Add list-ops exercise

Co-authored-by: Bobby Towers <porkostomus@mail.com>

exercises/practice/list-ops/.docs/instructions.md

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+# Instructions
+
+Implement basic list operations.
+
+In functional languages list operations like `length`, `map`, and `reduce` are very common.
+Implement a series of basic list operations, without using existing functions.
+
+The precise number and names of the operations to be implemented will be track dependent to avoid conflicts with existing names, but the general operations you will implement include:
+
+- `append` (_given two lists, add all items in the second list to the end of the first list_);
+- `concatenate` (_given a series of lists, combine all items in all lists into one flattened list_);
+- `filter` (_given a predicate and a list, return the list of all items for which `predicate(item)` is True_);
+- `length` (_given a list, return the total number of items within it_);
+- `map` (_given a function and a list, return the list of the results of applying `function(item)` on all items_);
+- `foldl` (_given a function, a list, and initial accumulator, fold (reduce) each item into the accumulator from the left_);
+- `foldr` (_given a function, a list, and an initial accumulator, fold (reduce) each item into the accumulator from the right_);
+- `reverse` (_given a list, return a list with all the original items, but in reversed order_).
+
+Note, the ordering in which arguments are passed to the fold functions (`foldl`, `foldr`) is significant.

exercises/practice/list-ops/.meta/config.json

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+{
+  "authors": [
+    "bobbicodes"
+  ],
+  "contributors": [
+    "kahgoh"
+  ],
+  "files": {
+    "solution": [
+      "src/list_ops.clj"
+    ],
+    "test": [
+      "test/list_ops_test.clj"
+    ],
+    "example": [
+      "src/example.clj"
+    ]
+  },
+  "blurb": "Implement basic list operations."
+}

exercises/practice/list-ops/.meta/src/example.clj

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+(ns list-ops)
+
+(defn append [list1 list2] 
+  (list-ops/foldl (fn [acc elem] (conj acc elem)) list2 list1))
+
+(defn concat [list]
+  (cond
+    (empty? list) []
+    :else (list-ops/foldl (fn [acc elem] (list-ops/append acc elem)) (rest list) (first list))))
+
+(defn filter [f list]
+  (loop [acc [] l list]
+    (cond 
+      (empty? l) acc
+      (f (first l)) (recur (conj acc (first l)) (rest l))
+      :else (recur acc (rest l)))))
+
+(defn length [list]
+  (list-ops/foldl (fn [acc elem] (+ acc 1)) list 0))
+
+(defn map [f list]
+  (list-ops/foldl (fn [acc elem] (conj acc (f elem))) list []))
+(defn foldl [f list init]
+  (loop [acc init l list]
+    (cond
+      (empty? l) acc
+      :else (recur (f acc (first l)) (rest l)))))
+
+(defn foldr [f list init]
+  (list-ops/foldl f (list-ops/reverse list) init))
+
+(defn reverse [list]
+  (list-ops/foldl (fn [acc elem] (cons elem acc)) list []))

