Add ocr-numbers exercises (#152)

* Add ocr-numbers exercises
* Use early return syntax as suggested by Isaac

config.json

@@ -595,6 +595,14 @@
         "prerequisites": [],
         "difficulty": 4
       },
+      {
+        "slug": "ocr-numbers",
+        "name": "OCR Numbers",
+        "uuid": "e4d5e487-e017-4a3b-8338-28920d7d5a01",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "perfect-numbers",
         "name": "Perfect Numbers",

exercises/practice/ocr-numbers/.docs/instructions.md

@@ -0,0 +1,79 @@
+# Instructions
+
+Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.
+
+## Step One
+
+To begin with, convert a simple binary font to a string containing 0 or 1.
+
+The binary font uses pipes and underscores, four rows high and three columns wide.
+
+```text
+     _   #
+    | |  # zero.
+    |_|  #
+         # the fourth row is always blank
+```
+
+Is converted to "0"
+
+```text
+         #
+      |  # one.
+      |  #
+         # (blank fourth row)
+```
+
+Is converted to "1"
+
+If the input is the correct size, but not recognizable, your program should return '?'
+
+If the input is the incorrect size, your program should return an error.
+
+## Step Two
+
+Update your program to recognize multi-character binary strings, replacing garbled numbers with ?
+
+## Step Three
+
+Update your program to recognize all numbers 0 through 9, both individually and as part of a larger string.
+
+```text
+ _
+ _|
+|_
+
+```
+
+Is converted to "2"
+
+```text
+      _  _     _  _  _  _  _  _  #
+    | _| _||_||_ |_   ||_||_|| | # decimal numbers.
+    ||_  _|  | _||_|  ||_| _||_| #
+                                 # fourth line is always blank
+```
+
+Is converted to "1234567890"
+
+## Step Four
+
+Update your program to handle multiple numbers, one per line.
+When converting several lines, join the lines with commas.
+
+```text
+    _  _
+  | _| _|
+  ||_  _|
+
+    _  _
+|_||_ |_
+  | _||_|
+
+ _  _  _
+  ||_||_|
+  ||_| _|
+
+```
+
+Is converted to "123,456,789".

exercises/practice/ocr-numbers/.meta/Example.roc

@@ -0,0 +1,72 @@
+module [convert]
+
+BadGridSize : [HeightWasNotAMultipleOf4, WidthWasNotAMultipleOf3, GridShapeWasNotRectangular]
+
+convert : Str -> Result Str BadGridSize
+convert = \grid ->
+    if grid == "" then
+        Ok ""
+        else
+
+    gridChars = grid |> Str.split "\n" |> List.map Str.toUtf8
+    size = checkSize? gridChars
+    gridChars
+    |> List.chunksOf 4 # split vertically into groups of 4 rows
+    |> List.map \rowGroup ->
+        getDigitGrids rowGroup size.width
+        |> List.map identifyDigit
+        |> Str.joinWith ""
+    |> Str.joinWith ","
+    |> Ok
+
+checkSize : List (List U8) -> Result { height : U64, width : U64 } BadGridSize
+checkSize = \gridChars ->
+    height = List.len gridChars
+    if height % 4 != 0 then
+        Err HeightWasNotAMultipleOf4
+        else
+
+    width = gridChars |> List.map List.len |> List.max |> Result.withDefault 0
+    if width % 3 != 0 then
+        Err WidthWasNotAMultipleOf3
+        else
+
+    isRectangular = gridChars |> List.all \row -> List.len row == width
+    if isRectangular then
+        Ok { height, width }
+    else
+        Err GridShapeWasNotRectangular
+
+## Given four rows from the full grid, return the 3x4 grid for each digit
+getDigitGrids : List (List U8), U64 -> List (List (List U8))
+getDigitGrids = \rowGroup, fullGridWidth ->
+    chunkedRows =
+        rowGroup
+        |> List.map \row ->
+            row |> List.chunksOf 3
+    numHorizontalChunks = fullGridWidth // 3
+    List.range { start: At 0, end: Before numHorizontalChunks }
+    |> List.map \chunkIndex ->
+        chunkedRows
+        |> List.map \chunkedRow ->
+            when chunkedRow |> List.get chunkIndex is
+                Ok chunk -> chunk
+                Err OutOfBounds -> crash "Unreachable: we checked the grid size"
+
+identifyDigit : List (List U8) -> Str
+identifyDigit = \digitGrid ->
+    #  _     _  _     _  _  _  _  _
+    # | |  | _| _||_||_ |_   ||_||_|
+    # |_|  ||_  _|  | _||_|  ||_| _|
+    when digitGrid is
+        [[' ', '_', ' '], ['|', ' ', '|'], ['|', '_', '|'], [' ', ' ', ' ']] -> "0"
+        [[' ', ' ', ' '], [' ', ' ', '|'], [' ', ' ', '|'], [' ', ' ', ' ']] -> "1"
+        [[' ', '_', ' '], [' ', '_', '|'], ['|', '_', ' '], [' ', ' ', ' ']] -> "2"
+        [[' ', '_', ' '], [' ', '_', '|'], [' ', '_', '|'], [' ', ' ', ' ']] -> "3"
+        [[' ', ' ', ' '], ['|', '_', '|'], [' ', ' ', '|'], [' ', ' ', ' ']] -> "4"
+        [[' ', '_', ' '], ['|', '_', ' '], [' ', '_', '|'], [' ', ' ', ' ']] -> "5"
+        [[' ', '_', ' '], ['|', '_', ' '], ['|', '_', '|'], [' ', ' ', ' ']] -> "6"
+        [[' ', '_', ' '], [' ', ' ', '|'], [' ', ' ', '|'], [' ', ' ', ' ']] -> "7"
+        [[' ', '_', ' '], ['|', '_', '|'], ['|', '_', '|'], [' ', ' ', ' ']] -> "8"
+        [[' ', '_', ' '], ['|', '_', '|'], [' ', '_', '|'], [' ', ' ', ' ']] -> "9"
+        _ -> "?"

