New exercise (do not merge)

exercises/practice/meetup2/.config/dotnet-tools.json

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+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "fantomas-tool": {
+      "version": "3.2.0",
+      "commands": [
+        "fantomas"
+      ]
+    }
+  }
+}

exercises/practice/meetup2/.docs/instructions.md

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+# 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/meetup2/.meta/Example.fs

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+module Meetup
+
+open System
+
+type Week = First | Second | Third | Fourth | Last | Teenth
+
+let meetup year month week dayOfWeek = 
+    let daysOfWeek = 
+        [1 .. DateTime.DaysInMonth(year, month)]
+        |> List.map (fun day -> DateTime(year, month, day))
+        |> List.filter (fun date -> date.DayOfWeek = dayOfWeek)
+
+    match week with
+    | Week.First  -> daysOfWeek |> List.item 0
+    | Week.Second -> daysOfWeek |> List.item 1
+    | Week.Third  -> daysOfWeek |> List.item 2
+    | Week.Fourth -> daysOfWeek |> List.item 3
+    | Week.Last   -> daysOfWeek |> List.last 
+    | Week.Teenth -> daysOfWeek |> List.find (fun date -> date.Day >= 13)

exercises/practice/meetup2/.meta/config.json

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+{
+  "authors": [
+    "ErikSchierboom"
+  ],
+  "contributors": [
+    "jrr",
+    "lestephane",
+    "robkeim",
+    "valentin-p",
+    "wolf99"
+  ],
+  "files": {
+    "solution": [
+      "Meetup.fs"
+    ],
+    "test": [
+      "MeetupTests.fs"
+    ],
+    "example": [
+      ".meta/Example.fs"
+    ],
+    "invalidator": [
+      "Meetup.fsproj"
+    ]
+  },
+  "blurb": "Calculate the date of meetups.",
+  "source": "Jeremy Hinegardner mentioned a Boulder meetup that happens on the Wednesteenth of every month",
+  "source_url": "http://www.copiousfreetime.org/"
+}