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

Found a typo? Edit this page