feat: Add strain exercise (#175)

Author: keiravillekode

config.json

@@ -473,6 +473,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "strain",
+        "name": "Strain",
+        "uuid": "2da79b0f-d182-46c7-a4e4-f0246a0fad65",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "connect",
         "name": "Connect",

exercises/practice/strain/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Implement the `keep` and `discard` operation on collections.
+Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.
+
+For example, given the collection of numbers:
+
+- 1, 2, 3, 4, 5
+
+And the predicate:
+
+- is the number even?
+
+Then your keep operation should produce:
+
+- 2, 4
+
+While your discard operation should produce:
+
+- 1, 3, 5
+
+Note that the union of keep and discard is all the elements.
+
+The functions may be called `keep` and `discard`, or they may need different names in order to not clash with existing functions or concepts in your language.
+
+## Restrictions
+
+Keep your hands off that filter/reject/whatchamacallit functionality provided by your standard library!
+Solve this one yourself using other basic tools instead.

exercises/practice/strain/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "strain.v"
+    ],
+    "test": [
+      "run_test.v"
+    ],
+    "example": [
+      ".meta/example.v"
+    ]
+  },
+  "blurb": "Implement the `keep` and `discard` operation on collections. Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.",
+  "source": "Conversation with James Edward Gray II",
+  "source_url": "http://graysoftinc.com/"
+}

exercises/practice/strain/.meta/example.v

@@ -0,0 +1,25 @@
+module main
+
+pub fn keep[T](array []T, predicate fn (e T) bool) []T {
+	mut result := []T{cap: array.len}
+
+	for element in array {
+		if predicate(element) {
+			result << element
+		}
+	}
+
+	return result
+}
+
+pub fn discard[T](array []T, predicate fn (e T) bool) []T {
+	mut result := []T{cap: array.len}
+
+	for element in array {
+		if !predicate(element) {
+			result << element
+		}
+	}
+
+	return result
+}

exercises/practice/strain/.meta/tests.toml

@@ -0,0 +1,45 @@
+# This is an auto-generated file. Regular comments will be removed when this
+# file is regenerated. Regenerating will not touch any manually added keys,
+# so comments can be added in a "comment" key.
+
+[26af8c32-ba6a-4eb3-aa0a-ebd8f136e003]
+description = "keep on empty list returns empty list"
+
+[f535cb4d-e99b-472a-bd52-9fa0ffccf454]
+description = "keeps everything"
+
+[950b8e8e-f628-42a8-85e2-9b30f09cde38]
+description = "keeps nothing"
+
+[92694259-6e76-470c-af87-156bdf75018a]
+description = "keeps first and last"
+
+[938f7867-bfc7-449e-a21b-7b00cbb56994]
+description = "keeps neither first nor last"
+
+[8908e351-4437-4d2b-a0f7-770811e48816]
+description = "keeps strings"
+
+[2728036b-102a-4f1e-a3ef-eac6160d876a]
+description = "keeps lists"
+
+[ef16beb9-8d84-451a-996a-14e80607fce6]
+description = "discard on empty list returns empty list"
+
+[2f42f9bc-8e06-4afe-a222-051b5d8cd12a]
+description = "discards everything"
+
+[ca990fdd-08c2-4f95-aa50-e0f5e1d6802b]
+description = "discards nothing"
+
+[71595dae-d283-48ca-a52b-45fa96819d2f]
+description = "discards first and last"
+
+[ae141f79-f86d-4567-b407-919eaca0f3dd]
+description = "discards neither first nor last"
+
+[daf25b36-a59f-4f29-bcfe-302eb4e43609]
+description = "discards strings"
+
+[a38d03f9-95ad-4459-80d1-48e937e4acaf]
+description = "discards lists"

