Ahmed Hassan ahmed1hsn

xitdb-clj is a new immutable database for Clojure. It can time travel like Datomic, and store data in a single file like SQLite. On its own, though, it has no query language. Enter Datascript...

Datascript is normally an in-memory database, but it lets you use anything as backing storage. What if we combined them?

Datascript's storage feature doesn't tell us exactly what changed, so I added one more trick: Editscript, the diffing library. I use it to figure out how to update the database with the minimal number of changes.

The end result is a sort of mini Datomic that writes to a single file. And yet, this setup can do something Datomic can't: it can branch off of any old copy of the database. The example below reverts to an older copy of the database.

Keep in mind that all reads and writes are incremental. The database is not being loaded into memory at once, so you can use it to

When to use `assert`?

In JVM Clojure, Exceptions are for operating errors ("something went wrong") and Assertions are for programmer and correctness errors ("this program is wrong").

An assert might be the right tool if throwing an Exception isn't enough. Use them when the assertion failing means

there's a bug in this program (not a caller)
what happens next is undefined

This is a simple demo of how latest Bun could've implemented .as(Class) instead of using the quite jurassic Object.create which is slow, bloated due descriptors logic, if used at all, and incapable to play nicely with features introduced after Object.create was even specified.

// what `as(Class)` should return
const { assign } = Object;
const asClass = new WeakMap;
const setAsClass = Class => {
  class As extends Class {
    constructor(fields) {
      assign(super(), fields);

FlowStorm Quickstart

FlowStorm is a time-travelling debugger for clojure.

IMO, Clojure has the best development experience with its REPL-driven workflow. FlowStorm makes it even better.

Most notably:

"time-traveling" retrospective debugger (walk forward and backward, search for values)
zero-config tap> destination
retroactively add print statements to previous evaluations

References — Electric Clojure

Electric Clojure implements a form of arrowized continuous time dataflow programming with extensions for network-transparent function composition.

The Haskell School of Music: From Signals to Symphonies (2018) — best starting point and also a great intro to Haskell.
The Essence of Dataflow Programming (2006) great category theory overview of dataflow programming; missing Applicative (2008), Free monad and Cofree comonad
Push-pull functional reactive programming, Elliot (2009)
Breaking down FRP, Jane Street (2014) — good concise comparision of many FRP aspects; missing discussion of discrete vs continuous
[Compiling to Categories, Elliott (2017)](http

Missionary concept map

Missionary primitives fit into three categories:

Effect descriptions = pure functional programming which is about trees not graphs

continuous flow, m/?< (switch)
m/watch, m/latest, m/cp
m/observe
m/reductions, m/relieve

	(defcustom microjournal-path "~/.journal.org.gpg"
	"name for the microjournal file"
	:type 'file
	:group 'microjournal)

	(defun microjournal-insert-year ()
	"Create a root header for the current year if it doesn't exist"
	(interactive)
	(let ((header-name (format-time-string "%Y")))
	(goto-char (point-max))

	(ns flexi-clock
	(:import (java.time Clock Duration Instant ZonedDateTime)))

	(defn clock
	"potential library function (e.g. in tick or tempo).

	This just implements the platform Clock - which works because non-test code only uses that API.
	Any manipulation of time (which happens in testing code) is done via changing
	what get-instant and get-zone return"
	[get-instant get-zone]

	(ns jst
	(:require [camel-snake-kebab.core :as csk]
	[clojure.string :as string]
	[hyperfiddle.rcf :refer [tests]]))

	(hyperfiddle.rcf/enable!)
	;; Implements a hiccup compiler into js-template.
	;;
	;; Usage: (jst cljs-symbol? template-fn? hiccup), where:
	;; cljs-symbol - what symbol implements js-template in cljs (default: shadow.cljs.modern/js-template)

	;
	; Copyright © 2023 Peter Monks
	;
	; This Source Code Form is subject to the terms of the Mozilla Public
	; License, v. 2.0. If a copy of the MPL was not distributed with this
	; file, You can obtain one at https://mozilla.org/MPL/2.0/.
	;
	; SPDX-License-Identifier: MPL-2.0
	;