calendar-code2 + a Clojure port

This repository echeran/calendar-code2 is a fork of the original repository for the Common Lisp code that is featured in the book Calendrical Calculations: The Ultimate Edition by Edward M. Reingold and Nachum Dershowitz (2018). Please refer to the book for the full details of each function that is provided.

This repository provides a Clojure port of the Common Lisp code, allowing an easy-to-use setup in which all of the code works as intended.

Why?

Despite having all of the original Common Lisp code at hand, it is not possible to get it run "out of the box" (see prior discussion). Updating the code to get it to run correctly is a non-trivial task.

Clojure is a modern dialect of Lisp with good tooling, documentation, and a wide platform reach. This allows us to achieve an easy setup experience for the language and the project's dependencies.

Other benefits:

• Having a running version of the book's functions allows us to validate / debug other calendar implementations' outputs by introspecting on helper functions
• We have easy access to computations for calendars that are not yet implemented elsewhere
• If needed to run on other platforms, we can use reader conditionals to make the code simultaneously compile to JavaScript and the CLR. For example, a webpage could run the Clojurescript (Javascript) code of all the functions locally.
• If we need more precision, we could replace +, -, and * in the Clojure code with the type-promoting versions +', -', and *' that give us BigInteger and Clojure's fixed-up version of BigDecimal when the precision of 64-bit types long and double are exceeded.

Using the code

All of the code's symbols (functions, constants) are currently available in the clj-calcalc.core namespace. You should be able to invoke any function you need while in this namespace.

Examples

;; In case your REPL does not automatically start in the `clj-calcaclc.core` namespace
user> (ns clj-calcalc.core)

;; Define some fixed dates used in the book's Appendix C of sample data
clj-calcalc.core> (def rd-vec [-214193 -61387 25469 49217])
#'clj-calcalc.core/rd-vec

;; Matches the column "Ephemeris Correction" in Appendix C sample data
clj-calcalc.core> (->> rd-vec
                       (map ephemeris-correction))
(0.21416985185185175
 0.14363257367091617
 0.11444429141515931
 0.10718320232694657)

;; Matches the column "Solar Longitude at 12:00:00 U.T. (Degrees)" in Appendix C sample data
clj-calcalc.core> (->> rd-vec
                       (map #(+ % 0.5))
                       (map solar-longitude))
(119.47343190503307
 254.2489611345809
 181.43599673954304
 188.66392267483752)

;; Matches the column "Islamic > Arithmetic" in Appendix C sample data
clj-calcalc.core> (->> rd-vec
                       (map islamic-from-fixed))
((-1245 12 9) (-813 2 23) (-568 4 1) (-501 4 6))

;; Matches the column "Chinese > Next Zhongqi" in Appendex C sample data
clj-calcalc.core> (->> rd-vec
                       (map major-solar-term-on-or-after))
(-214191.6331339299
 -61370.72967338959
 25498.215092247046
 49239.00486039391)

Setup instructions

There are a few ways to build Clojure projects. This project will provide instructions for all such supported tools, which are:

• Leiningen

Common setup prerequisites

You must have Java installed on your system. All versions of Clojure so far support Java 6+.

You will also need a project build tool.

Leiningen

Setup

The setup for Leiningen is straightforward if you are familiar with using Linux/Unix/Windows at the command line. Follow instructions at the homepage (https://leiningen.org/) to download the script that both installs and runs the tool.

Running lein for the first time will download the dependencies for Leiningen and likely the latest version of Clojure.

Running a REPL

Loading a REPL only requires moving into the Clojure code's project directory and issuing a REPL command to Leiningen:

cd calendar-code2/clj/clj-calcalc
lein repl

More info

Enjoy! Feel free to report issues of any errors, or if possible, open pull requests that make the fixes.