exercises/practice/strain/run_test.v

@@ -0,0 +1,148 @@
+module main
+
+const empty = []int{cap: 0}
+
+fn test_keep_on_empty_list_returns_empty_list() {
+	predicate := fn (x int) bool {
+		return true
+	}
+	assert keep(empty, predicate) == empty
+}
+
+fn test_keeps_everything() {
+	array := [1, 3, 5]
+	predicate := fn (x int) bool {
+		return true
+	}
+	expect := [1, 3, 5]
+	assert keep(array, predicate) == expect
+}
+
+fn test_keeps_nothing() {
+	array := [1, 3, 5]
+	predicate := fn (x int) bool {
+		return false
+	}
+	assert keep(array, predicate) == empty
+}
+
+fn test_keeps_first_and_last() {
+	array := [1, 2, 3]
+	predicate := fn (x int) bool {
+		return x % 2 == 1
+	}
+	expect := [1, 3]
+	assert keep(array, predicate) == expect
+}
+
+fn test_keeps_neither_first_nor_last() {
+	array := [1, 2, 3]
+	predicate := fn (x int) bool {
+		return x % 2 == 0
+	}
+	expect := [2]
+	assert keep(array, predicate) == expect
+}
+
+fn test_keeps_strings() {
+	array := ['apple', 'zebra', 'banana', 'zombies', 'cherimoya', 'zealot']
+	predicate := fn (x string) bool {
+		return x.starts_with('z')
+	}
+	expect := ['zebra', 'zombies', 'zealot']
+	assert keep(array, predicate) == expect
+}
+
+fn test_keeps_lists() {
+	array := [
+		[1, 2, 3],
+		[5, 5, 5],
+		[5, 1, 2],
+		[2, 1, 2],
+		[1, 5, 2],
+		[2, 2, 1],
+		[1, 2, 5],
+	]
+	predicate := fn (x []int) bool {
+		return x.contains(5)
+	}
+	expect := [
+		[5, 5, 5],
+		[5, 1, 2],
+		[1, 5, 2],
+		[1, 2, 5],
+	]
+	assert keep(array, predicate) == expect
+}
+
+fn test_discard_on_empty_list_returns_empty_list() {
+	predicate := fn (x int) bool {
+		return true
+	}
+	assert discard(empty, predicate) == empty
+}
+
+fn test_discards_everything() {
+	array := [1, 3, 5]
+	predicate := fn (x int) bool {
+		return true
+	}
+	assert discard(array, predicate) == empty
+}
+
+fn test_discards_nothing() {
+	array := [1, 3, 5]
+	predicate := fn (x int) bool {
+		return false
+	}
+	expect := [1, 3, 5]
+	assert discard(array, predicate) == expect
+}
+
+fn test_discards_first_and_last() {
+	array := [1, 2, 3]
+	predicate := fn (x int) bool {
+		return x % 2 == 1
+	}
+	expect := [2]
+	assert discard(array, predicate) == expect
+}
+
+fn test_discards_neither_first_nor_last() {
+	array := [1, 2, 3]
+	predicate := fn (x int) bool {
+		return x % 2 == 0
+	}
+	expect := [1, 3]
+	assert discard(array, predicate) == expect
+}
+
+fn test_discards_strings() {
+	array := ['apple', 'zebra', 'banana', 'zombies', 'cherimoya', 'zealot']
+	predicate := fn (x string) bool {
+		return x.starts_with('z')
+	}
+	expect := ['apple', 'banana', 'cherimoya']
+	assert discard(array, predicate) == expect
+}
+
+fn test_discards_lists() {
+	array := [
+		[1, 2, 3],
+		[5, 5, 5],
+		[5, 1, 2],
+		[2, 1, 2],
+		[1, 5, 2],
+		[2, 2, 1],
+		[1, 2, 5],
+	]
+	predicate := fn (x []int) bool {
+		return x.contains(5)
+	}
+	expect := [
+		[1, 2, 3],
+		[2, 1, 2],
+		[2, 2, 1],
+	]
+	assert discard(array, predicate) == expect
+}

exercises/practice/strain/strain.v

@@ -0,0 +1,7 @@
+module main
+
+pub fn keep[T](array []T, predicate fn (e T) bool) []T {
+}
+
+pub fn discard[T](array []T, predicate fn (e T) bool) []T {
+}