add roman numerals (#39)

* exercise boilerplate

* generate test cases

* example solution to pass tests

Author: TheRealOwenRees

config.json

@@ -157,6 +157,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "roman-numerals",
+        "name": "Roman Numerals",
+        "uuid": "11463a13-d10e-4a06-9063-977266ad706e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "rotational-cipher",
         "name": "Rotational Cipher",

exercises/practice/roman-numerals/.docs/instructions.md

@@ -0,0 +1,12 @@
+# Introduction
+
+Your task is to convert a number from Arabic numerals to Roman numerals.
+
+For this exercise, we are only concerned about traditional Roman numerals, in which the largest number is MMMCMXCIX (or 3,999).
+
+~~~~exercism/note
+There are lots of different ways to convert between Arabic and Roman numerals.
+We recommend taking a naive approach first to familiarise yourself with the concept of Roman numerals and then search for more efficient methods.
+
+Make sure to check out our Deep Dive video at the end to explore the different approaches you can take!
+~~~~

exercises/practice/roman-numerals/.docs/introduction.md

@@ -0,0 +1,59 @@
+# Description
+
+Today, most people in the world use Arabic numerals (0–9).
+But if you travelled back two thousand years, you'd find that most Europeans were using Roman numerals instead.
+
+To write a Roman numeral we use the following Latin letters, each of which has a value:
+
+| M    | D   | C   | L   | X   | V   | I   |
+| ---- | --- | --- | --- | --- | --- | --- |
+| 1000 | 500 | 100 | 50  | 10  | 5   | 1   |
+
+A Roman numeral is a sequence of these letters, and its value is the sum of the letters' values.
+For example, `XVIII` has the value 18 (`10 + 5 + 1 + 1 + 1 = 18`).
+
+There's one rule that makes things trickier though, and that's that **the same letter cannot be used more than three times in succession**.
+That means that we can't express numbers such as 4 with the seemingly natural `IIII`.
+Instead, for those numbers, we use a subtraction method between two letters.
+So we think of `4` not as `1 + 1 + 1 + 1` but instead as `5 - 1`.
+And slightly confusingly to our modern thinking, we write the smaller number first.
+This applies only in the following cases: 4 (`IV`), 9 (`IX`), 40 (`XL`), 90 (`XC`), 400 (`CD`) and 900 (`CM`).
+
+Order matters in Roman numerals!
+Letters (and the special compounds above) must be ordered by decreasing value from left to right.
+
+Here are some examples:
+
+```text
+ 105 => CV
+---- => --
+ 100 => C
++  5 =>  V
+```
+
+```text
+ 106 => CVI
+---- => --
+ 100 => C
++  5 =>  V
++  1 =>   I
+```
+
+```text
+ 104 => CIV
+---- => ---
+ 100 => C
++  4 =>  IV
+```
+
+And a final more complex example:
+
+```text
+ 1996 => MCMXCVI
+----- => -------
+ 1000 => M
++ 900 =>  CM
++  90 =>    XC
++   5 =>      V
++   1 =>       I
+```

exercises/practice/roman-numerals/.gitignore

@@ -0,0 +1,2 @@
+node_modules
+**/*.res.js

exercises/practice/roman-numerals/.meta/RomanNumerals.res

@@ -0,0 +1,21 @@
+let roman = n => {
+  let rec aux = (s, remainder) => {
+    switch remainder {
+    | r if r >= 1000 => aux(s ++ "M", r - 1000)
+    | r if r >= 900 => aux(s ++ "CM", r - 900)
+    | r if r >= 500 => aux(s ++ "D", r - 500)
+    | r if r >= 400 => aux(s ++ "CD", r - 400)
+    | r if r >= 100 => aux(s ++ "C", r - 100)
+    | r if r >= 90 => aux(s ++ "XC", r - 90)
+    | r if r >= 50 => aux(s ++ "L", r - 50)
+    | r if r >= 40 => aux(s ++ "XL", r - 40)
+    | r if r >= 10 => aux(s ++ "X", r - 10)
+    | r if r >= 9 => aux(s ++ "IX", r - 9)
+    | r if r >= 5 => aux(s ++ "V", r - 5)
+    | r if r >= 4 => aux(s ++ "IV", r - 4)
+    | r if r >= 1 => aux(s ++ "I", r - 1)
+    | _ => s
+    }
+  }
+  aux("", n)
+}

