Add circular buffer

config.json

@@ -103,6 +103,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "512d263f-b3ce-4f5a-ba43-6b05a2b5c0f5",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "clock",
         "name": "Clock",

exercises/practice/circular-buffer/.docs/instructions.md

@@ -0,0 +1,58 @@
+# Instructions
+
+A circular buffer, cyclic buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end.
+
+A circular buffer first starts empty and of some predefined length.
+For example, this is a 7-element buffer:
+
+```text
+[ ][ ][ ][ ][ ][ ][ ]
+```
+
+Assume that a 1 is written into the middle of the buffer (exact starting location does not matter in a circular buffer):
+
+```text
+[ ][ ][ ][1][ ][ ][ ]
+```
+
+Then assume that two more elements are added — 2 & 3 — which get appended after the 1:
+
+```text
+[ ][ ][ ][1][2][3][ ]
+```
+
+If two elements are then removed from the buffer, the oldest values inside the buffer are removed.
+The two elements removed, in this case, are 1 & 2, leaving the buffer with just a 3:
+
+```text
+[ ][ ][ ][ ][ ][3][ ]
+```
+
+If the buffer has 7 elements then it is completely full:
+
+```text
+[5][6][7][8][9][3][4]
+```
+
+When the buffer is full an error will be raised, alerting the client that further writes are blocked until a slot becomes free.
+
+When the buffer is full, the client can opt to overwrite the oldest data with a forced write.
+In this case, two more elements — A & B — are added and they overwrite the 3 & 4:
+
+```text
+[5][6][7][8][9][A][B]
+```
+
+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.
+Finally, if two elements are removed then what would be returned is 5 & 6 yielding the buffer:
+
+```text
+[ ][ ][7][8][9][A][B]
+```
+
+Because there is space available, if the client again uses overwrite to store C & D then the space where 5 & 6 were stored previously will be used not the location of 7 & 8.
+7 is still the oldest element and the buffer is once again full.
+
+```text
+[C][D][7][8][9][A][B]
+```

exercises/practice/circular-buffer/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "circular-buffer.arr"
+    ],
+    "test": [
+      "circular-buffer-test.arr"
+    ],
+    "example": [
+      ".meta/example.arr"
+    ]
+  },
+  "blurb": "A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Circular_buffer"
+}

exercises/practice/circular-buffer/.meta/example.arr

@@ -0,0 +1,43 @@
+use context essentials2020 # Don't delete this line when using Pyret on Exercism 
+
+data CircularBuffer:
+  | buffer(capacity :: Number, size :: Number, elements, read-index :: Number, write-index :: Number)
+    with:
+    method write(self, value :: Number) block:
+      when self.size == self.capacity:
+        raise(“full buffer”)
+      end
+      self.elements.set-now(self.write-index, value)
+      buffer(self.capacity,
+        self.size + 1,
+        self.elements,
+        self.read-index,
+        num-modulo(self.read-index + 1, self.capacity))
+    end,
+    method read(self) block:
+      when self.size == 0:
+        raise(“empty buffer”)
+      end
+      val = self.elements.get-now(self.read-index)
+      updated = buffer(self.capacity,
+        self.size - 1,
+        self.elements,
+        num-modulo(self.read-index + 1, self.capacity),
+        self.write-index)
+    {val;updated}
+    end,
+    method overwrite(self, value :: Number) block:
+      buff = if self.size == self.capacity:
+        self.read().{1}
+      else:
+        self
+      end
+      buff.write(value)
+    end,
+    method clear(self):
+      make-buffer(self.capacity)
+    end
+end
+fun make-buffer(capacity :: Number):
+    buffer(capacity, 0, array-of(none, capacity), 0, 0)
+end

exercises/practice/circular-buffer/.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.
+
+[28268ed4-4ff3-45f3-820e-895b44d53dfa]
+description = "reading empty buffer should fail"
+
+[2e6db04a-58a1-425d-ade8-ac30b5f318f3]
+description = "can read an item just written"
+
+[90741fe8-a448-45ce-be2b-de009a24c144]
+description = "each item may only be read once"
+
+[be0e62d5-da9c-47a8-b037-5db21827baa7]
+description = "items are read in the order they are written"
+
+[2af22046-3e44-4235-bfe6-05ba60439d38]
+description = "full buffer can't be written to"
+
+[547d192c-bbf0-4369-b8fa-fc37e71f2393]
+description = "a read frees up capacity for another write"
+
+[04a56659-3a81-4113-816b-6ecb659b4471]
+description = "read position is maintained even across multiple writes"
+
+[60c3a19a-81a7-43d7-bb0a-f07242b1111f]
+description = "items cleared out of buffer can't be read"
+
+[45f3ae89-3470-49f3-b50e-362e4b330a59]
+description = "clear frees up capacity for another write"
+
+[e1ac5170-a026-4725-bfbe-0cf332eddecd]
+description = "clear does nothing on empty buffer"
+
+[9c2d4f26-3ec7-453f-a895-7e7ff8ae7b5b]
+description = "overwrite acts like write on non-full buffer"
+
+[880f916b-5039-475c-bd5c-83463c36a147]
+description = "overwrite replaces the oldest item on full buffer"
+
+[bfecab5b-aca1-4fab-a2b0-cd4af2b053c3]
+description = "overwrite replaces the oldest item remaining in buffer following a read"
+
+[9cebe63a-c405-437b-8b62-e3fdc1ecec5a]
+description = "initial clear does not affect wrapping around"

