PHP Debugging Tools

Phel compiles to PHP, so every PHP debugging function is available through the php/ prefix. Reach for these alongside Phel's built-in REPL helpers.

Native var_dump()#

Any PHP function via php/ prefix:

;; Dumping a definition by its name
(def v (+ 2 2))
(php/var_dump v)
;; OUTPUT:
;; int(4)

;; Directly dumping the result of a function
(php/var_dump (+ 3 3))
;; OUTPUT:
;; int(6)

(php/die) halts execution so you can inspect at leisure.

When to use var_dump()#

• Quick debugging: no setup
• Inspect PHP objects: internal structure
• Type checks: verify type conversions
• Legacy code: existing PHP codebases

Symfony VarDumper: dump() & dd()#

Use Symfony VarDumper. Install via composer under require-dev:

"require-dev": {
    "symfony/var-dumper": "^7.4"
},

dump() a definition or result:

(php/dump (+ 4 4))
;; OUTPUT:
8

dd() dumps and halts:

(php/dd (+ 5 5))
;; OUTPUT:
10

Why Symfony VarDumper?#

Beautiful output: syntax highlighting, collapsible nested structures, better formatting than var_dump().

Rich info: object properties/methods, resource types, circular references.

Web-friendly: HTML output, dark mode, copy-to-clipboard.

Best practices#

;; Use dump() during development
(defn process-user [user]
  (php/dump user)  ; Inspect without stopping
  (-> user
      (validate)
      (save)))

;; Use dd() to stop and inspect
(defn debug-pipeline [data]
  (-> data
      (transform)
      (php/dd)  ; Stop here and inspect
      (save)))  ; Never reached

Check the evaluated PHP#

Keep generated temp PHP files for debugging. Useful when an error references /private/var/folders/.../T/__phelV2KvGD that no longer exists. See docs.

<?php # phel-config-local.php

return (require __DIR__ . '/phel-config.php')
    ->withKeepGeneratedTempFiles(true)
;

TIP: Add to .gitignore to control dev config without touching the global one.

Inspecting compiled PHP#

After withKeepGeneratedTempFiles(true):

1. Find the files in /tmp/ or system temp dir.
2. Read the PHP to see how Phel compiles.
3. Understand errors by matching line numbers.
4. Learn the compiler by seeing optimization patterns.

Example:

;; Your Phel code
(defn greet [name]
  (str "Hello, " name "!"))

Generated PHP:

<?php
// Generated PHP (simplified)
function greet($name) {
    return "Hello, " . $name . "!";
}

Useful for:

• Debugging compiler issues
• Understanding performance
• Learning Phel internals
• Reporting bugs with concrete examples

PHP error reporting#

Detailed errors in development:

<?php # phel-config-local.php

error_reporting(E_ALL);
ini_set('display_errors', '1');

return (require __DIR__ . '/phel-config.php')
    ->withKeepGeneratedTempFiles(true)
;

Catches:

• Type errors
• Undefined variables
• Deprecated calls
• Warnings and notices

Next steps#

• Phel debug helpers for native debugging
• XDebug for step-through debugging
• Config docs for more dev settings