Add nth-prime exercise (#136)

* Add nth-prime exercise
* Switch to a recursive implementation as suggested by Isaac

config.json

@@ -371,6 +371,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "nth-prime",
+        "name": "Nth Prime",
+        "uuid": "43dd9f02-130f-4947-8469-37229e819748",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "pangram",
         "name": "Pangram",

exercises/practice/nth-prime/.docs/instructions.md

@@ -0,0 +1,7 @@
+# Instructions
+
+Given a number n, determine what the nth prime is.
+
+By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
+
+If your language provides methods in the standard library to deal with prime numbers, pretend they don't exist and implement them yourself.

exercises/practice/nth-prime/.meta/Example.roc

@@ -0,0 +1,26 @@
+module [prime]
+
+prime : U64 -> Result U64 [NoPrime0]
+prime = \number ->
+    if number == 0 then
+        Err NoPrime0
+    else if number == 1 then
+        Ok 2
+    else if number == 2 then
+        Ok 3
+    else
+        help = \primes, index ->
+            if List.len primes == number then
+                primes
+            else
+                nextIndex = index + 2
+                newPrimes =
+                    if primes |> List.any \p -> nextIndex % p == 0 then
+                        primes
+                    else
+                        primes |> List.append nextIndex
+                help newPrimes nextIndex
+        help [2, 3, 5] 5
+        |> List.last
+        |> Result.mapErr \_ ->
+            crash "Unreachable: list cannot be empty"

exercises/practice/nth-prime/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "NthPrime.roc"
+    ],
+    "test": [
+      "nth-prime-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "blurb": "Given a number n, determine what the nth prime is.",
+  "source": "A variation on Problem 7 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=7"
+}

exercises/practice/nth-prime/.meta/template.j2

@@ -0,0 +1,17 @@
+{%- 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
+    result = {{ case["property"] | to_camel }} {{ case["input"]["number"] }}
+    {%- if case["expected"]["error"] %}
+    result |> Result.isErr
+    {%- else %}
+    result == Ok {{ case["expected"] }}
+    {%- endif %}
+
+{% endfor %}

exercises/practice/nth-prime/.meta/tests.toml

@@ -0,0 +1,25 @@
+# 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.
+
+[75c65189-8aef-471a-81de-0a90c728160c]
+description = "first prime"
+
+[2c38804c-295f-4701-b728-56dea34fd1a0]
+description = "second prime"
+
+[56692534-781e-4e8c-b1f9-3e82c1640259]
+description = "sixth prime"
+
+[fce1e979-0edb-412d-93aa-2c744e8f50ff]
+description = "big prime"
+
+[bd0a9eae-6df7-485b-a144-80e13c7d55b2]
+description = "there is no zeroth prime"

exercises/practice/nth-prime/NthPrime.roc

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

exercises/practice/nth-prime/nth-prime-test.roc

@@ -0,0 +1,37 @@
+# These tests are auto-generated with test data from:
+# https://github.com/exercism/problem-specifications/tree/main/exercises/nth-prime/canonical-data.json
+# File last updated on 2024-10-07
+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 NthPrime exposing [prime]
+
+# first prime
+expect
+    result = prime 1
+    result == Ok 2
+
+# second prime
+expect
+    result = prime 2
+    result == Ok 3
+
+# sixth prime
+expect
+    result = prime 6
+    result == Ok 13
+
+# big prime
+expect
+    result = prime 10001
+    result == Ok 104743
+
+# there is no zeroth prime
+expect
+    result = prime 0
+    result |> Result.isErr
+