Add List Ops exercise (#596)

* [New Exercise]: List Ops

* Tidy up List Ops exercise
- Reduce difficulty (since most of the skeleton has been added)
- Move template helper methods to generator_plugin
- Add spacing between tests

* Fix exercise reference in List Ops skeleton

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": [
+    "kahgoh"
+  ],
+  "files": {
+    "solution": [
+      "src/list_ops.cr"
+    ],
+    "test": [
+      "spec/list_ops_spec.cr"
+    ],
+    "example": [
+      ".meta/src/example.cr"
+    ]
+  },
+  "blurb": "Implement basic list operations."
+}

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

@@ -0,0 +1,59 @@
+module ListOps(T)
+  def self.append(list1 : Array(T), list2 : Array(T)) : Array(T)
+    concat([list1, list2])
+  end
+
+  def self.concat(lists : Array(Array(T)))
+    result = [] of T
+    lists.each { |sublist|
+      sublist.each { |elem| result << elem }
+    }
+    result
+  end
+
+  def self.filter(list : Array(T), function : T -> Bool) : Array(T)
+    filtered = [] of T
+    list.each { |elem|
+      if function.call(elem)
+        filtered << elem
+      end
+    }
+    filtered
+  end
+
+  def self.length(list : Array(T)) : Int
+    count = 0
+    list.each { |_| count = count + 1 }
+    count
+  end
+
+  def self.map(list : Array(T), function : T -> _)
+    mapped = [] of T
+    list.each { |elem| mapped << function.call(elem) }
+    mapped
+  end
+
+  def self.foldl(list : Array(T), initial : _, function : _, T -> _)
+    acc = initial
+    list.each { |elem| acc = function.call(acc, elem) }
+    acc
+  end
+
+  def self.foldr(list : Array(T), initial : _, function : _, T -> _)
+    acc = initial
+    copy = list.clone
+    until copy.empty?
+      acc = function.call(acc, copy.pop)
+    end
+    acc
+  end
+
+  def self.reverse(list : Array(T)) : Array(T)
+    reversed = [] of T
+    copy = list.clone
+    until copy.empty?
+      reversed << copy.pop
+    end
+    reversed
+  end
+end

exercises/practice/list-ops/.meta/test_template.ecr

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+require "spec"
+require "../src/*"
+
+<%- 
+    # These are uuids of the test cases that use nested arrays.
+    tests_with_nested = ["d6ecd72c-197f-40c3-89a4-aa1f45827e09", "40872990-b5b8-4cb8-9085-d91fc0d05d26"]
+-%>
+describe "<%-= to_capitalized(@json["exercise"].to_s) %>" do
+    <%- @json["cases"].as_a.each do |describe| -%>
+        describe "<%= describe["description"].to_s %>" do
+            <%- describe["cases"].as_a.each do |cases| -%>
+                <%= status() %> "<%= cases["description"] %>" do
+                    <%- if cases["property"].to_s == "append" -%>
+                        ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list1"]) %>, <%= list_ops_array(cases["input"]["list2"]) %>).should eq(<%= list_ops_array(cases["expected"]) %>)
+                    <%- end -%>
+                    <%- if cases["property"].to_s == "concat" -%>
+                        ListOps.<%= cases["property"] %>(<%= list_ops_nestable(cases["input"]["lists"]) %>).should eq(<%= 
+                            if tests_with_nested.any?(cases["uuid"]) 
+                                list_ops_nestable(cases["expected"])
+                            else
+                                list_ops_array(cases["expected"]) 
+                            end%>)
+                    <%- end -%>
+                    <%- if cases["property"].to_s == "filter" -%>
+                        filter = <%= list_ops_function(cases["input"]["function"], ["Int32"]) %>
+                        ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list"]) %>, filter).should eq(<%= list_ops_array(cases["expected"]) %>)
+                    <%- end -%>
+                    <%- if cases["property"].to_s == "length" -%>
+                        ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list"]) %>).should eq(<%= cases["expected"] %>)
+                    <%- end -%>
+                    <%- if cases["property"].to_s == "map" -%>
+                        mapper = <%= list_ops_function(cases["input"]["function"], ["Int32"]) %>
+                        ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list"]) %>, mapper).should eq(<%= list_ops_array(cases["expected"]) %>)
+                    <%- end -%>
+                    <%- if ["foldl", "foldr"].any?(cases["property"]) -%>
+                        <%- # If the function performs a division, use Float64 -%>
+                        <%- if cases["input"]["function"].to_s.matches?(/.*->.*\/.*/) -%>
+                            folder = <%= list_ops_function(cases["input"]["function"], ["Float64", "Int32"]) %>
+                            ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list"]) %>, <%= cases["input"]["initial"] %>.to_f64, folder).should eq(<%= cases["expected"] %>.to_f64)                    
+                        <%- else -%>
+                            folder = <%= list_ops_function(cases["input"]["function"], ["Int32", "Int32"]) %>
+                            ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list"]) %>, <%= cases["input"]["initial"] %>, folder).should eq(<%= cases["expected"] %>)
+                        <%- end -%>
+                    <%- end -%>
+                    <%- if cases["property"].to_s == "reverse" -%>
+                        <%- if tests_with_nested.any?(cases["uuid"]) -%>
+                            ListOps.<%= cases["property"] %>(<%= list_ops_nestable(cases["input"]["list"]) %>).should eq(<%= list_ops_nestable(cases["expected"]) %>)
+                        <%- else -%>
+                            ListOps.<%= cases["property"] %>(<%= list_ops_array(cases["input"]["list"]) %>).should eq(<%= list_ops_array(cases["expected"]) %>)
+                        <%- end -%>
+                    <%- end -%>
+                end
+
+            <%- end -%>
+        end
+
+    <%- end -%>
+end

