Add pop-count exercise (#157)

config.json

@@ -291,6 +291,16 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "pop-count",
+        "name": "Pop Count",
+        "uuid": "ebfaddfb-d094-4471-8771-fc09cf14274f",
+        "practices": [
+          "numbers"
+        ],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "protein-translation",
         "name": "Protein Translation",

exercises/practice/pop-count/.docs/instructions.md

@@ -0,0 +1,8 @@
+# Instructions
+
+Your task is to count the number of 1 bits in the binary representation of a number.
+
+## Restrictions
+
+Keep your hands off that bit-count functionality provided by your standard library!
+Solve this one yourself using other basic tools instead.

exercises/practice/pop-count/.docs/introduction.md

@@ -0,0 +1,47 @@
+# Introduction
+
+Your friend Eliud inherited a farm from her grandma Tigist.
+Her granny was an inventor and had a tendency to build things in an overly complicated manner.
+The chicken coop has a digital display showing an encoded number representing the positions of all eggs that could be picked up.
+
+Eliud is asking you to write a program that shows the actual number of eggs in the coop.
+
+The position information encoding is calculated as follows:
+
+1. Scan the potential egg-laying spots and mark down a `1` for an existing egg or a `0` for an empty spot.
+2. Convert the number from binary to decimal.
+3. Show the result on the display.
+
+Example 1:
+
+```text
+Chicken Coop:
+ _ _ _ _ _ _ _
+|E| |E|E| | |E|
+
+Resulting Binary:
+ 1 0 1 1 0 0 1
+
+Decimal number on the display:
+89
+
+Actual eggs in the coop:
+4
+```
+
+Example 2:
+
+```text
+Chicken Coop:
+ _ _ _ _ _ _ _ _
+| | | |E| | | | |
+
+Resulting Binary:
+ 0 0 0 1 0 0 0 0
+
+Decimal number on the display:
+16
+
+Actual eggs in the coop:
+1
+```

exercises/practice/pop-count/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "pop-count.arr"
+    ],
+    "test": [
+      "pop-count-test.arr"
+    ],
+    "example": [
+      ".meta/example.arr"
+    ]
+  },
+  "blurb": "Count the 1 bits in a number",
+  "source": "Christian Willner, Eric Willigers",
+  "source_url": "https://forum.exercism.org/t/new-exercise-suggestion-pop-count/7632/5"
+}

exercises/practice/pop-count/.meta/example.arr

@@ -0,0 +1,17 @@
+use context essentials2020
+
+provide: egg-count end
+
+fun egg-count(n):
+  fun recurse(val, eggs):
+    if val == 0:
+      eggs
+    else if num-is-positive(num-modulo(val, 2)):
+      recurse(num-truncate(val / 2), eggs + 1)
+    else:
+      recurse(num-truncate(val / 2), eggs)
+    end
+  end
+
+  recurse(n, 0)
+end

exercises/practice/pop-count/.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.
+
+[559e789d-07d1-4422-9004-3b699f83bca3]
+description = "0 eggs"
+
+[97223282-f71e-490c-92f0-b3ec9e275aba]
+description = "1 egg"
+
+[1f8fd18f-26e9-4144-9a0e-57cdfc4f4ff5]
+description = "4 eggs"
+
+[0c18be92-a498-4ef2-bcbb-28ac4b06cb81]
+description = "13 eggs"

exercises/practice/pop-count/pop-count-test.arr

@@ -0,0 +1,48 @@
+use context essentials2020
+
+include file("pop-count.arr")
+
+#|
+  When working offline, all tests except the first one are skipped by default.
+  Once you get the first test running, unskip the next one until all tests pass locally.
+  Check the block comment below for further details.
+|#
+
+fun zero-eggs():
+  check "0 eggs":
+    egg-count(0) is 0
+  end
+end
+
+fun one-egg():
+  check "1 egg":
+    egg-count(16) is 1
+  end
+end
+
+fun four-eggs():
+  check "4 eggs":
+    egg-count(89) is 4
+  end
+end
+
+fun thirteen-eggs():
+  check "13 eggs":
+    egg-count(2000000000) is 13
+  end
+end
+
+#|
+  Code to run each test. Each line corresponds to a test above and whether it should be run.
+  To mark a test to be run, replace `false` with `true` on that same line after the comma.
+  test(test-a, true) will be run. test(test-a, false) will be skipped.
+|#
+
+data TestRun: test(run, active) end
+
+[list: 
+  test(zero-eggs, true),
+  test(one-egg, false),
+  test(four-eggs, false),
+  test(thirteen-eggs, false)
+].each(lam(t): when t.active: t.run() end end)

exercises/practice/pop-count/pop-count.arr

@@ -0,0 +1,7 @@
+use context essentials2020 # Don't delete this line when using Pyret on Exercism 
+
+provide: egg-count end
+
+fun egg-count(n):
+  raise("Please implement the egg-count function")
+end