Add meetup exercise (#358)

.github/workflows/ci.yml

@@ -19,6 +19,9 @@ jobs:
           swi-prolog-branch: stable
           swi-prolog-version: latest
 
+      - name: Install packages
+        run: swipl pack install date_time -y
+
       - name: Verify all exercises
         run: bin/verify-exercises.sh
 

config.json

@@ -518,6 +518,14 @@
         "prerequisites": [],
         "difficulty": 1
       },
+      {
+        "slug": "meetup",
+        "name": "Meetup",
+        "uuid": "2590ef6c-3643-4d20-8f81-224d430ad3eb",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 1
+      },
       {
         "slug": "robot-simulator",
         "name": "Robot Simulator",

exercises/practice/meetup/.docs/hints.md

@@ -0,0 +1,9 @@
+# Hints
+
+## General
+
+- Use the [date_time package][date_time_package] to make working with dates a lot easier.
+- Check the [source of the date_time package][https://www.swi-prolog.org/pack/file_details/date_time/prolog/date_time.pl?show=src] for detailed information on how to use the package.
+
+[date_time_package]: https://www.swi-prolog.org/pack/list?p=date_time
+[date_time-package-source]: https://www.swi-prolog.org/pack/file_details/date_time/prolog/date_time.pl?show=src

exercises/practice/meetup/.docs/instructions.append.md

@@ -0,0 +1,40 @@
+# Instructions append
+
+## Working with Dates in Prolog
+
+Prolog's built-in support for dates is [fairly rudimentary][built-in-dates-support].
+A much nicer way to work with dates is via the [date_time package][date_time-package].
+
+### Installing the date_time package
+
+If your installed Swipl version is fairly up-to-date, you can install the package by running:
+
+```bash
+swipl pack install date_time
+```
+
+If that doesn't work, you can run:
+
+```shell
+swipl -g 'pack_install(date_time)'
+```
+
+~~~~exercism/note
+If you're using the online editor, you don't need to manually install anything.
+~~~~
+
+### Using the date_time package
+
+Ad the following code to the top of your solution file to use the `date_time` package:
+
+```prolog
+:- use_module(library(date_time)).
+```
+
+~~~~exercism/note
+Tip: the [source of the date_time package][https://www.swi-prolog.org/pack/file_details/date_time/prolog/date_time.pl?show=src] is well documented and be a great help!
+~~~~
+
+[built-in-dates-support]: https://www.swi-prolog.org/pldoc/man?section=timedate
+[date_time_package]: https://www.swi-prolog.org/pack/list?p=date_time
+[date_time-package-source]: https://www.swi-prolog.org/pack/file_details/date_time/prolog/date_time.pl?show=src

exercises/practice/meetup/.docs/instructions.md

@@ -0,0 +1,51 @@
+# Instructions
+
+Recurring monthly meetups are generally scheduled on the given weekday of a given week each month.
+In this exercise you will be given the recurring schedule, along with a month and year, and then asked to find the exact date of the meetup.
+
+For example a meetup might be scheduled on the _first Monday_ of every month.
+You might then be asked to find the date that this meetup will happen in January 2018.
+In other words, you need to determine the date of the first Monday of January 2018.
+
+Similarly, you might be asked to find:
+
+- the third Tuesday of August 2019 (August 20, 2019)
+- the teenth Wednesday of May 2020 (May 13, 2020)
+- the fourth Sunday of July 2021 (July 25, 2021)
+- the last Thursday of November 2022 (November 24, 2022)
+
+The descriptors you are expected to process are: `first`, `second`, `third`, `fourth`, `last`, `teenth`.
+
+Note that descriptor `teenth` is a made-up word.
+
+It refers to the seven numbers that end in '-teen' in English: 13, 14, 15, 16, 17, 18, and 19.
+But general descriptions of dates use ordinal numbers, e.g. the _first_ Monday, the _third_ Tuesday.
+
+For the numbers ending in '-teen', that becomes:
+
+- 13th (thirteenth)
+- 14th (fourteenth)
+- 15th (fifteenth)
+- 16th (sixteenth)
+- 17th (seventeenth)
+- 18th (eighteenth)
+- 19th (nineteenth)
+
+So there are seven numbers ending in '-teen'.
+And there are also seven weekdays (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday).
+Therefore, it is guaranteed that each day of the week (Monday, Tuesday, ...) will have exactly one numbered day ending with "teen" each month.
+
+If asked to find the teenth Saturday of August, 1953 (or, alternately the "Saturteenth" of August, 1953), we need to look at the calendar for August 1953:
+
+```plaintext
+    August 1953
+Su Mo Tu We Th Fr Sa
+                   1
+ 2  3  4  5  6  7  8
+ 9 10 11 12 13 14 15
+16 17 18 19 20 21 22
+23 24 25 26 27 28 29
+30 31
+```
+
+The Saturday that has a number ending in '-teen' is August 15, 1953.

exercises/practice/meetup/.meta/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": [
+    "erikschierboom"
+  ],
+  "files": {
+    "solution": [
+      "meetup.pl"
+    ],
+    "test": [
+      "meetup_tests.plt"
+    ],
+    "example": [
+      ".meta/meetup.example.pl"
+    ]
+  },
+  "blurb": "Calculate the date of meetups.",
+  "source": "Jeremy Hinegardner mentioned a Boulder meetup that happens on the Wednesteenth of every month"
+}

exercises/practice/meetup/.meta/meetup.example.pl

@@ -0,0 +1,34 @@
+:- use_module(library(date_time)).
+:- use_module(library(clpfd)).
+
+days_helper(Month, Date, WeekDay, Dates) :-
+    date_extract(Date, months(Month)),
+    date_add(Date, 1 days, NextDay),
+    days_helper(Month, NextDay, WeekDay, NextDates),
+    (week_day(Date, WeekDay) -> Dates = [Date|NextDates]; Dates = NextDates), !.
+
+days_helper(_, _, _, []).
+
+days(Year, Month, WeekDay, Dates) :-
+    date_create(Year, Month, 1, Date),
+    days_helper(Month, Date, WeekDay, Dates).
+
+nth1_day(Year, Month, WeekDay, Index, Date) :-
+    days(Year, Month, WeekDay, Dates),
+    nth1(Index, Dates, Date).
+
+meetup(Year, Month, first, WeekDay, Date)  :- nth1_day(Year, Month, WeekDay, 1, Date), !.
+meetup(Year, Month, second, WeekDay, Date) :- nth1_day(Year, Month, WeekDay, 2, Date), !.
+meetup(Year, Month, third, WeekDay, Date)  :- nth1_day(Year, Month, WeekDay, 3, Date), !.
+meetup(Year, Month, fourth, WeekDay, Date) :- nth1_day(Year, Month, WeekDay, 4, Date), !.
+
+meetup(Year, Month, last, WeekDay, Date) :-
+    days(Year, Month, WeekDay, Dates),
+    last(Dates, Date), !.
+
+meetup(Year, Month, teenth, WeekDay, Date) :-
+    days(Year, Month, WeekDay, Dates),
+    member(Date, Dates), 
+    date_extract(Date, days(Day)),
+    Day #>= 13,
+    !.