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Hofstadter on Lisp

In the mid-80s, while reading through my roommate's collection of Scientific American back issues, I encountered this introduction to Lisp written by Douglas Hofstadter. I found it very charming at the time, and provide it here (somewhat illegally) for the edification of a new generation of Lispers.

In a testament to the timelessness of Lisp, you can still run all the examples below in emacs if you install these aliases:

(defalias 'plus #'+)
(defalias 'quotient #'/)
(defalias 'times #'*)
(defalias 'difference #'-)

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Configuring Meraki Client VPN in Linux

You can try the official Meraki Configuring Client VPN in Linux article for GUI based setup. For terminal based configuration, see below.

Install packages

Install the following packages:

• strongswan
• xl2tpd

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# adapted from http://spottedhyena.co.uk/centos-67-ipsecl2tp-vpn-client-unifi-usg-l2tp-server/
yum -y install epel # different on amazon linux
sudo yum -y install xl2tpd openswan
systemctl start ipsec.service
service ipsec start

# 'myserver.com' is just to help identify. these are all imported into /etc/ipsec.conf.

vim /etc/ipsec.d/myserver.com.conf # see next...

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(ns cognician.db.translate
  (:require [datomic.api :as d])
  (:import [clojure.lang MapEntry]
           [datomic.query EntityMap]))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Language

(def default-language :en-GB)

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Latency Comparison Numbers
--------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

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(def payment-codes-per-block 4096)

(defn create-payment-code-feed
  [db]
  (let [payment-code-feed (chan 10)]
    (go-loop []
             (let [block-id (allocate-block db)
                   block-start (* block-id payment-codes-per-block)]
               (-> (onto-chan payment-code-feed
                              (->>

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(ns bs.utils.mock-connection
  "Utilities for using Datomic"
  (:require [datomic.api :as d])
  (:use clojure.repl clojure.pprint)
  (:import (java.util.concurrent BlockingQueue LinkedBlockingDeque)
           (datomic Connection)))

(defrecord MockConnection
  [dbAtom, ^BlockingQueue txQueue]

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;; Adds support to Transit for emitting Joda DateTimes in the same format as standard java.util.Date.

;; Dependencies: [clj-time "0.9.0"] and [com.cognitect/transit-clj "0.8.259"] (newer version will likely still work)

(require '[cognitect.transit :as transit])
(require '[clj-time.coerce :as coerce])
(import '[java.io ByteArrayOutputStream])

(def ^:private joda-time-verbose-handler
  (transit/write-handler

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(use '[datomic.api :only [db q] :as d])

(def schema
  [{:db/doc "A persons name"
    :db/id #db/id[:db.part/db]
    :db/ident :name
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/one
    :db.install/_attribute :db.part/db}
   

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(ns favila.datomic-util.restore-datoms
  "A \"manual\" datomic database restore.
  
  Writes raw datoms (stored in a stream written by d/datoms) to an empty database.
  Useful for memory databases: you can write out all the datoms in it, then read
  them into another database. (Note mem dbs have no log or retractions)."
  (:require [datomic.api :as d]
            [clojure.edn :as edn]))

(defrecord datom [e a v tx added?])