Chidvi Doddi DoddiC

Reader Macros in Common Lisp

This post also appears on lisper.in.

Reader macros are perhaps not as famous as ordinary macros. While macros are a great way to create your own DSL, reader macros provide even greater flexibility by allowing you to create entirely new syntax on top of Lisp.

Paul Graham explains them very well in [On Lisp][] (Chapter 17, Read-Macros):

The three big moments in a Lisp expression's life are read-time, compile-time, and runtime. Functions are in control at runtime. Macros give us a chance to perform transformations on programs at compile-time. ...read-macros... do their work at read-time.

Why Python and not Haskell?

This thread asks why more Python developers couldn't instead be using Haskell: https://discourse.haskell.org/t/commercial-haskell-should-go-after-python-julia-not-rust/6964/2

One of the points made in this thread, is that there is a sizeable class of Python programmers for which the trope "Python programmers will be scared of monads!" doesn't apply. I thought I would ask some of the people I know that use Python why they don't use Haskell.

Some notes about the demographic:

These people all work as academic researchers in Computer Science, formal methods, ranging from very abstract to quite practical.
Two of them know more about Category Theory and monads than the vast majority of Haskellers.

	model: claude-opus-4-20250514
	messages:
	- role: user
	content:
	- type: text
	text: \|
	<system-reminder>
	As you answer the user's questions, you can use the following context:
	# important-instruction-reminders
	Do what has been asked; nothing more, nothing less.

	/*
	* Erdős-Selfridge Prime Categorization Engine - C11 Compatible
	* Copyright (c) 2025 H.O <opsec.ee@pm.me>
	* Target: 10+ million primes/second
	* COMPLEXITY: O(n log m) - Near-linear performance
	* Where: n = num primes, m = largest prime val
	*
	* Optimizations:
	* - Enhanced wheel factorization with branch elimination
	* - Optimized memory layout for cache performance