Plisp / nwhen

A simple calendar program using a Lisp domain language.

nwhen

nwhen is a simple calendar program that introduces a domain-specific language written in Lisp for its calendar files. The name is inspired by Ben Crowell's when program, as nvim is to vim.

; Specify events like this:
(event "Lunch with Ben" :year 2021 :month :january :day 5)
; You can specify the date in any order.
(event "Save the world" :month july :day 4 :year 2025)
; If you leave out a date field, the event will repeat.
(event "Amelia's Birthday" :day 5 :month :august) ; This repeats every August 5
; There is a shortcut function for birthdays.
(birthday "Thomas" :day 29 :month :november)

; To avoid repetition, you can create 'scopes' like the following
(year 2021
  (month :january
    (event "Canoeing" :day 5)          ; Implies 2021-01-05
    (event "Hiking with Mum" :day 14)) ; Implies 2021-01-14
  (month :february
    (event "Physics Exam" :day 2)))    ; Implies 2021-02-02

; You can separate your calendar amongst multiple files with the include
; function. Paths are always relative to NWHEN_HOME.
(include "birthdays")
(include "exams")

By default, nwhen tries to open $HOME/calendar as the calendar file. This behaviour can be configured by setting the NWHEN_HOME environment variable.

This is my first significant Lisp program, so code review is appreicated.

Arbitrary Code Execution

The contents of the calendar file are executed as a Common Lisp program, enabling calendar entries that have dates that must be algorithmically calculated each year. I hope to illustrate this with the following example of Mother's Day. In most countries that celebrate Mother's Day, it occurs on the second Sunday of May.

(let ((mothers-day (nth 1 (remove-if-not (lambda (date)
                                           (and (eq (getf date :month) :may)
                                                (dow-eq (getf date :dow) :sun)))
                                         *time-span*))))
  (when mothers-day
    (push (append mothers-day '(:desc "Mother's Day")) *unqualified-events*)))

Chinese Lunisolar Calendar Dates

nwhen has limited support for Chinese lunisolar calendar dates, currently in a very unoptimal way. It must call a Python script that depends upon Wei Yen's lunisolar library. This feature is not well-tested in the slightest, and is likely flawed! Please do not use this in production.

(birthday "Grandpa" :month 5 :day 12 chinese t)

License

nwhen is licensed under the BSD 2-Clause "Simplified" License.