add binary search exercise

.gitignore

@@ -9,3 +9,4 @@ node_modules
 
 tmp
 lib
+**/*.res.js

config.json

@@ -70,6 +70,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "binary-search",
+        "name": "Binary Search",
+        "uuid": "75286043-b11b-4653-bfe8-6854ef9fac23",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },

exercises/practice/acronym/.gitignore

@@ -1 +1,2 @@
-node_modules
+node_modules
+**/*.res.js

exercises/practice/acronym/package.json

@@ -18,7 +18,7 @@
   "scripts": {
     "res:build": "rescript",
     "res:start": "rescript build -w",
-    "test": "retest tmp/tests/*.js",
-    "ci": "npm run res:build && npm test"
+    "test": "rescript && retest **/tests/*.js",
+    "ci": "npm test"
   }
 }

exercises/practice/acronym/tests/Acronym_test.res

@@ -38,4 +38,3 @@ test("apostrophes", () => {
 test("underscore emphasis", () => {
   stringEqual(~message="underscore emphasis", abbreviate("The Road _Not_ Taken"), "TRNT")
 })
-

exercises/practice/binary-search/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Your task is to implement a binary search algorithm.
+
+A binary search algorithm finds an item in a list by repeatedly splitting it in half, only keeping the half which contains the item we're looking for.
+It allows us to quickly narrow down the possible locations of our item until we find it, or until we've eliminated all possible locations.
+
+~~~~exercism/caution
+Binary search only works when a list has been sorted.
+~~~~
+
+The algorithm looks like this:
+
+- Find the middle element of a _sorted_ list and compare it with the item we're looking for.
+- If the middle element is our item, then we're done!
+- If the middle element is greater than our item, we can eliminate that element and all the elements **after** it.
+- If the middle element is less than our item, we can eliminate that element and all the elements **before** it.
+- If every element of the list has been eliminated then the item is not in the list.
+- Otherwise, repeat the process on the part of the list that has not been eliminated.
+
+Here's an example:
+
+Let's say we're looking for the number 23 in the following sorted list: `[4, 8, 12, 16, 23, 28, 32]`.
+
+- We start by comparing 23 with the middle element, 16.
+- Since 23 is greater than 16, we can eliminate the left half of the list, leaving us with `[23, 28, 32]`.
+- We then compare 23 with the new middle element, 28.
+- Since 23 is less than 28, we can eliminate the right half of the list: `[23]`.
+- We've found our item.

exercises/practice/binary-search/.docs/introduction.md

@@ -0,0 +1,13 @@
+# Introduction
+
+You have stumbled upon a group of mathematicians who are also singer-songwriters.
+They have written a song for each of their favorite numbers, and, as you can imagine, they have a lot of favorite numbers (like [0][zero] or [73][seventy-three] or [6174][kaprekars-constant]).
+
+You are curious to hear the song for your favorite number, but with so many songs to wade through, finding the right song could take a while.
+Fortunately, they have organized their songs in a playlist sorted by the title — which is simply the number that the song is about.
+
+You realize that you can use a binary search algorithm to quickly find a song given the title.
+
+[zero]: https://en.wikipedia.org/wiki/0
+[seventy-three]: https://en.wikipedia.org/wiki/73_(number)
+[kaprekars-constant]: https://en.wikipedia.org/wiki/6174_(number)

exercises/practice/binary-search/.gitignore

@@ -0,0 +1,2 @@
+node_modules
+**/*.res.js

exercises/practice/binary-search/.meta/BinarySearch.res

@@ -0,0 +1,20 @@
+let find = (array: array<int>, value: int): option<int> => {
+  let rec go = (lo, hi) =>
+    if lo > hi {
+      None
+    } else {
+      let mid = lo + (hi - lo) / 2
+      // Use getUnsafe because our bounds logic ensures 'mid' is valid
+      let midVal = Array.getUnsafe(array, mid)
+
+      if midVal < value {
+        go(mid + 1, hi)
+      } else if midVal > value {
+        go(lo, mid - 1)
+      } else {
+        Some(mid)
+      }
+    }
+
+  go(0, Array.length(array) - 1)
+}

exercises/practice/binary-search/.meta/BinarySearch.resi

@@ -0,0 +1 @@
+let find: (array<int>, int) => option<int>

exercises/practice/binary-search/.meta/config.json

@@ -0,0 +1,24 @@
+{
+  "authors": [
+    "stevejb71",
+    "therealowenrees"
+  ],
+  "files": {
+    "solution": [
+      "src/BinarySearch.res"
+    ],
+    "test": [
+      "tests/BinarySearch_test.res"
+    ],
+    "example": [
+      ".meta/BinarySearch.res",
+      ".meta/BinarySearch.resi"
+    ],
+    "editor": [
+      "src/BinarySearch.resi"
+    ]
+  },
+  "blurb": "Implement a binary search algorithm.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Binary_search_algorithm"
+}

exercises/practice/binary-search/.meta/testTemplate.js

@@ -0,0 +1,26 @@
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { assertEqual } from "../../../../test_generator/assertions.js";
+import { generateTests } from '../../../../test_generator/testGenerator.js';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const slug = path.basename(path.resolve(__dirname, '..'))
+
+// EDIT THIS WITH YOUR ASSERTIONS
+export const assertionFunctions = [ assertEqual ]
+
+// EDIT THIS WITH YOUR TEST TEMPLATES
+export const template = (c) => {
+  const { array, value } = c.input
+  const expected = c.expected
+
+  const arrayStr = `[${array.join(', ')}]`
+
+  const expectedStr = (typeof expected === 'number')
+    ? `Some(${expected})`
+    : "None"
+
+  return `assertEqual(~message="${c.description}", find(${arrayStr}, ${value}), ${expectedStr})`
+}
+
+generateTests(__dirname, slug, assertionFunctions, template)

exercises/practice/binary-search/.meta/tests.toml

@@ -0,0 +1,43 @@
+# 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.
+
+[b55c24a9-a98d-4379-a08c-2adcf8ebeee8]
+description = "finds a value in an array with one element"
+
+[73469346-b0a0-4011-89bf-989e443d503d]
+description = "finds a value in the middle of an array"
+
+[327bc482-ab85-424e-a724-fb4658e66ddb]
+description = "finds a value at the beginning of an array"
+
+[f9f94b16-fe5e-472c-85ea-c513804c7d59]
+description = "finds a value at the end of an array"
+
+[f0068905-26e3-4342-856d-ad153cadb338]
+description = "finds a value in an array of odd length"
+
+[fc316b12-c8b3-4f5e-9e89-532b3389de8c]
+description = "finds a value in an array of even length"
+
+[da7db20a-354f-49f7-a6a1-650a54998aa6]
+description = "identifies that a value is not included in the array"
+
+[95d869ff-3daf-4c79-b622-6e805c675f97]
+description = "a value smaller than the array's smallest value is not found"
+
+[8b24ef45-6e51-4a94-9eac-c2bf38fdb0ba]
+description = "a value larger than the array's largest value is not found"
+
+[f439a0fa-cf42-4262-8ad1-64bf41ce566a]
+description = "nothing is found in an empty array"
+
+[2c353967-b56d-40b8-acff-ce43115eed64]
+description = "nothing is found when the left and right bounds cross"

exercises/practice/binary-search/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Exercism
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.