Add armstrong-numbers exercise

config.json

@@ -287,6 +287,17 @@
           "math"
         ]
       },
+      {
+        "slug": "armstrong-numbers",
+        "name": "Armstrong Numbers",
+        "uuid": "e1131c5f-f0a1-4cce-aa24-6fb4e265824a",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2,
+        "topics": [
+          "math"
+        ]
+      },
       {
         "slug": "pop-count",
         "name": "Pop Count",

exercises/practice/armstrong-numbers/.docs/instructions.md

@@ -0,0 +1,14 @@
+# Instructions
+
+An [Armstrong number][armstrong-number] is a number that is the sum of its own digits each raised to the power of the number of digits.
+
+For example:
+
+- 9 is an Armstrong number, because `9 = 9^1 = 9`
+- 10 is _not_ an Armstrong number, because `10 != 1^2 + 0^2 = 1`
+- 153 is an Armstrong number, because: `153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`
+- 154 is _not_ an Armstrong number, because: `154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`
+
+Write some code to determine whether a number is an Armstrong number.
+
+[armstrong-number]: https://en.wikipedia.org/wiki/Narcissistic_number

exercises/practice/armstrong-numbers/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "armstrong-numbers.sml"
+    ],
+    "test": [
+      "test.sml"
+    ],
+    "example": [
+      ".meta/example.sml"
+    ]
+  },
+  "blurb": "Determine if a number is an Armstrong number.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Narcissistic_number"
+}

exercises/practice/armstrong-numbers/.meta/example.sml

@@ -0,0 +1,26 @@
+local
+  fun recurse (exponent: int) (base: int) (multiplier: int): int =
+    if exponent = 0 then multiplier
+    else recurse (exponent div 2) (base * base) (if exponent mod 2 = 0 then multiplier else base * multiplier)
+in
+  fun power (exponent: int) (base: int): int =
+    recurse exponent base 1
+end
+
+fun isArmstrongNumber (number: int): bool =
+  let
+    val sum: int list -> int =
+      foldl op+ 0
+
+    fun recurse (digits: int list) (n: int): bool =
+      if n = 0 then
+        let
+          val count = length digits
+        in
+          number = sum (map (power count) digits)
+        end
+      else
+        recurse ((n mod 10) :: digits) (n div 10)
+  in
+    recurse [] number
+  end

exercises/practice/armstrong-numbers/.meta/tests.toml

@@ -0,0 +1,45 @@
+# 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.
+
+[c1ed103c-258d-45b2-be73-d8c6d9580c7b]
+description = "Zero is an Armstrong number"
+
+[579e8f03-9659-4b85-a1a2-d64350f6b17a]
+description = "Single-digit numbers are Armstrong numbers"
+
+[2d6db9dc-5bf8-4976-a90b-b2c2b9feba60]
+description = "There are no two-digit Armstrong numbers"
+
+[509c087f-e327-4113-a7d2-26a4e9d18283]
+description = "Three-digit number that is an Armstrong number"
+
+[7154547d-c2ce-468d-b214-4cb953b870cf]
+description = "Three-digit number that is not an Armstrong number"
+
+[6bac5b7b-42e9-4ecb-a8b0-4832229aa103]
+description = "Four-digit number that is an Armstrong number"
+
+[eed4b331-af80-45b5-a80b-19c9ea444b2e]
+description = "Four-digit number that is not an Armstrong number"
+
+[f971ced7-8d68-4758-aea1-d4194900b864]
+description = "Seven-digit number that is an Armstrong number"
+
+[7ee45d52-5d35-4fbd-b6f1-5c8cd8a67f18]
+description = "Seven-digit number that is not an Armstrong number"
+
+[5ee2fdf8-334e-4a46-bb8d-e5c19c02c148]
+description = "Armstrong number containing seven zeroes"
+include = false
+
+[12ffbf10-307a-434e-b4ad-c925680e1dd4]
+description = "The largest and last Armstrong number"
+include = false

exercises/practice/armstrong-numbers/armstrong-numbers.sml

@@ -0,0 +1,2 @@
+fun isArmstrongNumber (number: int): bool =
+  raise Fail "'isArmstrongNumber' is not implemented"

exercises/practice/armstrong-numbers/test.sml

@@ -0,0 +1,39 @@
+(* version 1.0.0 *)
+
+use "testlib.sml";
+use "armstrong-numbers.sml";
+
+infixr |>
+fun x |> f = f x
+
+val testsuite =
+  describe "armstrong-numbers" [
+    test "Zero is an Armstrong number"
+      (fn _ => isArmstrongNumber 0 |> Expect.truthy),
+
+    test "Single-digit numbers are Armstrong numbers"
+      (fn _ => isArmstrongNumber 5 |> Expect.truthy),
+
+    test "There are no two-digit Armstrong numbers"
+      (fn _ => isArmstrongNumber 10 |> Expect.falsy),
+
+    test "Three-digit number that is an Armstrong number"
+      (fn _ => isArmstrongNumber 153 |> Expect.truthy),
+
+    test "Three-digit number that is not an Armstrong number"
+      (fn _ => isArmstrongNumber 100 |> Expect.falsy),
+
+    test "Four-digit number that is an Armstrong number"
+      (fn _ => isArmstrongNumber 9474 |> Expect.truthy),
+
+    test "Four-digit number that is not an Armstrong number"
+      (fn _ => isArmstrongNumber 9475 |> Expect.falsy),
+
+    test "Seven-digit number that is an Armstrong number"
+      (fn _ => isArmstrongNumber 9926315 |> Expect.truthy),
+
+    test "Seven-digit number that is not an Armstrong number"
+      (fn _ => isArmstrongNumber 9926314 |> Expect.falsy)
+  ]
+
+val _ = Test.run testsuite