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/spec/list_ops_spec.cr

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+require "spec"
+require "../src/*"
+
+describe "ListOps" do
+  describe "append entries to a list and return the new list" do
+    it "empty lists" do
+      ListOps.append([] of Int32, [] of Int32).should eq([] of Int32)
+    end
+
+    pending "list to empty list" do
+      ListOps.append([] of Int32, [1, 2, 3, 4]).should eq([1, 2, 3, 4])
+    end
+
+    pending "empty list to list" do
+      ListOps.append([1, 2, 3, 4], [] of Int32).should eq([1, 2, 3, 4])
+    end
+
+    pending "non-empty lists" do
+      ListOps.append([1, 2], [2, 3, 4, 5]).should eq([1, 2, 2, 3, 4, 5])
+    end
+  end
+
+  describe "concatenate a list of lists" do
+    pending "empty list" do
+      ListOps.concat([] of Array(Int32)).should eq([] of Int32)
+    end
+
+    pending "list of lists" do
+      ListOps.concat([[1, 2], [3], [] of Int32, [4, 5, 6]]).should eq([1, 2, 3, 4, 5, 6])
+    end
+
+    pending "list of nested lists" do
+      ListOps.concat([[[1], [2]], [[3]], [[] of Int32], [[4, 5, 6]]]).should eq([[1], [2], [3], [] of Int32, [4, 5, 6]])
+    end
+  end
+
+  describe "filter list returning only values that satisfy the filter function" do
+    pending "empty list" do
+      filter = ->(x : Int32) { x % 2 == 1 }
+      ListOps.filter([] of Int32, filter).should eq([] of Int32)
+    end
+
+    pending "non-empty list" do
+      filter = ->(x : Int32) { x % 2 == 1 }
+      ListOps.filter([1, 2, 3, 5], filter).should eq([1, 3, 5])
+    end
+  end
+
+  describe "returns the length of a list" do
+    pending "empty list" do
+      ListOps.length([] of Int32).should eq(0)
+    end
+
+    pending "non-empty list" do
+      ListOps.length([1, 2, 3, 4]).should eq(4)
+    end
+  end
+
+  describe "return a list of elements whose values equal the list value transformed by the mapping function" do
+    pending "empty list" do
+      mapper = ->(x : Int32) { x + 1 }
+      ListOps.map([] of Int32, mapper).should eq([] of Int32)
+    end
+
+    pending "non-empty list" do
+      mapper = ->(x : Int32) { x + 1 }
+      ListOps.map([1, 3, 5, 7], mapper).should eq([2, 4, 6, 8])
+    end
+  end
+
+  describe "folds (reduces) the given list from the left with a function" do
+    pending "empty list" do
+      folder = ->(acc : Int32, el : Int32) { el * acc }
+      ListOps.foldl([] of Int32, 2, folder).should eq(2)
+    end
+
+    pending "direction independent function applied to non-empty list" do
+      folder = ->(acc : Int32, el : Int32) { el + acc }
+      ListOps.foldl([1, 2, 3, 4], 5, folder).should eq(15)
+    end
+
+    pending "direction dependent function applied to non-empty list" do
+      folder = ->(acc : Float64, el : Int32) { el / acc }
+      ListOps.foldl([1, 2, 3, 4], 24.to_f64, folder).should eq(64.to_f64)
+    end
+  end
+
+  describe "folds (reduces) the given list from the right with a function" do
+    pending "empty list" do
+      folder = ->(acc : Int32, el : Int32) { el * acc }
+      ListOps.foldr([] of Int32, 2, folder).should eq(2)
+    end
+
+    pending "direction independent function applied to non-empty list" do
+      folder = ->(acc : Int32, el : Int32) { el + acc }
+      ListOps.foldr([1, 2, 3, 4], 5, folder).should eq(15)
+    end
+
+    pending "direction dependent function applied to non-empty list" do
+      folder = ->(acc : Float64, el : Int32) { el / acc }
+      ListOps.foldr([1, 2, 3, 4], 24.to_f64, folder).should eq(9.to_f64)
+    end
+  end
+
+  describe "reverse the elements of the list" do
+    pending "empty list" do
+      ListOps.reverse([] of Int32).should eq([] of Int32)
+    end
+
+    pending "non-empty list" do
+      ListOps.reverse([1, 3, 5, 7]).should eq([7, 5, 3, 1])
+    end
+
+    pending "list of lists is not flattened" do
+      ListOps.reverse([[1, 2], [3], [] of Int32, [4, 5, 6]]).should eq([[4, 5, 6], [] of Int32, [3], [1, 2]])
+    end
+  end
+end