Add circular-buffer exercise (#95)

config.json

@@ -359,6 +359,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "521c505e-edb6-4a9c-82e8-44eed527e9ff",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "flatten-array",
         "name": "Flatten Array",

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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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/Example.roc

@@ -0,0 +1,41 @@
+module [create, read, write, overwrite, clear]
+
+CircularBuffer : { data : List I64, start : U64, length : U64 }
+
+create : { capacity : U64 } -> CircularBuffer
+create = \{ capacity } ->
+    { data: List.repeat 0 capacity, start: 0, length: 0 }
+
+read : CircularBuffer -> Result { newBuffer : CircularBuffer, value : I64 } [BufferEmpty]
+read = \{ data, start, length } ->
+    if length == 0 then
+        Err BufferEmpty
+    else
+        incrementStart = (start + 1) % List.len data
+        newBuffer = { data, start: incrementStart, length: length - 1 }
+        when data |> List.get start is
+            Ok value -> Ok { newBuffer, value }
+            Err OutOfBounds -> crash "Unreachable: start should never be out of bounds"
+
+write : CircularBuffer, I64 -> Result CircularBuffer [BufferFull]
+write = \{ data, start, length }, value ->
+    if length == List.len data then
+        Err BufferFull
+    else
+        index = (start + length) % List.len data
+        newData = data |> List.replace index value |> .list
+        Ok { data: newData, start, length: length + 1 }
+
+overwrite : CircularBuffer, I64 -> CircularBuffer
+overwrite = \{ data, start, length }, value ->
+    index = (start + length) % List.len data
+    newData = data |> List.replace index value |> .list
+    if length == List.len data then
+        incStart = (start + 1) % List.len data
+        { data: newData, start: incStart, length: length }
+    else
+        { data: newData, start, length: length + 1 }
+
+clear : CircularBuffer -> CircularBuffer
+clear = \circularBuffer ->
+    { data: circularBuffer.data, start: 0, length: 0 }

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "CircularBuffer.roc"
+    ],
+    "test": [
+      "circular-buffer-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "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/template.j2

@@ -0,0 +1,46 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+{{ macros.header() }}
+
+import {{ exercise | to_pascal }} exposing [create, read, write, overwrite, clear]
+
+{% for case in cases -%}
+# {{ case["description"] }}
+runOperations{{ loop.index }} =
+    result =
+        create { capacity: {{ case["input"]["capacity"] }} }
+        {%- for op in case["input"]["operations"] -%}
+        {%- if op["operation"] == "clear" %}
+        |> clear
+        {%- elif op["operation"] == "overwrite" %}
+        |> overwrite {{ op["item"] }}
+        {%- elif op["operation"] == "write" %}
+        {%- if op["should_succeed"] %}
+        |> write? {{ op["item"] }}
+        {%- else %}
+        |> \bufferBeforeWrite ->
+            writeResult = bufferBeforeWrite |> write {{ op["item"] }}
+            expect writeResult == Err BufferFull
+            bufferBeforeWrite
+        {%- endif %}
+        {%- elif op["operation"] == "read" %}
+        {%- if op["should_succeed"] %}
+        |> read? |> \readResult ->
+            expect readResult.value == {{ op["expected"] }}
+            readResult.newBuffer
+        {%- else %}
+        |> \bufferBeforeRead ->
+            readResult = bufferBeforeRead |> read
+            expect readResult == Err BufferEmpty
+            bufferBeforeRead
+        {%- endif %}
+        {%- endif %}
+        {%- endfor %}
+    Ok result
+
+expect
+
+    result = runOperations{{ loop.index }}
+    result |> Result.isOk
+
+{% endfor %}

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/CircularBuffer.roc

@@ -0,0 +1,23 @@
+module [create, read, write, overwrite, clear]
+
+CircularBuffer : { data : List I64, start : U64, length : U64 }
+
+create : { capacity : U64 } -> CircularBuffer
+create = \{ capacity } ->
+    crash "Please implement the 'create' function"
+
+read : CircularBuffer -> Result { newBuffer : CircularBuffer, value : I64 } [BufferEmpty]
+read = \{ data, start, length } ->
+    crash "Please implement the 'read' function"
+
+write : CircularBuffer, I64 -> Result CircularBuffer [BufferFull]
+write = \circularBuffer, value ->
+    crash "Please implement the 'write' function"
+
+overwrite : CircularBuffer, I64 -> CircularBuffer
+overwrite = \{ data, start, length }, value ->
+    crash "Please implement the 'overwrite' function"
+
+clear : CircularBuffer -> CircularBuffer
+clear = \circularBuffer ->
+    crash "Please implement the 'clear' function"