exercises/practice/list-ops/.meta/tests.toml

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+# 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.
+
+[485b9452-bf94-40f7-a3db-c3cf4850066a]
+description = "append entries to a list and return the new list -> empty lists"
+
+[2c894696-b609-4569-b149-8672134d340a]
+description = "append entries to a list and return the new list -> list to empty list"
+
+[e842efed-3bf6-4295-b371-4d67a4fdf19c]
+description = "append entries to a list and return the new list -> empty list to list"
+
+[71dcf5eb-73ae-4a0e-b744-a52ee387922f]
+description = "append entries to a list and return the new list -> non-empty lists"
+
+[28444355-201b-4af2-a2f6-5550227bde21]
+description = "concatenate a list of lists -> empty list"
+
+[331451c1-9573-42a1-9869-2d06e3b389a9]
+description = "concatenate a list of lists -> list of lists"
+
+[d6ecd72c-197f-40c3-89a4-aa1f45827e09]
+description = "concatenate a list of lists -> list of nested lists"
+
+[0524fba8-3e0f-4531-ad2b-f7a43da86a16]
+description = "filter list returning only values that satisfy the filter function -> empty list"
+
+[88494bd5-f520-4edb-8631-88e415b62d24]
+description = "filter list returning only values that satisfy the filter function -> non-empty list"
+
+[1cf0b92d-8d96-41d5-9c21-7b3c37cb6aad]
+description = "returns the length of a list -> empty list"
+
+[d7b8d2d9-2d16-44c4-9a19-6e5f237cb71e]
+description = "returns the length of a list -> non-empty list"
+
+[c0bc8962-30e2-4bec-9ae4-668b8ecd75aa]
+description = "return a list of elements whose values equal the list value transformed by the mapping function -> empty list"
+
+[11e71a95-e78b-4909-b8e4-60cdcaec0e91]
+description = "return a list of elements whose values equal the list value transformed by the mapping function -> non-empty list"
+
+[613b20b7-1873-4070-a3a6-70ae5f50d7cc]
+description = "folds (reduces) the given list from the left with a function -> empty list"
+include = false
+
+[e56df3eb-9405-416a-b13a-aabb4c3b5194]
+description = "folds (reduces) the given list from the left with a function -> direction independent function applied to non-empty list"
+include = false
+
+[d2cf5644-aee1-4dfc-9b88-06896676fe27]
+description = "folds (reduces) the given list from the left with a function -> direction dependent function applied to non-empty list"
+include = false
+
+[36549237-f765-4a4c-bfd9-5d3a8f7b07d2]
+description = "folds (reduces) the given list from the left with a function -> empty list"
+reimplements = "613b20b7-1873-4070-a3a6-70ae5f50d7cc"
+
+[7a626a3c-03ec-42bc-9840-53f280e13067]
+description = "folds (reduces) the given list from the left with a function -> direction independent function applied to non-empty list"
+reimplements = "e56df3eb-9405-416a-b13a-aabb4c3b5194"
+
+[d7fcad99-e88e-40e1-a539-4c519681f390]
+description = "folds (reduces) the given list from the left with a function -> direction dependent function applied to non-empty list"
+reimplements = "d2cf5644-aee1-4dfc-9b88-06896676fe27"
+
+[aeb576b9-118e-4a57-a451-db49fac20fdc]
+description = "folds (reduces) the given list from the right with a function -> empty list"
+include = false
+
+[c4b64e58-313e-4c47-9c68-7764964efb8e]
+description = "folds (reduces) the given list from the right with a function -> direction independent function applied to non-empty list"
+include = false
+
+[be396a53-c074-4db3-8dd6-f7ed003cce7c]
+description = "folds (reduces) the given list from the right with a function -> direction dependent function applied to non-empty list"
+include = false
+
+[17214edb-20ba-42fc-bda8-000a5ab525b0]
+description = "folds (reduces) the given list from the right with a function -> empty list"
+reimplements = "aeb576b9-118e-4a57-a451-db49fac20fdc"
+
+[e1c64db7-9253-4a3d-a7c4-5273b9e2a1bd]
+description = "folds (reduces) the given list from the right with a function -> direction independent function applied to non-empty list"
+reimplements = "c4b64e58-313e-4c47-9c68-7764964efb8e"
+
+[8066003b-f2ff-437e-9103-66e6df474844]
+description = "folds (reduces) the given list from the right with a function -> direction dependent function applied to non-empty list"
+reimplements = "be396a53-c074-4db3-8dd6-f7ed003cce7c"
+
+[94231515-050e-4841-943d-d4488ab4ee30]
+description = "reverse the elements of the list -> empty list"
+
+[fcc03d1e-42e0-4712-b689-d54ad761f360]
+description = "reverse the elements of the list -> non-empty list"
+
+[40872990-b5b8-4cb8-9085-d91fc0d05d26]
+description = "reverse the elements of the list -> list of lists is not flattened"

exercises/practice/list-ops/deps.edn

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+{:aliases {:test {:extra-paths ["test"]
+                 :extra-deps {io.github.cognitect-labs/test-runner 
+                              {:git/url "https://github.com/cognitect-labs/test-runner.git"
+                               :sha "705ad25bbf0228b1c38d0244a36001c2987d7337"}}
+                 :main-opts ["-m" "cognitect.test-runner"]
+                 :exec-fn cognitect.test-runner.api/test}}}