exercises/practice/armstrong-numbers/testlib.sml

@@ -0,0 +1,160 @@
+structure Expect =
+struct
+  datatype expectation = Pass | Fail of string * string
+
+  local
+    fun failEq b a =
+      Fail ("Expected: " ^ b, "Got: " ^ a)
+
+    fun failExn b a =
+      Fail ("Expected: " ^ b, "Raised: " ^ a)
+
+    fun exnName (e: exn): string = General.exnName e
+  in
+    fun truthy a =
+      if a
+      then Pass
+      else failEq "true" "false"
+
+    fun falsy a =
+      if a
+      then failEq "false" "true"
+      else Pass
+
+    fun equalTo b a = 
+      if a = b
+      then Pass
+      else failEq (PolyML.makestring b) (PolyML.makestring a)
+
+    fun nearTo delta b a =
+      if Real.abs (a - b) <= delta * Real.abs a orelse
+         Real.abs (a - b) <= delta * Real.abs b
+      then Pass
+      else failEq (Real.toString b ^ " +/- " ^ Real.toString delta) (Real.toString a)
+
+    fun anyError f =
+      (
+        f ();
+        failExn "an exception" "Nothing"
+      ) handle _ => Pass
+
+    fun error e f =
+      (
+        f ();
+        failExn (exnName e) "Nothing"
+      ) handle e' => if exnMessage e' = exnMessage e
+                     then Pass
+                     else failExn (exnMessage e) (exnMessage e')
+  end
+end
+
+structure TermColor =
+struct
+  datatype color = Red | Green | Yellow | Normal
+
+  fun f Red    = "\027[31m"
+    | f Green  = "\027[32m"
+    | f Yellow = "\027[33m"
+    | f Normal = "\027[0m"
+
+  fun colorize color s = (f color) ^ s ^ (f Normal)
+
+  val redit = colorize Red
+
+  val greenit = colorize Green
+
+  val yellowit = colorize Yellow
+end
+
+structure Test =
+struct
+  datatype testnode = TestGroup of string * testnode list
+                    | Test of string * (unit -> Expect.expectation)
+
+  local
+    datatype evaluation = Success of string
+                        | Failure of string * string * string
+                        | Error of string * string
+
+    fun indent n s = (implode (List.tabulate (n, fn _ => #" "))) ^ s
+
+    fun fmt indentlvl ev =
+      let
+        val check = TermColor.greenit "\226\156\148 " (* ✔ *)
+        val cross = TermColor.redit "\226\156\150 "   (* ✖ *)
+        val indentlvl = indentlvl * 2
+      in
+      case ev of
+        Success descr => indent indentlvl (check ^ descr)
+      | Failure (descr, exp, got) =>
+          String.concatWith "\n" [indent indentlvl (cross ^ descr),
+                                  indent (indentlvl + 2) exp,
+                                  indent (indentlvl + 2) got]
+      | Error (descr, reason) =>
+          String.concatWith "\n" [indent indentlvl (cross ^ descr),
+                                  indent (indentlvl + 2) (TermColor.redit reason)]
+      end
+
+    fun eval (TestGroup _) = raise Fail "Only a 'Test' can be evaluated"
+      | eval (Test (descr, thunk)) =
+          (
+            case thunk () of
+              Expect.Pass   => ((1, 0, 0), Success descr)
+            | Expect.Fail (s, s') => ((0, 1, 0), Failure (descr, s, s'))
+          )
+          handle e => ((0, 0, 1), Error (descr, "Unexpected error: " ^ exnMessage e))
+
+    fun flatten depth testnode =
+      let
+        fun sum (x, y, z) (a, b, c) = (x + a, y + b, z + c)
+
+        fun aux (t, (counter, acc)) =
+          let
+            val (counter', texts) = flatten (depth + 1) t
+          in
+            (sum counter' counter, texts :: acc)
+          end
+      in
+        case testnode of
+          TestGroup (descr, ts) =>
+            let
+              val (counter, texts) = foldr aux ((0, 0, 0), []) ts
+            in
+              (counter, (indent (depth * 2) descr) :: List.concat texts)
+            end
+        | Test _ =>
+            let
+              val (counter, evaluation) = eval testnode
+            in
+              (counter, [fmt depth evaluation])
+            end
+      end
+
+    fun println s = print (s ^ "\n")
+  in
+    fun run suite =
+      let
+        val ((succeeded, failed, errored), texts) = flatten 0 suite
+
+        val summary = String.concatWith ", " [
+          TermColor.greenit ((Int.toString succeeded) ^ " passed"),
+          TermColor.redit ((Int.toString failed) ^ " failed"),
+          TermColor.redit ((Int.toString errored) ^ " errored"),
+          (Int.toString (succeeded + failed + errored)) ^ " total"
+        ]
+
+        val status = if failed = 0 andalso errored = 0
+                     then OS.Process.success
+                     else OS.Process.failure
+
+      in
+        List.app println texts;
+        println "";
+        println ("Tests: " ^ summary);
+        OS.Process.exit status
+      end
+  end
+end
+
+fun describe description tests = Test.TestGroup (description, tests)
+fun test description thunk = Test.Test (description, thunk)