PHP Debugging Tools

Since Phel compiles to PHP, you can use familiar PHP debugging functions and tools. These are perfect for quick inspections and work alongside Phel's built-in helpers.

Native var_dump()#

You can use any PHP function simply using the 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)

Additionally, you can call (php/die) to force the execution of the process so that you can debug a particular value at your own rhythm.

When to use var_dump()#

  • Quick and dirty debugging: No setup required
  • Inspecting PHP objects: See internal PHP structure
  • Checking types: Verify PHP type conversions
  • Legacy code: When working with existing PHP codebases

Symfony VarDumper: dump() & dd()#

Symfony has an awesome VarDumper Component which you can use in your Phel projects as well. You can install it by using composer, under your require-dev dependencies.

"require-dev": {
    "symfony/var-dumper": "^5.4"
},

And then, the same drill, you can dump() a definition by its name or the function result:

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

Additionally, you can also use dd() to dump and die the execution of the program as soon as it reaches that point:

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

Why Symfony VarDumper?#

Beautiful output:

  • Syntax highlighting
  • Collapsible nested structures
  • Better formatting than var_dump()

Rich information:

  • Object properties and methods
  • Resource types
  • Circular references detection

Web-friendly:

  • Nice HTML output in browsers
  • Dark mode support
  • Copy-to-clipboard functionality

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#

You can keep the generated temporal PHP files for debugging purposes. Useful when you see an error occurring on /private/var/folders/qq/dvftwj.../T/__phelV2KvGD but the file does not exist. Read the docs.

<?php # phel-config-local.php

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

TIP: Add this file to the .gitignore of the project, so you can have control over the configuration while on development without changing the global config.

Inspecting Compiled PHP#

Once you enable setKeepGeneratedTempFiles(true), you can:

  1. Find the generated files: Look for temp files in /tmp/ or your system's temp directory
  2. Read the PHP code: See exactly how Phel compiles to PHP
  3. Understand errors: Match error line numbers to your Phel code
  4. Learn the compiler: See optimization patterns

Example workflow:

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

With setKeepGeneratedTempFiles(true), you can find and read the generated PHP:

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

This is invaluable for:

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

PHP Error Reporting#

Enable detailed error reporting during development:

<?php # phel-config-local.php

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

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

This helps catch:

  • Type errors
  • Undefined variables
  • Deprecated function calls
  • PHP warnings and notices

Next Steps#

← Previous XDebug Setup
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