Why Common Lisp Is Now the Best Programming Language

gist

Vivien Henz argues Common Lisp is now the best language because large language models (LLMs) make fast feedback and short code matter most. Common Lisp runs as a live image in memory, so redefined functions take effect without a restart, and errors open a debugger an LLM can use to fix and resume the program. Macros let developers build a domain language that Henz says users could safely extend with an LLM. Henz reports Common Lisp apps about six to seven times shorter than Python versions and accepts its small library ecosystem and 1994 standard.

ideas

• LLMs moved the bottleneck from writing code to checking it. Henz says rebuilding before each check can take a few minutes, so the length of the feedback loop now decides how fast you can build.
• Common Lisp's live image removes the rebuild step. A new version of a function replaces the old one in memory, and an error opens a debugger with the whole stack instead of crashing, so an LLM can fix it and resume.
• Macros let a program grow its own domain language. Henz argues that an ERP (enterprise resource planning system) written in its own domain language would let users ask an LLM for changes that fit the product instead of breaking it.
• Shorter programs cost fewer tokens and fit in the context window. Henz says many LLM bugs come from changing one piece of a program without seeing the rest, which happens less when the whole program fits.
• Henz treats the small ecosystem and frozen standard as acceptable. Quicklisp, the main package manager, has a couple thousand projects against npm's millions, but LLMs can write or port what is missing, and the ANSI standard has not changed since 1994.

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