exercises/practice/circular-buffer/circular-buffer-test.arr

@@ -0,0 +1,140 @@
+use context essentials2020
+
+include file("circular-buffer.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 read-empty-buffer-should-fail():
+  check "reading empty buffer should fail":
+    make-buffer(1).read() raises "empty buffer"
+  end
+end
+
+fun can-read-an-item-just-written():
+  check "can read an item just written":
+    make-buffer(1).write(1).read() is 1
+  end
+end
+
+fun each-item-may-only-be-read-once():
+  check "each item may only be read once":
+    results = make-buffer(1).write(1).read()
+    results.{0} is 1
+    results.{1}.read() raises "empty buffer"
+  end
+end
+
+fun items-are-read-in-the-order-they-are-written():
+  check "items are read in the order they are written":
+    var results = make-buffer(2).write(1).write(2).read()
+    results.{0} is 1
+    results = results.{1}.read()
+    results.{0} is 2
+  end
+end
+
+fun full-buffer-can-not-be-written-to():
+  check "full buffer can't be written to":
+    make-buffer(1).write(1).write(2) raises "full buffer"
+  end
+end
+
+fun a-read-frees-up-capacity-for-another-write():
+  check "a read frees up capacity for another write":
+    var results = make-buffer(1).write(1).read()
+    results.{0} is 1
+    results = results.{1}.write(2).read()
+    results.{0} is 2
+  end
+end
+
+fun read-position-is-maintained-even-across-multiple-writes():
+  check "read position is maintained even across multiple writes":
+    var results = make-buffer(3).write(1).write(2).read()
+    results.{0} is 1
+    results = results.{1}.write(3).read()
+    results.{0} is 2
+    results = results.{1}.read()
+    results.{0} is 3
+  end
+end
+
+fun items-cleared-out-of-buffer-can-not-be-read():
+  check "items cleared out of buffer can't be read":
+    results = make-buffer(1).write(1).clear()
+    results.read() raises "empty buffer"
+  end
+end
+
+fun clear-frees-up-capacity-for-another-write():
+  check "clear frees up capacity for another write":
+    results = make-buffer(1).write(1).clear().write(2)
+    results.read() is 2
+  end
+end
+
+fun clear-does-nothing-on-empty-buffer():
+  check "clear does nothing on empty buffer":
+    results = make-buffer(1).clear().write(1)
+    results.read() is 1
+  end
+end
+
+fun overwrite-acts-like-write-on-non-full-buffer():
+  check "overwrite acts like write on non-full buffer":
+    ...
+  end
+end
+
+fun overwrite-replaces-the-oldest-item-on-full-buffer():
+  check "overwrite replaces the oldest item on full buffer":
+    ...
+  end
+end
+
+fun overwrite-replaces-the-oldest-item-remaining-in-buffer-following-a-read():
+  check "overwrite replaces the oldest item remaining in buffer following a read":
+    ...
+  end
+end
+
+fun initial-clear-does-not-affect-wrapping-around():
+  check "initial clear does not affect wrapping around":
+    ...
+  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(read-empty-buffer-should-fail, true),
+  test(can-read-an-item-just-written, false),
+  test(each-item-may-only-be-read-once, false),
+  test(items-are-read-in-the-order-they-are-written, false),
+  test(full-buffer-can-not-be-written-to, false),
+  test(a-read-frees-up-capacity-for-another-write, false),
+  test(read-position-is-maintained-even-across-multiple-writes, false),
+  test(items-cleared-out-of-buffer-can-not-be-read, false),
+  test(clear-frees-up-capacity-for-another-write, false),
+  test(clear-does-nothing-on-empty-buffer, false),
+  test(overwrite-acts-like-write-on-non-full-buffer, false),
+  test(overwrite-replaces-the-oldest-item-on-full-buffer, false),
+  test(overwrite-replaces-the-oldest-item-remaining-in-buffer-following-a-read, false),
+  test(initial-clear-does-not-affect-wrapping-around, false),
+  test(zero-steps-for-one, true),
+  test(divide-if-even, false),
+  test(even-and-odd-steps, false),
+  test(large-number-of-even-and-odd-steps, false),
+  test(zero-is-an-error, false),
+  test(negative-is-an-error, false)
+].each(lam(t): when t.active: t.run() end end)

exercises/practice/circular-buffer/circular-buffer.arr

@@ -0,0 +1 @@
+use context essentials2020 # Don't delete this line when using Pyret on Exercism