1. Clojure: The Modern, Practical Lisp
Clojure is the most obvious next stop for any Lisp enthusiast. It’s a modern Lisp dialect that runs on the Java Virtual Machine (JVM) and JavaScript runtimes, giving you access to enormous, mature ecosystems. Creator Rich Hickey designed it with a pragmatic
focus, particularly on concurrency. Where Common Lisp is famously dynamic and mutable, Clojure doubles down on functional programming by making its data structures immutable by default. This, combined with its Software Transactional Memory (STM) system, makes writing clean, multi-threaded code much simpler. For a Common Lisp programmer, Clojure feels familiar yet new. You still get the power of a code-as-data philosophy and a robust macro system, but with a strong emphasis on functional purity and seamless Java interoperability.
2. Racket: The Language for Building Languages
If the part of Common Lisp you love most is its ability to create domain-specific languages (DSLs), then Racket is your playground. A descendant of Scheme, Racket is designed from the ground up to be a language for creating other languages. While Common Lisp's macro system is supremely powerful, Racket provides a more structured, arguably safer framework for this kind of metaprogramming, including hygienic macros that prevent accidental variable conflicts. It comes with extensive documentation and libraries, making it feel more "batteries-included" out of the box than many Common Lisp setups. For Lispers who appreciate interactivity, some find Racket's REPL experience less dynamic than a live Common Lisp image with SLIME, but its strengths in language-oriented programming are second to none.
3. Julia: The High-Performance Contender
At first glance, Julia seems like a language for scientists and data analysts, a competitor to Python and R. But under the hood, it has a Lisp-shaped soul. Julia's strongest legacy from Lisp is its powerful metaprogramming. Like Lisp, Julia's code is represented as a data structure that the language itself can manipulate, allowing for true Lisp-style macros that operate on the abstract syntax tree (AST). This is a world away from the simple text substitution of C-style preprocessors. For a Common Lisp programmer, Julia's multiple dispatch system will also feel reminiscent of the Common Lisp Object System (CLOS). It offers a compelling blend of interactive, dynamic development with performance that rivals C or Fortran, a combination Lisp programmers have always chased.
4. Elixir: The Concurrency and Metaprogramming Specialist
If you're intrigued by massive concurrency and fault tolerance, Elixir is worth a serious look. Running on the battle-tested Erlang VM (BEAM), Elixir was built for creating scalable, distributed systems. But why would a Lisp fan love it? The answer is macros. Elixir boasts a powerful macro system heavily inspired by Lisp, allowing you to mold the language and create expressive DSLs. While its Ruby-inspired syntax isn't homoiconic on the surface, the code is represented underneath in a way that's accessible to macros, just like Lisp's s-expressions. This gives developers a similar feeling of being able to program the programming language itself. For a Lisper, learning Elixir is a chance to see Lisp's metaprogramming ideas applied to the unique problem domain of concurrency and reliability.
5. Smalltalk: The Philosophical Sibling
This is the deep cut. Smalltalk and Lisp are two of the most influential languages in history, and they share a profound philosophical connection. While Lisp is built on the idea that "code is data," Smalltalk is built on the inverse: "data is code" (in the form of live objects). The result is the same: an incredibly dynamic, interactive environment where the line between the programming language and the running application blur. Common Lisp programmers cherish the experience of live coding and modifying a running system via SLIME. Smalltalk takes this even further with its "image-based" environment, where the entire system—IDE, compiler, and your application—is a collection of live, inspectable objects. It’s a different path to the same destination of ultimate malleability that Lispers have always prized.
