Add triangle exercise (closes #30)

config.json

@@ -15,7 +15,8 @@
      "run-length-encoding",
      "difference-of-squares",
      "anagram",
-     "raindrops"
+     "raindrops",
+     "triangle"
   ],
   "deprecated": [
 

elm-package.json

@@ -15,7 +15,8 @@
         "./exercises/run-length-encoding",
         "./exercises/difference-of-squares",
         "./exercises/anagram",
-        "./exercises/raindrops"
+        "./exercises/raindrops",
+        "./exercises/triangle"
     ],
     "exposed-modules": [],
     "dependencies": {

exercises/triangle/Triangle.elm

@@ -0,0 +1 @@
+module Triangle (..) where

exercises/triangle/Triangle.example

@@ -0,0 +1,21 @@
+module Triangle (..) where
+
+import Set
+
+
+triangleKind : number -> number -> number -> Result String String
+triangleKind x y z =
+  if x <= 0 || y <= 0 || z <= 0 then
+    Err "Invalid lengths"
+  else if x + y <= z || x + z <= y || y + z <= x then
+    Err "Violates inequality"
+  else
+    case Set.size (Set.fromList [ x, y, z ]) of
+      1 ->
+        Ok "equilateral"
+
+      2 ->
+        Ok "isosceles"
+
+      _ ->
+        Ok "scalene"

exercises/triangle/TriangleTests.elm

@@ -0,0 +1,63 @@
+module Main (..) where
+
+import Task
+import Console
+import ElmTest exposing (..)
+import Triangle exposing (triangleKind)
+
+
+tests : Test
+tests =
+  suite
+    "triangleKind"
+    [ test
+        "equilateral triangles have equal sides"
+        (assertEqual (Ok "equilateral") (triangleKind 2 2 2))
+    , test
+        "larger equilateral triangles also have equal sides"
+        (assertEqual (Ok "equilateral") (triangleKind 10 10 10))
+    , test
+        "isosceles triangles have last two sides equal"
+        (assertEqual (Ok "isosceles") (triangleKind 3 4 4))
+    , test
+        "isosceles triangles have first and last sides equal"
+        (assertEqual (Ok "isosceles") (triangleKind 4 3 4))
+    , test
+        "isosceles triangles have two first sides equal"
+        (assertEqual (Ok "isosceles") (triangleKind 4 4 3))
+    , test
+        "isosceles triangles have in fact exactly two sides equal"
+        (assertEqual (Ok "isosceles") (triangleKind 10 10 2))
+    , test
+        "scalene triangles have no equal sides"
+        (assertEqual (Ok "scalene") (triangleKind 3 4 5))
+    , test
+        "scalene triangles have no equal sides at a larger scale too"
+        (assertEqual (Ok "scalene") (triangleKind 10 11 12))
+    , test
+        "scalene triangles have no equal sides at a larger scale too 2"
+        (assertEqual (Ok "scalene") (triangleKind 5 4 2))
+    , test
+        "very small triangles are legal"
+        (assertEqual (Ok "scalene") (triangleKind 0.4 0.6 0.3))
+    , test
+        "triangles with no size are illegal"
+        (assertEqual (Err "Invalid lengths") (triangleKind 0 0 0))
+    , test
+        "triangles with negative sides are illegal"
+        (assertEqual (Err "Invalid lengths") (triangleKind 3 4 -5))
+    , test
+        "triangles violating triangle inequality are illegal 1"
+        (assertEqual (Err "Violates inequality") (triangleKind 1 1 3))
+    , test
+        "triangles violating triangle inequality are illegal 2"
+        (assertEqual (Err "Violates inequality") (triangleKind 2 4 2))
+    , test
+        "triangles violating triangle inequality are illegal 3"
+        (assertEqual (Err "Violates inequality") (triangleKind 7 3 2))
+    ]
+
+
+port runner : Signal (Task.Task x ())
+port runner =
+  Console.run (consoleRunner tests)

exercises/triangle/elm-package.json

@@ -0,0 +1,16 @@
+{
+    "version": "1.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/xelm.git",
+    "license": "BSD3",
+    "source-directories": [
+        "."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "deadfoxygrandpa/elm-test": "3.0.1 <= v < 4.0.0",
+        "elm-lang/core": "2.0.0 <= v < 4.0.0",
+        "laszlopandy/elm-console": "1.1.0 <= v < 2.0.0"
+    },
+    "elm-version": "0.15.0 <= v < 0.17.0"
+}