Publish list-ops (#685)

* remove wip status * add vectors as prerequisite * make instructions append more clear * change 'init' parameter to 'acc' * split into one deftest per test * update instructions append * rewrite example solution * update starter file * update instructions append * add implementation for the optional goal (lists)
exercism · Nov 12, 2024 · d94f4b5 · d94f4b5
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diff --git a/config.json b/config.json
@@ -1375,10 +1375,10 @@
         "practices": [],
         "prerequisites": [
           "lists",
-          "closures"
+          "closures",
+          "vectors"
         ],
-        "difficulty": 5,
-        "status": "wip"
+        "difficulty": 5
       }
     ]
   },

diff --git a/exercises/practice/list-ops/.docs/instructions.append.md b/exercises/practice/list-ops/.docs/instructions.append.md
@@ -1,8 +1,19 @@
 # Instructions append
 
-## Implementation tips
+## Appendix
 
-- The instructions use lists because they are synced with a shared repository to maintain consistency across tracks.
-  However, for this exercise in the Clojure track, you should assume that you are working with vectors instead of lists.
-- It is important not to reuse existing Clojure built-in functions with similar functionality, as doing so would diminish the intended learning value of the exercise.
-  Some of these functions include `into`, `concat`, `cat`, `lazy-cat`, `mapcat`, `flatten`, `filter`, `filterv`, `remove`, `count`, `map`, `mapv`, `reduce`, `transduce`, `reverse`, and `rseq` from the **clojure.core** namespace.
+The instructions are synced with a shared repository to ensure consistency across all language tracks.
+For this exercise in the Clojure track, assume both the input and output are vectors.
+As a stretch goal, consider how you could implement the solution without using lists anywhere in your code.
+Also, think about the efficiency of your program.
+
+It is important not to reuse existing Clojure built-in functions with similar functionality, as doing so would diminish the intended learning value of the exercise.
+Key functions from the **clojure.core** namespace to avoid include `into`, `concat`, `cat`, `lazy-cat`, `mapcat`, `flatten`, `filter`, `filterv`, `remove`, `count`, `map`, `mapv`, `reduce`, `transduce`, `reverse`, and `rseq`.
+
+### Optional goals
+
+Try to pass the tests by devising a solution that assumes both the input and output are lists instead of vectors.
+The test suite does not need to be modified.
+This time, consider how you could implement the solution without using vectors anywhere in your code.
+
+If you decide to publish this solution, be sure to include a comment indicating that it addresses the optional goal of using lists. Don't forget to update the docstrings!
diff --git a/exercises/practice/list-ops/.meta/config.json b/exercises/practice/list-ops/.meta/config.json
@@ -1,10 +1,10 @@
 {
   "authors": [
-    "bobbicodes"
+    "bobbicodes",
+    "tasxatzial"
   ],
   "contributors": [
-    "kahgoh",
-    "tasxatzial"
+    "kahgoh"
   ],
   "files": {
     "solution": [

diff --git a/exercises/practice/list-ops/.meta/src/example.clj b/exercises/practice/list-ops/.meta/src/example.clj
@@ -1,34 +1,50 @@
 (ns list-ops)
 