exercises/practice/ocr-numbers/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "OcrNumbers.roc"
+    ],
+    "test": [
+      "ocr-numbers-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "blurb": "Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.",
+  "source": "Inspired by the Bank OCR kata",
+  "source_url": "https://codingdojo.org/kata/BankOCR/"
+}

exercises/practice/ocr-numbers/.meta/template.j2

@@ -0,0 +1,19 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+{{ macros.header() }}
+
+import {{ exercise | to_pascal }} exposing [{{ cases[0]["property"] | to_camel }}]
+
+{% for case in cases -%}
+# {{ case["description"] }}
+expect
+    grid = {{ case["input"]["rows"] | to_roc_multiline_string | indent(8) }}
+    result = {{ case["property"] | to_camel }} grid
+    {%- if case["expected"]["error"] %}
+    result |> Result.isErr
+    {%- else %}
+    expected = Ok {{ case["expected"] | to_roc }}
+    result == expected
+    {%- endif %}
+
+{% endfor %}

exercises/practice/ocr-numbers/.meta/tests.toml

@@ -0,0 +1,61 @@
+# 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.
+
+[5ee54e1a-b554-4bf3-a056-9a7976c3f7e8]
+description = "Recognizes 0"
+
+[027ada25-17fd-4d78-aee6-35a19623639d]
+description = "Recognizes 1"
+
+[3cce2dbd-01d9-4f94-8fae-419a822e89bb]
+description = "Unreadable but correctly sized inputs return ?"
+
+[cb19b733-4e36-4cf9-a4a1-6e6aac808b9a]
+description = "Input with a number of lines that is not a multiple of four raises an error"
+
+[235f7bd1-991b-4587-98d4-84206eec4cc6]
+description = "Input with a number of columns that is not a multiple of three raises an error"
+
+[4a841794-73c9-4da9-a779-1f9837faff66]
+description = "Recognizes 110101100"
+
+[70c338f9-85b1-4296-a3a8-122901cdfde8]
+description = "Garbled numbers in a string are replaced with ?"
+
+[ea494ff4-3610-44d7-ab7e-72fdef0e0802]
+description = "Recognizes 2"
+
+[1acd2c00-412b-4268-93c2-bd7ff8e05a2c]
+description = "Recognizes 3"
+
+[eaec6a15-be17-4b6d-b895-596fae5d1329]
+description = "Recognizes 4"
+
+[440f397a-f046-4243-a6ca-81ab5406c56e]
+description = "Recognizes 5"
+
+[f4c9cf6a-f1e2-4878-bfc3-9b85b657caa0]
+description = "Recognizes 6"
+
+[e24ebf80-c611-41bb-a25a-ac2c0f232df5]
+description = "Recognizes 7"
+
+[b79cad4f-e264-4818-9d9e-77766792e233]
+description = "Recognizes 8"
+
+[5efc9cfc-9227-4688-b77d-845049299e66]
+description = "Recognizes 9"
+
+[f60cb04a-42be-494e-a535-3451c8e097a4]
+description = "Recognizes string of decimal numbers"
+
+[b73ecf8b-4423-4b36-860d-3710bdb8a491]
+description = "Numbers separated by empty lines are recognized. Lines are joined by commas."

exercises/practice/ocr-numbers/OcrNumbers.roc

@@ -0,0 +1,5 @@
+module [convert]
+
+convert : Str -> Result Str _
+convert = \grid ->
+    crash "Please implement the 'convert' function"