Elm: isograms

config.json

@@ -332,6 +332,16 @@
         "Lists",
         "Control-flow"
       ]
+    },
+    {
+      "uuid": "5f540090-061e-2f80-40a8-d9782700ed2efdf8965",
+      "slug": "isogram",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 3,
+      "topics": [
+        "Lists"
+      ]
     }
   ],
   "foregone": [

exercises/isogram/Isogram.elm

@@ -0,0 +1 @@
+module Isogram exposing (..)

exercises/isogram/Isogram.example.elm

@@ -0,0 +1,76 @@
+module Isogram exposing (isIsogram)
+
+import String
+import List
+import Char
+
+
+isLetter : Char -> Bool
+isLetter c =
+    Char.isHexDigit c && (not <| Char.isDigit c)
+
+
+isIsogram : String -> Bool
+isIsogram sentence =
+    let
+        sanitized =
+            String.filter isLetter sentence
+                |> String.toLower
+                |> String.toList
+                |> List.sort
+                |> group
+    in
+        List.all (\x -> List.length x == 1) sanitized
+
+
+
+-- Adapted from https://github.com/elm-community/list-extra
+
+
+group : List a -> List (List a)
+group list =
+    case list of
+        [] ->
+            []
+
+        x :: xs ->
+            let
+                ( ys, zs ) =
+                    span ((==) x) xs
+            in
+                (x :: ys) :: group zs
+
+
+span : (a -> Bool) -> List a -> ( List a, List a )
+span p xs =
+    ( takeWhile p xs, dropWhile p xs )
+
+
+takeWhile : (a -> Bool) -> List a -> List a
+takeWhile predicate =
+    let
+        takeWhileHelper acc list =
+            case list of
+                [] ->
+                    List.reverse acc
+
+                x :: xs ->
+                    if (predicate x) then
+                        takeWhileHelper (x :: acc) xs
+                    else
+                        List.reverse acc
+    in
+        takeWhileHelper []
+
+
+dropWhile : (a -> Bool) -> List a -> List a
+dropWhile predicate list =
+    case list of
+        [] ->
+            []
+
+        x :: xs ->
+            if (predicate x) then
+                dropWhile predicate xs
+            else
+                list

exercises/isogram/README.md

@@ -0,0 +1,50 @@
+# Isogram
+
+Determine if a word or phrase is an isogram.
+
+An isogram (also known as a "nonpattern word") is a word or phrase without a repeating letter, however spaces and hyphens are allowed to appear multiple times.
+
+Examples of isograms:
+
+- lumberjacks
+- background
+- downstream
+- six-year-old
+
+The word *isograms*, however, is not an isogram, because the s repeats.
+
+## Elm Installation
+
+Refer to the [Exercism help page](http://exercism.io/languages/elm) for Elm
+installation and learning resources.
+
+## Writing the Code
+
+The first time you start an exercise, you'll need to ensure you have the
+appropriate dependencies installed.
+
+```bash
+$ npm install
+```
+
+Execute the tests with:
+
+```bash
+$ npm test
+```
+
+Automatically run tests again when you save changes:
+
+```bash
+$ npm run watch
+```
+
+As you work your way through the test suite, be sure to remove the `skip <|`
+calls from each test until you get them all passing!
+
+## Source
+
+Wikipedia [https://en.wikipedia.org/wiki/Isogram](https://en.wikipedia.org/wiki/Isogram)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/isogram/elm-package.json

@@ -0,0 +1,14 @@
+{
+    "version": "3.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/elm.git",
+    "license": "BSD3",
+    "source-directories": [
+        "."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "elm-lang/core": "5.0.0 <= v < 6.0.0"
+    },
+    "elm-version": "0.18.0 <= v < 0.19.0"
+}

exercises/isogram/package.json

@@ -0,0 +1,14 @@
+{
+    "description": "Exercism/Elm",
+    "repository": "https://github.com/exercism/elm.git",
+    "license": "MIT",
+    "scripts": {
+        "postinstall": "elm-package install -y",
+        "watch": "elm-test --watch",
+        "test": "elm-test"
+    },
+    "dependencies": {
+        "elm": "0.18.0",
+        "elm-test": "0.18.3"
+    }
+}

exercises/isogram/tests/Tests.elm

@@ -0,0 +1,38 @@
+module Tests exposing (..)
+
+import Test exposing (..)
+import Expect
+import Isogram exposing (isIsogram)
+
+
+tests : Test
+tests =
+    describe "Isogram"
+        [ test "empty string" <|
+            \() ->
+                Expect.equal True <| isIsogram ""
+        , test "isogram with only lower case characters" <|
+            \() ->
+                Expect.equal True <| isIsogram "isogram"
+        , test "word with one duplicated character" <|
+            \() ->
+                Expect.equal False <| isIsogram "eleven"
+        , test "longest reported english isogram" <|
+            \() ->
+                Expect.equal True <| isIsogram "subdermatoglyphic"
+        , test "word with duplicated character in mixed case" <|
+            \() ->
+                Expect.equal False <| isIsogram "Alphabet"
+        , test "hypothetical isogrammic word with hyphen" <|
+            \() ->
+                Expect.equal True <| isIsogram "thumbscrew-japingly"
+        , test "isogram with duplicated non letter character" <|
+            \() ->
+                Expect.equal True <| isIsogram "Hjelmqvist-Gryb-Zock-Pfund-Wax"
+        , test "made-up name that is an isogram" <|
+            \() ->
+                Expect.equal True <| isIsogram "Emily Jung Schwartzkopf"
+        , test "duplicated character in the middle" <|
+            \() ->
+                Expect.equal False <| isIsogram "accentor"
+        ]

exercises/isogram/tests/elm-package.json

@@ -0,0 +1,16 @@
+{
+    "version": "3.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/elm.git",
+    "license": "BSD3",
+    "source-directories": [
+        ".",
+        ".."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "elm-lang/core": "5.0.0 <= v < 6.0.0",
+        "elm-community/elm-test": "4.0.0 <= v < 5.0.0"
+    },
+    "elm-version": "0.18.0 <= v < 0.19.0"
+}