Add resistor-color exercise (#273)

config.json

@@ -394,6 +394,14 @@
         "difficulty": 1,
         "topics": []
       },
+      {
+        "slug": "resistor-color",
+        "name": "Resistor Color",
+        "uuid": "85f16b58-019f-44f7-bb33-b2903886f199",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 1
+      },
       {
         "slug": "rna-transcription",
         "name": "RNA Transcription",

exercises/practice/resistor-color/.docs/instructions.md

@@ -0,0 +1,39 @@
+# Instructions
+
+If you want to build something using a Raspberry Pi, you'll probably use _resistors_.
+For this exercise, you need to know two things about them:
+
+- Each resistor has a resistance value.
+- Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
+
+To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
+Each band has a position and a numeric value.
+
+The first 2 bands of a resistor have a simple encoding scheme: each color maps to a single number.
+
+In this exercise you are going to create a helpful program so that you don't have to remember the values of the bands.
+
+These colors are encoded as follows:
+
+- Black: 0
+- Brown: 1
+- Red: 2
+- Orange: 3
+- Yellow: 4
+- Green: 5
+- Blue: 6
+- Violet: 7
+- Grey: 8
+- White: 9
+
+The goal of this exercise is to create a way:
+
+- to look up the numerical value associated with a particular color band
+- to list the different band colors
+
+Mnemonics map the colors to the numbers, that, when stored as an array, happen to map to their index in the array:
+Better Be Right Or Your Great Big Values Go Wrong.
+
+More information on the color encoding of resistors can be found in the [Electronic color code Wikipedia article][e-color-code].
+
+[e-color-code]: https://en.wikipedia.org/wiki/Electronic_color_code

exercises/practice/resistor-color/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "resistor-color.sml"
+    ],
+    "test": [
+      "test.sml"
+    ],
+    "example": [
+      ".meta/example.sml"
+    ]
+  },
+  "blurb": "Convert a resistor band's color to its numeric representation.",
+  "source": "Maud de Vries, Erik Schierboom",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/1458"
+}

exercises/practice/resistor-color/.meta/example.sml

@@ -0,0 +1,14 @@
+val colors =
+  ["black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white"]
+
+fun colorCode (color: string) =
+  let
+    fun recurse (l: string list, index: int): int =
+      case l of
+          nil => raise Fail "invalid color"
+        | first :: rest =>
+            if first = color then index
+            else recurse (rest, index + 1)
+  in
+    recurse (colors, 0)
+  end

exercises/practice/resistor-color/.meta/tests.toml

@@ -0,0 +1,22 @@
+# 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.
+
+[49eb31c5-10a8-4180-9f7f-fea632ab87ef]
+description = "Color codes -> Black"
+
+[0a4df94b-92da-4579-a907-65040ce0b3fc]
+description = "Color codes -> White"
+
+[5f81608d-f36f-4190-8084-f45116b6f380]
+description = "Color codes -> Orange"
+
+[581d68fa-f968-4be2-9f9d-880f2fb73cf7]
+description = "Colors"

exercises/practice/resistor-color/resistor-color.sml

@@ -0,0 +1,5 @@
+fun colorCode color =
+  raise Fail "'colorCode' is not implemented"
+
+val colors: string list =
+  nil

exercises/practice/resistor-color/test.sml

@@ -0,0 +1,30 @@
+(* version 1.0.0 *)
+
+use "testlib.sml";
+use "resistor-color.sml";
+
+infixr |>
+fun x |> f = f x
+
+val testsuite =
+  describe "resistor-color" [
+    describe "Color codes" [
+      test "Black"
+        (fn _ => colorCode "black" |> Expect.equalTo 0),
+
+      test "White"
+        (fn _ => colorCode "white" |> Expect.equalTo 9),
+
+      test "Orange"
+        (fn _ => colorCode "orange" |> Expect.equalTo 3)
+    ],
+
+    test "Colors"
+      (fn _ => let
+        val expected = ["black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white"]
+      in
+        colors |> Expect.equalTo expected
+      end)
+  ]
+
+val _ = Test.run testsuite

exercises/practice/resistor-color/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)