Add isogram exercise (#531)

Author: kahgoh

config.json

@@ -557,6 +557,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "isogram",
+        "name": "Isogram",
+        "uuid": "fe419d81-481d-49af-8e24-80defb0692f2",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

exercises/practice/isogram/.docs/instructions.md

@@ -0,0 +1,14 @@
+# Instructions
+
+Determine if a word or phrase is an isogram.
+
+An isogram (also known as a "non-pattern 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.

exercises/practice/isogram/.meta/config.json

@@ -0,0 +1,22 @@
+{
+  "authors": [
+    "kahgoh"
+  ],
+  "files": {
+    "solution": [
+      "isogram.ml"
+    ],
+    "test": [
+      "test.ml"
+    ],
+    "example": [
+      ".meta/example.ml"
+    ],
+    "editor": [
+      "isogram.mli"
+    ]
+  },
+  "blurb": "Determine if a word or phrase is an isogram.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Isogram"
+}

exercises/practice/isogram/.meta/example.ml

@@ -0,0 +1,15 @@
+let tail (word: string) = 
+  String.sub word 1 ((String.length word) - 1)
+
+let rec is_unique (ch: char) (word: string) : bool =
+  match (ch, word) with
+  | (_, "") -> true
+  | (c, w) when c < 'a' || c > 'z' -> is_unique (String.get w 0) (tail w)
+  | (c, w) when (String.contains w c) -> false 
+  | (_, w) -> is_unique (String.get w 0) (tail w)
+
+let is_isogram (word: string) : bool =
+  let lower_word = String.lowercase_ascii word in
+  match lower_word with
+  | "" -> true
+  | w -> is_unique(String.get w 0) (tail w)

exercises/practice/isogram/.meta/tests.toml

@@ -0,0 +1,52 @@
+# 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.
+
+[a0e97d2d-669e-47c7-8134-518a1e2c4555]
+description = "empty string"
+
+[9a001b50-f194-4143-bc29-2af5ec1ef652]
+description = "isogram with only lower case characters"
+
+[8ddb0ca3-276e-4f8b-89da-d95d5bae78a4]
+description = "word with one duplicated character"
+
+[6450b333-cbc2-4b24-a723-0b459b34fe18]
+description = "word with one duplicated character from the end of the alphabet"
+
+[a15ff557-dd04-4764-99e7-02cc1a385863]
+description = "longest reported english isogram"
+
+[f1a7f6c7-a42f-4915-91d7-35b2ea11c92e]
+description = "word with duplicated character in mixed case"
+
+[14a4f3c1-3b47-4695-b645-53d328298942]
+description = "word with duplicated character in mixed case, lowercase first"
+
+[423b850c-7090-4a8a-b057-97f1cadd7c42]
+description = "hypothetical isogrammic word with hyphen"
+
+[93dbeaa0-3c5a-45c2-8b25-428b8eacd4f2]
+description = "hypothetical word with duplicated character following hyphen"
+
+[36b30e5c-173f-49c6-a515-93a3e825553f]
+description = "isogram with duplicated hyphen"
+
+[cdabafa0-c9f4-4c1f-b142-689c6ee17d93]
+description = "made-up name that is an isogram"
+
+[5fc61048-d74e-48fd-bc34-abfc21552d4d]
+description = "duplicated character in the middle"
+
+[310ac53d-8932-47bc-bbb4-b2b94f25a83e]
+description = "same first and last characters"
+
+[0d0b8644-0a1e-4a31-a432-2b3ee270d847]
+description = "word with duplicated character and with two hyphens"

exercises/practice/isogram/Makefile

@@ -0,0 +1,9 @@
+default: clean test
+
+test: 
+	dune runtest
+
+clean:
+	dune clean
+
+.PHONY: clean

exercises/practice/isogram/dune

@@ -0,0 +1,16 @@
+(executable
+ (name test)
+ (libraries base ounit2))
+
+(alias
+  (name    runtest)
+  (deps    (:x test.exe))
+  (action  (run %{x})))
+
+(alias
+  (name    buildtest)
+  (deps    (:x test.exe)))
+
+(env
+  (dev
+    (flags (:standard -warn-error -A))))

exercises/practice/isogram/dune-project

@@ -0,0 +1,2 @@
+(lang dune 1.1)
+(version 1.0)

exercises/practice/isogram/isogram.ml

@@ -0,0 +1,2 @@
+let is_isogram (word: string) : bool =
+    failwith "'is_isogram' is missing" 

exercises/practice/isogram/isogram.mli

@@ -0,0 +1 @@
+val is_isogram : string -> bool