-(defn foldl [f coll init]
-  (loop [acc init l coll]
-    (cond
-      (empty? l) acc
-      :else (recur (f acc (first l)) (rest l)))))
-
-(defn append [coll1 coll2]
-  (list-ops/foldl (fn [acc elem] (conj acc elem)) coll2 coll1))
-
-(defn concatenate [coll]
-  (cond
-    (empty? coll) []
-    :else (list-ops/foldl (fn [acc elem] (list-ops/append acc elem)) (rest coll) (first coll))))
-
-(defn select-if [pred coll]
-  (loop [acc [] l coll]
-    (cond
-      (empty? l) acc
-      (pred (first l)) (recur (conj acc (first l)) (rest l))
-      :else (recur acc (rest l)))))
-
-(defn length [coll]
-  (list-ops/foldl (fn [acc elem] (+ acc 1)) coll 0))
-
-(defn apply-to-each [f coll]
-  (list-ops/foldl (fn [acc elem] (conj acc (f elem))) coll []))
-
-(defn reverse-order [coll]
-  (list-ops/foldl (fn [acc elem] (cons elem acc)) coll []))
-
-(defn foldr [f coll init]
-  (list-ops/foldl f (list-ops/reverse-order coll) init))
+(declare foldl)
+(declare reverse-order)
+
+(defn append
+  [coll1 coll2]
+  (foldl conj coll2 coll1))
+
+(defn concatenate
+  [colls]
+  (foldl append colls []))
+
+(defn select-if
+  [pred coll]
+  (let [reducer (fn [acc el]
+                  (if (pred el)
+                    (conj acc el)
+                    acc))]
+    (foldl reducer coll [])))
+
+(defn length
+  [coll]
+  (let [reducer (fn [acc _]
+                  (inc acc))]
+    (foldl reducer coll 0)))
+
+(defn apply-to-each
+  [f coll]
+  (let [reducer (fn [acc el]
+                  (conj acc (f el)))]
+    (foldl reducer coll [])))
+
+(defn foldl
+  [f coll acc]
+  (if (seq coll)
+    (recur f (rest coll) (f acc (first coll)))
+    acc))
+
+(defn foldr
+  [f coll acc]
+  (foldl f (reverse-order coll) acc))
+
+(defn reverse-order
+  [coll]
+  (loop [index (dec (length coll))
+         result []]
+    (if (neg? index)
+      result
+      (recur (dec index) (conj result (coll index))))))
diff --git a/exercises/practice/list-ops/.meta/src/example_lists.clj b/exercises/practice/list-ops/.meta/src/example_lists.clj
@@ -0,0 +1,46 @@
+(ns list-ops)
+
+(declare foldl)
+(declare reverse-order)
+
+(defn append
+  [coll1 coll2]
+  (reverse-order (foldl conj coll2 (reverse-order coll1))))
+
+(defn concatenate
+  [colls]
+  (foldl append colls ()))
+
+(defn select-if
+  [pred coll]
+  (let [reducer (fn [acc el]
+                  (if (pred el)
+                    (conj acc el)
+                    acc))]
+    (reverse-order (foldl reducer coll ()))))
+
+(defn length
+  [coll]
+  (let [reducer (fn [acc _]
+                  (inc acc))]
+    (foldl reducer coll 0)))
+
+(defn apply-to-each
+  [f coll]
+  (let [reducer (fn [acc el]
+                  (conj acc (f el)))]
+    (reverse-order (foldl reducer coll ()))))
+
+(defn foldl
+  [f coll acc]
+  (if (seq coll)
+    (recur f (rest coll) (f acc (first coll)))
+    acc))
+
+(defn foldr
+  [f coll acc]
+  (foldl f (reverse-order coll) acc))
+
+(defn reverse-order
+  [coll]
+  (foldl conj coll ()))
diff --git a/exercises/practice/list-ops/src/list_ops.clj b/exercises/practice/list-ops/src/list_ops.clj
@@ -3,47 +3,47 @@
 (defn append 
   "Given two vectors, it adds all the items in the second vector to the end of the first vector"
   [coll1 coll2]
-  ;; your code goes here
-)
+  ;; function body
+  )
 
 (defn concatenate 
   "Given a vector of vectors, it combines all the vectors into one flattened vector"
   [colls]
-  ;; your code goes here
-)
+  ;; function body
+  )
 
 (defn select-if
   "Given a predicate and a vector, it returns the vector of all items for which predicate(item) is true"
   [pred coll]
-  ;; your code goes here
-)
+  ;; function body
+  )
 
 (defn length 
   "Given a vector, it returns the number of items within it"
   [coll]
-  ;; your code goes here
-)
+  ;; function body
+  )
 
 (defn apply-to-each 
   "Given a function and a vector, it returns the vector of the results of applying function(item) on all items"
   [f coll]
-  ;; your code goes here
-)
+  ;; function body
+  )
 
 (defn foldl 
   "Given a function, a vector, and initial accumulator, it folds (reduces) each item into the accumulator from the left"
-  [f coll init]
-  ;; your code goes here
-)
+  [f coll acc]
+  ;; function body
+  )
 
 (defn foldr
   "Given a function, a vector, and an initial accumulator, it folds (reduces) each item into the accumulator from the right"
-  [f coll init]
-  ;; your code goes here
-)
+  [f coll acc]
+  ;; function body
+  )
 
 (defn reverse-order 
   "Given a vector, it returns a vector with all the original items, but in reverse order"
   [coll]
-  ;; your code goes here
-)
+  ;; function body
+  )
diff --git a/exercises/practice/list-ops/test/list_ops_test.clj b/exercises/practice/list-ops/test/list_ops_test.clj
@@ -2,62 +2,90 @@
   (:require [clojure.test :refer [deftest testing is]]
              list-ops))
 
