feat: add list-ops exercise

config.json

@@ -642,6 +642,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "list-ops",
+        "name": "List Ops",
+        "uuid": "b1418b5d-9c69-438a-8835-cf12d630c547",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
       }
     ]
   },

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

@@ -0,0 +1,19 @@
+# ignore
+
+## Dart-specific instructions
+
+The `append` method mutates the receiver.
+All other methods return a new List.
+
+We can't override builtin methods and properties:
+instead of `length`, implement `count`;
+instead of `map`, implement `myMap`.
+
+You will be adding [Extension methods][extension] to the List class.
+Try not to rely too much on the builtin methods and properties of List and Iterable,
+implement the functionality yourself as much as you can.
+
+You'll notice that the provided stub file uses [Generics][generics].
+
+[extension]: https://dart.dev/language/extension-methods
+[generics]: https://dart.dev/language/generics

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

@@ -0,0 +1,19 @@
+# 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

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "lib/list_ops.dart"
+    ],
+    "test": [
+      "test/list_ops_test.dart"
+    ],
+    "example": [
+      ".meta/lib/example.dart"
+    ]
+  },
+  "blurb": "Implement basic list operations."
+}

exercises/practice/list-ops/.meta/lib/example.dart

@@ -0,0 +1,61 @@
+extension ListOps on List {
+  void append<T>(List<T> other) {
+    for (var elem in other) {
+      this.add(elem);
+    }
+  }
+
+  List<T> concat<T>() {
+    var result = <T>[];
+    for (var sublist in this) {
+      result.addAll(sublist);
+    }
+    return result;
+  }
+
+  List<T> filter<T>(bool Function(T elem) predicate) {
+    var result = <T>[];
+    for (var elem in this) {
+      if (predicate(elem)) {
+        result.add(elem);
+      }
+    }
+    return result;
+  }
+
+  int count() {
+    return this.foldl(0, (len, _) => len + 1);
+  }
+
+  List<T> myMap<T>(T Function(T elem) fn) {
+    var result = <T>[];
+    for (var elem in this) {
+      result.add(fn(elem));
+    }
+    return result;
+  }
+
+  U foldl<T, U>(U initial, U Function(U acc, T elem) fn) {
+    var result = initial;
+    for (var elem in this) {
+      result = fn(result, elem);
+    }
+    return result;
+  }
+
+  U foldr<T, U>(U initial, U Function(T elem, U acc) fn) {
+    var result = initial;
+    for (var elem in this.reverse()) {
+      result = fn(elem, result);
+    }
+    return result;
+  }
+
+  List<T> reverse<T>() {
+    var result = <T>[];
+    for (var i = this.length - 1; i >= 0; i--) {
+      result.add(this[i]);
+    }
+    return result;
+  }
+}

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

@@ -0,0 +1,106 @@
+# 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/analysis_options.yaml

@@ -0,0 +1,18 @@
+analyzer:
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+  errors:
+    unused_element:        error
+    unused_import:         error
+    unused_local_variable: error
+    dead_code:             error
+
+linter:
+  rules:
+    # Error Rules
+    - avoid_relative_lib_imports
+    - avoid_types_as_parameter_names
+    - literal_only_boolean_expressions
+    - no_adjacent_strings_in_list
+    - valid_regexps

exercises/practice/list-ops/lib/list_ops.dart

@@ -0,0 +1,33 @@
+extension ListOps on List {
+  void append<T>(List<T> other) {
+    // Add your implemenation here.
+  }
+
+  List<T> concat<T>() {
+    // Add your implemenation here.
+  }
+
+  List<T> filter<T>(bool Function(T elem) predicate) {
+    // Add your implemenation here.
+  }
+
+  int count() {
+    // Add your implemenation here.
+  }
+
+  List<T> myMap<T>(T Function(T elem) fn) {
+    // Add your implemenation here.
+  }
+
+  U foldl<T, U>(U initial, U Function(U acc, T elem) fn) {
+    // Add your implemenation here.
+  }
+
+  U foldr<T, U>(U initial, U Function(T elem, U acc) fn) {
+    // Add your implemenation here.
+  }
+
+  List<T> reverse<T>() {
+    // Add your implemenation here.
+  }
+}

exercises/practice/list-ops/pubspec.yaml

@@ -0,0 +1,5 @@
+name: 'list_ops'
+environment:
+  sdk: '>=2.18.0 <3.0.0'
+dev_dependencies:
+  test: '<2.0.0'