exercises/practice/list-ops/project.clj

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+(defproject list-ops "0.1.0-SNAPSHOT"
+  :description "list-ops exercise."
+  :url "https://github.com/exercism/clojure/tree/main/exercises/list-ops"
+  :dependencies [[org.clojure/clojure "1.10.0"]])

exercises/practice/list-ops/src/list_ops.clj

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+(ns list-ops)
+
+(defn append [list1 list2] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn concat [list] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn filter [f list] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn length [list] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn map [f list] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn foldl [f list init] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn foldr [f list init] ;; <- arglist goes here
+  ;; your code goes here
+)
+
+(defn reverse [list] ;; <- arglist goes here
+  ;; your code goes here
+)

exercises/practice/list-ops/test/list_ops_test.clj

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+(ns list-ops-test
+  (:require [clojure.test :refer [deftest testing is]]
+             list-ops))
+
+(deftest append-test
+  (testing "empty lists"
+     (is (= [] (list-ops/append [] []))))
+  (testing "list to empty list"
+     (is (= [1 2 3 4] (list-ops/append [] [1 2 3 4]))))
+  (testing "empty list to list"
+     (is (= [1 2 3 4] (list-ops/append [1 2 3 4] []))))
+  (testing "non-empty lists"
+     (is (= [1 2 2 3 4 5] (list-ops/append [1 2] [2 3 4 5])))))
+
+(deftest concat-test
+  (testing "empty list"
+     (is (= [] (list-ops/concat []))))
+  (testing "list of lists"
+     (is (= [1 2 3 4 5 6] (list-ops/concat [[1 2] [3] [] [4 5 6]]))))
+  (testing "list of nested lists"
+     (is (= [[1] [2] [3] [] [4 5 6]] (list-ops/concat [[[1] [2]] [[3]] [[]] [[4 5 6]]])))))
+
+(deftest filter-test
+  (testing "empty list"
+     (is (= [] (list-ops/filter (fn [x] (= (mod x 2) 1)) [])))
+  (testing "non-empty list"
+     (is (= [1 3 5] (list-ops/filter (fn [x] (= (mod x 2) 1)) [1 2 3 5]))))))
+
+(deftest length-test
+  (testing "empty list"
+     (is (= 0 (list-ops/length []))))
+  (testing "non-empty list"
+     (is (= 4 (list-ops/length [1 2 3 4])))))
+
+(deftest map-test
+  (testing "empty list"
+     (is (= [] (list-ops/map (fn [x] (+ x 1)) []))))
+  (testing "non-empty list"
+     (is (= [2 4 6 8] (list-ops/map (fn [x] (+ x 1)) [1 3 5 7])))))
+
+(deftest foldl-test
+  (testing "empty list"
+     (is (= 2 (list-ops/foldl (fn [acc el] (* el acc)) [] 2))))
+  (testing "direction independent function applied to non-empty list"
+     (is (= 15 (list-ops/foldl (fn [acc el] (+ el acc)) [1 2 3 4] 5))))
+  (testing "direction dependent function applied to non-empty list"
+     (is (= 64 (list-ops/foldl (fn [acc el] (/ el acc)) [1 2 3 4] 24)))))
+
+(deftest foldr-test
+  (testing "empty list"
+     (is (= 2 (list-ops/foldr (fn [acc el] (* el acc)) [] 2))))
+  (testing "direction independent function applied to non-empty list"
+     (is (= 15 (list-ops/foldr (fn [acc el] (+ el acc)) [1 2 3 4] 5))))
+  (testing "direction dependent function applied to non-empty list"
+     (is (= 9 (list-ops/foldr (fn [acc el] (/ el acc)) [1 2 3 4] 24)))))
+
+(deftest reverse-test
+  (testing "empty list"
+     (is (= [] (list-ops/reverse []))))
+  (testing "non-empty list"
+     (is (= [7 5 3 1] (list-ops/reverse [1 3 5 7]))))
+  (testing "list of lists is not flattened"
+     (is (= [[4 5 6] [] [3] [1 2]] (list-ops/reverse [[1 2] [3] [] [4 5 6]])))))
+
+;(clojure.test/run-tests)