Alternative: Simple Expressions

For very simple expressions, you can use direct positional arguments:

# Simple expression
brepl '(inc 1)'
 
# Same with heredoc (consistent approach)
brepl <<'EOF'
(inc 1)
EOF

Why prefer heredoc: No mental overhead deciding which pattern to use, no risk of quoting issues, easy to extend.

Loading Files

To load an entire file into the REPL:

brepl -f src/myapp/core.clj

After loading, you can evaluate functions from that namespace using either pattern.

Fixing Unbalanced Brackets

Use brepl balance to fix unbalanced brackets in Clojure files using parmezan:

# Fix file in place (default)
brepl balance src/myapp/core.clj
 
# Preview fix to stdout
brepl balance src/myapp/core.clj --dry-run

This is useful for recovering files with bracket errors.

Common Patterns

Namespace reloading

brepl <<'EOF'
(require '[myapp.core] :reload-all)
EOF

Documentation lookup

brepl <<'EOF'
(require '[clojure.repl :refer [doc source]])
(doc map)
(source filter)
EOF

Error inspection

brepl <<'EOF'
*e
(require '[clojure.repl :refer [pst]])
(pst)
EOF

Critical Rules

1. Always use heredoc - Use the heredoc pattern for all brepl evaluations
2. Quote the delimiter - Always use <<'EOF' not <<EOF to prevent shell expansion
3. No escaping needed - Inside heredoc, write Clojure code naturally
4. Multi-step operations - Combine multiple forms in one heredoc block
5. Write correct Clojure - Ensure proper bracket balancing and valid syntax

Why Always Use Heredoc

Consistency over optimization. While simple positional arguments work for basic cases, using heredoc everywhere means:

1. No decision fatigue - One pattern for everything
2. No quoting errors - Everything between <<'EOF' and EOF is literal
3. Easy to extend - Add more lines without changing syntax
4. Readable - Clear where the code starts and ends
5. Safe - No shell interpretation of Clojure code

Shell quoting with Clojure is error-prone: Clojure uses both single and double quotes, nested quotes require escaping, and reader macros can confuse the shell. Heredoc eliminates all these issues.

Resources

brepl documentation: https://github.com/licht1stein/brepl