Ashok Khanna ashok-khanna

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.

Vim: available key pairs in normal mode

All lowercase

The operators c, d, and y expect a motion, like w, e, etc. The second character in the following pairs is not a motion so it is a NOP and nothing is overridden if we use them in mappings.

cd cm co cp cq cr cs cu cx cy cz

dc dm dq dr ds du dx dy dz

Array Iteration

https://gist.github.com/ljharb/58faf1cfcb4e6808f74aae4ef7944cff

While attempting to explain JavaScript's reduce method on arrays, conceptually, I came up with the following - hopefully it's helpful; happy to tweak it if anyone has suggestions.

Intro

JavaScript Arrays have lots of built in methods on their prototype. Some of them mutate - ie, they change the underlying array in-place. Luckily, most of them do not - they instead return an entirely distinct array. Since arrays are conceptually a contiguous list of items, it helps code clarity and maintainability a lot to be able to operate on them in a "functional" way. (I'll also insist on referring to an array as a "list" - although in some languages, List is a native data type, in JS and this post, I'm referring to the concept. Everywhere I use the word "list" you can assume I'm talking about a JS Array) This means, to perform a single operation on the list as a whole ("atomically"), and to return a new list - thus making it mu

	import Darwin

	let handle = dlopen("/usr/lib/libc.dylib", RTLD_NOW)
	let sym = dlsym(handle, "random")
	let functionPointer = UnsafeMutablePointer<() -> CLong>(sym)
	let result = functionPointer.memory()

	println(result)

	// IRR swift version
	// [email protected]
	// reference http://www.codeproject.com/Tips/461049/Internal-Rate-of-Return-IRR-Calculation
	// 2016/06/23

	import UIKit


	func computeIRR(cashFlows:[Int],numOfFlows:Int) -> Double{
	//const

	From [email protected] Thu Oct 20 16:53:41 EDT 1994
	Article: 15160 of comp.lang.lisp
	Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!news.mathworks.com!usenet.eel.ufl.edu!usenet.cis.ufl.edu!caen!math.ohio-state.edu!magnus.acs.ohio-state.edu!usenet.ins.cwru.edu!ns.mcs.kent.edu!kira.cc.uakron.edu!malgudi.oar.net!malgudi.oar.net!welch
	From: [email protected] (Arun Welch)
	Newsgroups: comp.lang.lisp
	Subject: CL History (was Re: Why do people like C?)
	Date: 20 Oct 94 15:34:10
	Organization: OARnet
	Lines: 3244
	Message-ID: <[email protected]>

	let longPress = UILongPressGestureRecognizer(target: self, action: #selector(upgradeAlertViewOtherUpgradesLongPressHandler))
	longPress.minimumPressDuration = 0

	var longPressGRStartPoint: CGPoint?
	var didCancelLongPressGR = false

	func viewTouched(sender: UILongPressGestureRecognizer) {
	let currentPoint = sender.location(in: self.view)
	switch sender.state {
	case .began:

	function! BreakHere()
	s/^\(\s\)\(.\{-}\)\(\s\)\(\%#\)\(\s\)\(.\)/\1\2\r\1\4\6
	call histdel("/", -1)
	endfunction

	nnoremap <key> :<C-u>call BreakHere()<CR>

	//
	// http://raganwald.com/2019/01/14/structural-sharing-and-copy-on-write.html
	// http://raganwald.com/2019/01/26/reduce-reuse-recycle.html
	//

	const SliceHandler = {
	has (slice, property) {
	if (property in slice) {
	return true;
	}

	;; make sure you've set your default project with:
	;; gcloud config set project <project-name>

	(require 'tramp)
	(add-to-list 'tramp-methods
	'("gcssh"
	(tramp-login-program "gcloud compute ssh")
	(tramp-login-args (("%h")))
	(tramp-async-args (("-q")))
	(tramp-remote-shell "/bin/sh")