exercises/practice/roman-numerals/.meta/RomanNumerals.resi

@@ -0,0 +1 @@
+let roman: int => string

exercises/practice/roman-numerals/.meta/config.json

@@ -0,0 +1,21 @@
+{
+  "authors": [
+    "therealowenrees"
+  ],
+  "files": {
+    "solution": [
+      "src/RomanNumerals.res",
+      "src/RomanNumerals.resi"
+    ],
+    "test": [
+      "tests/RomanNumerals_test.res"
+    ],
+    "example": [
+      ".meta/RomanNumerals.res",
+      ".meta/RomanNumerals.resi"
+    ]
+  },
+  "blurb": "Convert modern Arabic numbers into Roman numerals.",
+  "source": "The Roman Numeral Kata",
+  "source_url": "https://codingdojo.org/kata/RomanNumerals/"
+}

exercises/practice/roman-numerals/.meta/tests.toml

@@ -0,0 +1,91 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[19828a3a-fbf7-4661-8ddd-cbaeee0e2178]
+description = "1 is I"
+
+[f088f064-2d35-4476-9a41-f576da3f7b03]
+description = "2 is II"
+
+[b374a79c-3bea-43e6-8db8-1286f79c7106]
+description = "3 is III"
+
+[05a0a1d4-a140-4db1-82e8-fcc21fdb49bb]
+description = "4 is IV"
+
+[57c0f9ad-5024-46ab-975d-de18c430b290]
+description = "5 is V"
+
+[20a2b47f-e57f-4797-a541-0b3825d7f249]
+description = "6 is VI"
+
+[ff3fb08c-4917-4aab-9f4e-d663491d083d]
+description = "9 is IX"
+
+[6d1d82d5-bf3e-48af-9139-87d7165ed509]
+description = "16 is XVI"
+
+[2bda64ca-7d28-4c56-b08d-16ce65716cf6]
+description = "27 is XXVII"
+
+[a1f812ef-84da-4e02-b4f0-89c907d0962c]
+description = "48 is XLVIII"
+
+[607ead62-23d6-4c11-a396-ef821e2e5f75]
+description = "49 is XLIX"
+
+[d5b283d4-455d-4e68-aacf-add6c4b51915]
+description = "59 is LIX"
+
+[4465ffd5-34dc-44f3-ada5-56f5007b6dad]
+description = "66 is LXVI"
+
+[46b46e5b-24da-4180-bfe2-2ef30b39d0d0]
+description = "93 is XCIII"
+
+[30494be1-9afb-4f84-9d71-db9df18b55e3]
+description = "141 is CXLI"
+
+[267f0207-3c55-459a-b81d-67cec7a46ed9]
+description = "163 is CLXIII"
+
+[902ad132-0b4d-40e3-8597-ba5ed611dd8d]
+description = "166 is CLXVI"
+
+[cdb06885-4485-4d71-8bfb-c9d0f496b404]
+description = "402 is CDII"
+
+[6b71841d-13b2-46b4-ba97-dec28133ea80]
+description = "575 is DLXXV"
+
+[dacb84b9-ea1c-4a61-acbb-ce6b36674906]
+description = "666 is DCLXVI"
+
+[432de891-7fd6-4748-a7f6-156082eeca2f]
+description = "911 is CMXI"
+
+[e6de6d24-f668-41c0-88d7-889c0254d173]
+description = "1024 is MXXIV"
+
+[efbe1d6a-9f98-4eb5-82bc-72753e3ac328]
+description = "1666 is MDCLXVI"
+
+[bb550038-d4eb-4be2-a9ce-f21961ac3bc6]
+description = "3000 is MMM"
+
+[3bc4b41c-c2e6-49d9-9142-420691504336]
+description = "3001 is MMMI"
+
+[2f89cad7-73f6-4d1b-857b-0ef531f68b7e]
+description = "3888 is MMMDCCCLXXXVIII"
+
+[4e18e96b-5fbb-43df-a91b-9cb511fe0856]
+description = "3999 is MMMCMXCIX"

exercises/practice/roman-numerals/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Exercism
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.