Add hexadecimal exercise

config.json

@@ -135,6 +135,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "hexadecimal",
+        "name": "Hexadecimal",
+        "uuid": "e63a6404-5e3a-41bc-b8bd-9a91b6513bf4",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "isogram",
         "name": "Isogram",

exercises/practice/hexadecimal/.docs/instructions.md

@@ -0,0 +1,7 @@
+# Instructions
+
+Convert a hexadecimal number, represented as a string (e.g. "10af8c"), to its decimal equivalent using first principles (i.e. no, you may not use built-in or external libraries to accomplish the conversion).
+
+On the web we use hexadecimal to represent colors, e.g. green: 008000, teal: 008080, navy: 000080).
+
+The program should handle invalid hexadecimal strings.

exercises/practice/hexadecimal/.meta/Example.roc

@@ -0,0 +1,23 @@
+module [parse]
+
+parseNibble = \char ->
+    when char is
+        c if c >= '0' && c <= '9' -> Ok (c - '0' |> Num.toU64)
+        c if c >= 'A' && c <= 'F' -> Ok (c - 'A' + 10 |> Num.toU64)
+        c if c >= 'a' && c <= 'f' -> Ok (c - 'a' + 10 |> Num.toU64)
+        _ -> Err InvalidNumStr
+
+parse : Str -> Result U64 _
+parse = \string ->
+    if string == "" then
+        Err InvalidNumStr
+        else
+
+    string
+        |> Str.toUtf8
+        |> List.walkTry 0 \number, char ->
+            nibble = parseNibble? char
+            if number > 0xfffffffffffffff then
+                Err InvalidNumStr
+            else
+                number |> Num.shiftLeftBy 4 |> Num.add nibble |> Ok

exercises/practice/hexadecimal/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "Hexadecimal.roc"
+    ],
+    "test": [
+      "hexadecimal-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "blurb": "Convert a hexadecimal number, represented as a string (e.g. \"10af8c\"), to its decimal equivalent using first principles (i.e. no, you may not use built-in or external libraries to accomplish the conversion).",
+  "source": "All of Computer Science",
+  "source_url": "https://www.wolframalpha.com/examples/mathematics/numbers/base-conversions"
+}

exercises/practice/hexadecimal/Hexadecimal.roc

@@ -0,0 +1,5 @@
+module [parse]
+
+parse : Str -> Result U64 _
+parse = \string ->
+    crash "Please implement the 'parse' function"

exercises/practice/hexadecimal/hexadecimal-test.roc

@@ -0,0 +1,239 @@
+app [main] {
+    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.15.0/SlwdbJ-3GR7uBWQo6zlmYWNYOxnvo8r6YABXD-45UOw.tar.br",
+}
+
+main =
+    Task.ok {}
+
+import Hexadecimal exposing [parse]
+
+# Parse "0"
+expect
+    result = parse "0"
+    result == Ok 0
+
+# Parse "1"
+expect
+    result = parse "1"
+    result == Ok 1
+
+# Parse "2"
+expect
+    result = parse "2"
+    result == Ok 2
+
+# Parse "3"
+expect
+    result = parse "3"
+    result == Ok 3
+
+# Parse "4"
+expect
+    result = parse "4"
+    result == Ok 4
+
+# Parse "5"
+expect
+    result = parse "5"
+    result == Ok 5
+
+# Parse "6"
+expect
+    result = parse "6"
+    result == Ok 6
+
+# Parse "7"
+expect
+    result = parse "7"
+    result == Ok 7
+
+# Parse "8"
+expect
+    result = parse "8"
+    result == Ok 8
+
+# Parse "9"
+expect
+    result = parse "9"
+    result == Ok 9
+
+# Parse "a"
+expect
+    result = parse "a"
+    result == Ok 10
+
+# Parse "b"
+expect
+    result = parse "b"
+    result == Ok 11
+
+# Parse "c"
+expect
+    result = parse "c"
+    result == Ok 12
+
+# Parse "d"
+expect
+    result = parse "d"
+    result == Ok 13
+
+# Parse "e"
+expect
+    result = parse "e"
+    result == Ok 14
+
+# Parse "f"
+expect
+    result = parse "f"
+    result == Ok 15
+
+# Parse "10"
+expect
+    result = parse "10"
+    result == Ok 16
+
+# Parse "11"
+expect
+    result = parse "11"
+    result == Ok 17
+
+# Parse "1f"
+expect
+    result = parse "1f"
+    result == Ok 31
+
+# Parse "ff"
+expect
+    result = parse "ff"
+    result == Ok 255
+
+# Parse "abc"
+expect
+    result = parse "abc"
+    result == Ok 2748
+
+# Parse "cafe"
+expect
+    result = parse "cafe"
+    result == Ok 51966
+
+# Parse "deadbeef"
+expect
+    result = parse "deadbeef"
+    result == Ok 3735928559
+
+# Parse "123456789abcdef"
+expect
+    result = parse "123456789abcdef"
+    result == Ok 81985529216486895
+
+# Parse "ffffffffffffffff", the largest U64 value
+expect
+    result = parse "ffffffffffffffff"
+    result == Ok 18446744073709551615
+
+# Ignore leading zeros in "00000"
+expect
+    result = parse "00000"
+    result == Ok 0
+
+# Ignore leading zeros in "00001"
+expect
+    result = parse "00001"
+    result == Ok 1
+
+# Ignore leading zeros in "0000a"
+expect
+    result = parse "0000a"
+    result == Ok 10
+
+# Ignore leading zeros in "000010"
+expect
+    result = parse "000010"
+    result == Ok 16
+
+# Ignore leading zeros in "0000ff"
+expect
+    result = parse "0000ff"
+    result == Ok 255
+
+# Ignore leading zeros in "0000a0000"
+expect
+    result = parse "0000a0000"
+    result == Ok 655360
+
+# Ignore leading zeros even before the largest U64 value
+expect
+    result = parse "0000ffffffffffffffff"
+    result == Ok 18446744073709551615
+
+# Accept upper case
+expect
+    result = parse "ABCDEF"
+    result == Ok 11259375
+
+# Accept mixed case
+expect
+    result = parse "aAbBcCdDeEfF"
+    result == Ok 187723572702975
+
+# Empty strings are invalid
+expect
+    result = parse ""
+    result |> Result.isErr
+
+# A string with only spaces is invalid
+expect
+    result = parse "   "
+    result |> Result.isErr
+
+# Leading spaces are invalid
+expect
+    result = parse " 12ab"
+    result |> Result.isErr
+
+# Trailing spaces are invalid
+expect
+    result = parse "12ab "
+    result |> Result.isErr
+
+# Spaces anywhere are invalid
+expect
+    result = parse "12 ab"
+    result |> Result.isErr
+
+# Invalid character in "1*2ab"
+expect
+    result = parse "1*2ab"
+    result |> Result.isErr
+
+# Invalid character in "12fg"
+expect
+    result = parse "12fg"
+    result |> Result.isErr
+
+# Invalid character in "12/ab"
+expect
+    result = parse "12/ab"
+    result |> Result.isErr
+
+# Invalid character in "12ab\n"
+expect
+    result = parse "12ab\n"
+    result |> Result.isErr
+
+# Invalid character in "12-ab"
+expect
+    result = parse "12-ab"
+    result |> Result.isErr
+
+# Invalid character in "12+ab"
+expect
+    result = parse "12+ab"
+    result |> Result.isErr
+
+# For numbers that don't fit in an U64, `parse` should return an error
+# instead of crashing
+expect
+    result = parse "100000000000000000000000000000000"
+    result |> Result.isErr