-(deftest append-test
-  (testing "empty vectors"
-     (is (= [] (list-ops/append [] []))))
-  (testing "vector to empty vector"
-     (is (= [1 2 3 4] (list-ops/append [] [1 2 3 4]))))
-  (testing "empty vector to vector"
-     (is (= [1 2 3 4] (list-ops/append [1 2 3 4] []))))
-  (testing "non-empty vectors"
-     (is (= [1 2 2 3 4 5] (list-ops/append [1 2] [2 3 4 5])))))
-
-(deftest concatenate-test
-  (testing "empty vector"
-     (is (= [] (list-ops/concatenate []))))
-  (testing "vector of vectors"
-     (is (= [1 2 3 4 5 6] (list-ops/concatenate [[1 2] [3] [] [4 5 6]]))))
-  (testing "vector of nested vectors"
-     (is (= [[1] [2] [3] [] [4 5 6]] (list-ops/concatenate [[[1] [2]] [[3]] [[]] [[4 5 6]]])))))
-
-(deftest select-if-test
-  (testing "empty vector"
-     (is (= [] (list-ops/select-if (fn [x] (= (mod x 2) 1)) [])))
-  (testing "non-empty vector"
-     (is (= [1 3 5] (list-ops/select-if (fn [x] (= (mod x 2) 1)) [1 2 3 5]))))))
-
-(deftest length-test
-  (testing "empty vector"
-     (is (= 0 (list-ops/length []))))
-  (testing "non-empty vector"
-     (is (= 4 (list-ops/length [1 2 3 4])))))
-
-(deftest apply-to-each-test
-  (testing "empty vector"
-     (is (= [] (list-ops/apply-to-each (fn [x] (+ x 1)) []))))
-  (testing "non-empty vector"
-     (is (= [2 4 6 8] (list-ops/apply-to-each (fn [x] (+ x 1)) [1 3 5 7])))))
-
-(deftest foldl-test
-  (testing "empty vector"
-     (is (= 2 (list-ops/foldl (fn [acc el] (* el acc)) [] 2))))
-  (testing "direction independent function applied to non-empty vector"
-     (is (= 15 (list-ops/foldl (fn [acc el] (+ el acc)) [1 2 3 4] 5))))
-  (testing "direction dependent function applied to non-empty vector"
-     (is (= 64 (list-ops/foldl (fn [acc el] (/ el acc)) [1 2 3 4] 24)))))
-
-(deftest foldr-test
-  (testing "empty vector"
-     (is (= 2 (list-ops/foldr (fn [acc el] (* el acc)) [] 2))))
-  (testing "direction independent function applied to non-empty vector"
-     (is (= 15 (list-ops/foldr (fn [acc el] (+ el acc)) [1 2 3 4] 5))))
-  (testing "direction dependent function applied to non-empty vector"
-     (is (= 9 (list-ops/foldr (fn [acc el] (/ el acc)) [1 2 3 4] 24)))))
-
-(deftest reverse-order-test
-  (testing "empty vector"
-     (is (= [] (list-ops/reverse-order []))))
-  (testing "non-empty vector"
-     (is (= [7 5 3 1] (list-ops/reverse-order [1 3 5 7]))))
-  (testing "vector of vectors is not flattened"
-     (is (= [[4 5 6] [] [3] [1 2]] (list-ops/reverse-order [[1 2] [3] [] [4 5 6]])))))
+(deftest test-485b9452-bf94-40f7-a3db-c3cf4850066a
+  (testing "append entries to a vector and return the new vector -> empty vectors"
+    (is (= [] (list-ops/append [] [])))))
+
+(deftest test-2c894696-b609-4569-b149-8672134d340a
+  (testing "append entries to a vector and return the new vector -> vector to empty vector"
+    (is (= [1 2 3 4] (list-ops/append [] [1 2 3 4])))))
+
+(deftest test-e842efed-3bf6-4295-b371-4d67a4fdf19c
+  (testing "append entries to a vector and return the new vector -> empty vector to vector"
+    (is (= [1 2 3 4] (list-ops/append [1 2 3 4] [])))))
+
+(deftest test-71dcf5eb-73ae-4a0e-b744-a52ee387922f
+  (testing "append entries to a vector and return the new vector -> non-empty vectors"
+    (is (= [1 2 2 3 4 5] (list-ops/append [1 2] [2 3 4 5])))))
+
+(deftest test-28444355-201b-4af2-a2f6-5550227bde21
+  (testing "concatenate a vector of vectors -> empty vector"
+    (is (= [] (list-ops/concatenate [])))))
+
+(deftest test-331451c1-9573-42a1-9869-2d06e3b389a9
+  (testing "concatenate a vector of vectors -> vector of vectors"
+    (is (= [1 2 3 4 5 6] (list-ops/concatenate [[1 2] [3] [] [4 5 6]])))))
