Why Phel?

You know PHP. Why learn a Lisp on the same runtime?

Honest answers below. If Phel doesn't fit, that's fine.

Do I need to know Lisp?#

No. One rule: the first element inside parentheses is the function, the rest are arguments — (map fn arr), (php/str_contains haystack needle). No operator precedence, no special cases. Phel in 5 Minutes walks through the syntax; practice exercises get you comfortable in an hour.

Why Lisp syntax specifically?#

1. Homoiconicity. Code is data (lists, vectors, maps). Macros manipulate code with the same functions you use on data.
2. Macros. Extend the language with built-in-looking syntax. See Macros.
3. Regularity. One pattern: (function arg1 arg2 ...). Read any Phel code once you internalize it.

Unfamiliar feeling fades within days of use.

Why not just modern PHP?#

Modern PHP is great. Some things aren't on its roadmap:

• Immutable data structures by default. Eliminates stale state, unexpected mutations, order-dependent side effects.
• Real macro system. Operates on code as data. PHP attributes and codegen are not the same.
• REPL-driven development. Evaluate expressions interactively, build incrementally. See REPL.
• Functional-first design. Pure functions, pipelines, data transformation. PHP allows FP but pushes OOP.

Phel and PHP optimize for different things on the same runtime.

Can I use existing PHP libraries?#

Yes. Any Composer package, class, trait, function, or constant is callable through the php/ prefix — e.g. (php/strlen "hello") or (php/-> (php/new DateTimeImmutable "2024-01-15") (format "Y-m-d")). The full escape hatch (methods, statics, constants, php/aget) is in PHP Interop.

Isn't a compilation step a hassle?#

No. vendor/bin/phel run or the REPL compiles transparently. No build pipeline, watcher, or output dir. Same idea as TypeScript or Sass. Deploys as plain PHP.

What about performance?#

Phel compiles to plain PHP, so the bulk of your code runs at PHP speed. The real overhead is the persistent (immutable) data structures: an "update" allocates a new structure with structural sharing (O(log32 n)) rather than mutating in place, so they are slower than a native PHP array write. For most web, CLI, and data-processing work that cost is negligible.

In a hot inner loop over millions of elements, reach for native PHP arrays through PHP interop (php/aset, php/aget, php/apush) and stay on the fast path, then hand the result back as a Phel value. Everywhere else, immutability buys correctness and clearer code for a price you will not notice.

What about debugging?#

Full PHP debugging ecosystem works:

• Phel helpers: tap>, add-tap, pprint.
• PHP native: var_dump, print_r, Symfony dump(). Phel values are PHP objects.
• XDebug: step-through, breakpoints, variable inspection. PhpStorm and VS Code.

See Debug helpers and XDebug setup.

What about IDE support?#

VS Code, PhpStorm, Emacs, Vim: syntax highlighting, REPL/nREPL, formatting. See Editor Support.

Is Phel production-ready?#

Core is stable and tested. Good fit for:

• Side projects, personal tools
• CLI applications
• Internal tools and scripts
• Learning FP on a runtime you know
• REPL-driven prototyping

Community small but active. Need LTS-grade enterprise stability? Not yet. Want expressive PHP and OK being an early adopter? Phel delivers.

See awesome-phel for libraries, tools, and projects.

Next steps#

• Getting Started: zero to a live REPL.
• PHP Interop: call any PHP function or class.
• Cheat Sheet: core syntax and functions in one page.