Add list-ops

config.json

@@ -510,6 +510,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "list-ops",
+        "name": "List Ops",
+        "uuid": "2f1a1b01-d8ae-46c7-a439-51923382d2cd",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
       }
     ]
   },

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": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "list-ops.coffee"
+    ],
+    "test": [
+      "list-ops.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "Implement basic list operations."
+}

exercises/practice/list-ops/.meta/example.coffee

@@ -0,0 +1,42 @@
+class ListOps
+  @append: (list1, list2) ->
+    @concat([list1, list2])
+
+  @concat: (lists) ->
+    results = []
+    for list in lists
+      for elt in list
+        results.push elt
+    results
+
+  @filter: (list, f) ->
+    (elt for elt in list when f(elt))
+
+  @mylength: (list) ->
+    fn = (acc, _) -> acc + 1
+    @foldl(list, fn, 0)
+
+  @map: (list, fn) ->
+    (fn(elt) for elt in list)
+
+  @foldl: (list, fn, initial) ->
+    results = initial
+    for elt in list
+      results = fn(results, elt)
+    results
+
+  @foldr: (list, fn, initial) ->
+    if list.length == 0
+      initial
+    else
+      last = list.pop()
+      @foldr(list, fn, fn(initial, last))
+
+  @reverse: (list) ->
+    if list.length == 0
+      list
+    else
+      start = list.length - 1
+      (list[i] for i in [start..0])
+
+module.exports = ListOps

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/list-ops.coffee

@@ -0,0 +1,18 @@
+class ListOps
+  @append: (list1, list2) ->
+
+  @concat: (lists) ->
+
+  @filter: (list, f) ->
+
+  @mylength: (list) ->
+
+  @map: (list, fn) ->
+
+  @foldl: (list, fn, initial) ->
+
+  @foldr: (list, fn, initial) ->
+
+  @reverse: (list) ->
+
+module.exports = ListOps

exercises/practice/list-ops/list-ops.spec.coffee

@@ -0,0 +1,132 @@
+ListOps = require './list-ops'
+
+describe "List Ops", ->
+    it "append empty lists", ->
+      list1 = []
+      list2 = []
+      result = ListOps.append list1, list2
+      expect(result).toEqual []
+
+    xit "append -> list to empty list", ->
+      list1 = []
+      list2 = [1, 2, 3, 4]
+      result = ListOps.append list1, list2
+      expect(result).toEqual [1, 2, 3, 4]
+
+    xit "append -> empty list to list", ->
+      list1 = [1, 2, 3, 4]
+      list2 = []
+      result = ListOps.append list1, list2
+      expect(result).toEqual [1, 2, 3, 4]
+
+    xit "append -> non-empty lists", ->
+      list1 = [1, 2]
+      list2 = [2, 3, 4, 5]
+      result = ListOps.append list1, list2
+      expect(result).toEqual [1, 2, 2, 3, 4, 5]
+
+    xit "concatenate -> empty list", ->
+      lists = []
+      result = ListOps.concat lists
+      expect(result).toEqual []
+
+    xit "concatenate -> list of lists", ->
+      lists = [[1, 2], [3], [], [4, 5, 6]]
+      result = ListOps.concat lists
+      expect(result).toEqual [1, 2, 3, 4, 5, 6]
+
+    xit "concatenate -> list of nested lists", ->
+      lists = [[[1], [2]], [[3]], [[]], [[4, 5, 6]]]
+      result = ListOps.concat lists
+      expect(result).toEqual [[1], [2], [3], [], [4, 5, 6]]
+
+    xit "filter -> empty list", ->
+      list = []
+      fn = (x) -> x % 2 == 1
+      result = ListOps.filter list, fn
+      expect(result).toEqual []
+
+    xit "filter -> non-empty list", ->
+      list = [1, 2, 3, 5]
+      fn = (x) -> x % 2 == 1
+      result = ListOps.filter list, fn
+      expect(result).toEqual [1, 3, 5]
+
+    xit "length -> empty list", ->
+      list = []
+      result = ListOps.mylength list
+      expect(result).toEqual 0
+
+    xit "length -> non-empty list", ->
+      list = [1, 2, 3, 4]
+      result = ListOps.mylength list
+      expect(result).toEqual 4
+
+    xit "map -> empty list", ->
+      list = []
+      fn = (x) -> x + 1
+      result = ListOps.map list, fn
+      expect(result).toEqual []
+
+    xit "map -> non-empty list", ->
+      list = [1, 3, 5, 7]
+      fn = (x) -> x + 1
+      result = ListOps.map list, fn
+      expect(result).toEqual [2, 4, 6, 8]
+
+    xit "fold left -> empty list", ->
+      list = []
+      initial = 2
+      fn = (acc, el) -> el * acc
+      result = ListOps.foldl list, fn, initial
+      expect(result).toEqual 2
+
+    xit "fold left -> direction independent function applied to non-empty list", ->
+      list = [1, 2, 3, 4]
+      initial = 5
+      fn = (acc, el) -> el + acc
+      result = ListOps.foldl list, fn, initial
+      expect(result).toEqual 15
+
+    xit "fold left -> direction dependent function applied to non-empty list", ->
+      list = [1, 2, 3, 4]
+      initial = 24
+      fn = (acc, el) -> el / acc
+      result = ListOps.foldl list, fn, initial
+      expect(result).toEqual 64
+
+    xit "fold right -> empty list", ->
+      list = []
+      initial = 2
+      fn = (acc, el) -> el * acc
+      result = ListOps.foldr list, fn, initial
+      expect(result).toEqual 2
+
+    xit "fold right -> direction independent function applied to non-empty list", ->
+      list = [1, 2, 3, 4]
+      initial = 5
+      fn = (acc, el) -> el + acc
+      result = ListOps.foldr list, fn, initial
+      expect(result).toEqual 15
+
+    xit "fold right -> direction dependent function applied to non-empty list", ->
+      list = [1, 2, 3, 4]
+      initial = 24
+      fn = (acc, el) -> el / acc
+      result = ListOps.foldr list, fn, initial
+      expect(result).toEqual 9
+
+    xit "reverse -> empty list", ->
+      list = []
+      result = ListOps.reverse list
+      expect(result).toEqual []
+
+    xit "reverse -> non-empty list", ->
+      list = [1, 3, 5, 7]
+      result = ListOps.reverse list
+      expect(result).toEqual [7, 5, 3, 1]
+
+    xit "reverse -> list of lists is not flattened", ->
+      list = [[1, 2], [3], [], [4, 5, 6]]
+      result = ListOps.reverse list
+      expect(result).toEqual [[4, 5, 6], [], [3], [1, 2]]