+
+(deftest test-d6ecd72c-197f-40c3-89a4-aa1f45827e09
+  (testing "concatenate a vector of vectors -> vector of nested vectors"
+    (is (= [[1] [2] [3] [] [4 5 6]] (list-ops/concatenate [[[1] [2]] [[3]] [[]] [[4 5 6]]])))))
+
+(deftest test-0524fba8-3e0f-4531-ad2b-f7a43da86a16
+  (testing "filter vector returning only values that satisfy the filter function -> empty vector"
+    (is (= [] (list-ops/select-if (fn [x] (= (mod x 2) 1)) [])))))
+
+(deftest test-88494bd5-f520-4edb-8631-88e415b62d24
+  (testing "filter vector returning only values that satisfy the filter function -> non-empty vector"
+    (is (= [1 3 5] (list-ops/select-if (fn [x] (= (mod x 2) 1)) [1 2 3 5])))))
+
+(deftest test-1cf0b92d-8d96-41d5-9c21-7b3c37cb6aad
+  (testing "returns the length of a vector -> empty vector"
+    (is (= 0 (list-ops/length [])))))
+
+(deftest test-d7b8d2d9-2d16-44c4-9a19-6e5f237cb71e
+  (testing "returns the length of a vector -> non-empty vector"
+    (is (= 4 (list-ops/length [1 2 3 4])))))
+
+(deftest test-c0bc8962-30e2-4bec-9ae4-668b8ecd75aa
+  (testing "return a vector of elements whose values equal the vector value transformed by the mapping function -> empty vector"
+    (is (= [] (list-ops/apply-to-each (fn [x] (+ x 1)) [])))))
+
+(deftest test-11e71a95-e78b-4909-b8e4-60cdcaec0e91
+  (testing "return a vector of elements whose values equal the vector value transformed by the mapping function -> non-empty vector"
+    (is (= [2 4 6 8] (list-ops/apply-to-each (fn [x] (+ x 1)) [1 3 5 7])))))
+
+(deftest test-36549237-f765-4a4c-bfd9-5d3a8f7b07d2
+  (testing "folds (reduces) the given vector from the left with a function -> empty vector"
+    (is (= 2 (list-ops/foldl (fn [acc el] (* el acc)) [] 2)))))
+
+(deftest test-7a626a3c-03ec-42bc-9840-53f280e13067
+  (testing "folds (reduces) the given vector from the left with a function -> direction independent function applied to non-empty vector"
+    (is (= 15 (list-ops/foldl (fn [acc el] (+ el acc)) [1 2 3 4] 5)))))
+
+(deftest test-d7fcad99-e88e-40e1-a539-4c519681f390
+  (testing "folds (reduces) the given vector from the left with a function -> direction dependent function applied to non-empty vector"
+    (is (= 64 (list-ops/foldl (fn [acc el] (/ el acc)) [1 2 3 4] 24)))))
+
+(deftest test-17214edb-20ba-42fc-bda8-000a5ab525b0
+  (testing "folds (reduces) the given vector from the right with a function -> empty vector"
+    (is (= 2 (list-ops/foldr (fn [acc el] (* el acc)) [] 2)))))
+
+(deftest test-e1c64db7-9253-4a3d-a7c4-5273b9e2a1bd
+  (testing "folds (reduces) the given vector from the right with a function -> direction independent function applied to non-empty vector"
+    (is (= 15 (list-ops/foldr (fn [acc el] (+ el acc)) [1 2 3 4] 5)))))
+
+(deftest test-8066003b-f2ff-437e-9103-66e6df474844
+  (testing "folds (reduces) the given vector from the right with a function -> direction dependent function applied to non-empty vector"
+    (is (= 9 (list-ops/foldr (fn [acc el] (/ el acc)) [1 2 3 4] 24)))))
+
+(deftest test-94231515-050e-4841-943d-d4488ab4ee30
+  (testing "reverse the elements of the vector -> empty vector"
+    (is (= [] (list-ops/reverse-order [])))))
+
+(deftest test-fcc03d1e-42e0-4712-b689-d54ad761f360
+  (testing "reverse the elements of the vector -> non-empty vector"
+    (is (= [7 5 3 1] (list-ops/reverse-order [1 3 5 7])))))
+
+(deftest test-40872990-b5b8-4cb8-9085-d91fc0d05d26
+  (testing "reverse the elements of the vector -> vector of vectors is not flattened"
+    (is (= [[4 5 6] [] [3] [1 2]] (list-ops/reverse-order [[1 2] [3] [] [4 5 6]])))))