Add list-ops exercise (#196)

config.json

@@ -43,9 +43,7 @@
         "uuid": "05345431-e18b-4737-9b40-dbca5fbb549c",
         "practices": [],
         "prerequisites": [],
-        "difficulty": 1,
-        "topics": [
-        ]
+        "difficulty": 1
       },
       {
         "slug": "accumulate",
@@ -61,8 +59,7 @@
         "name": "Acronym",
         "uuid": "d3b82743-950f-4577-ab3a-655ff3522c6b",
         "practices": [],
-        "prerequisites": [
-        ],
+        "prerequisites": [],
         "difficulty": 2
       },
       {
@@ -375,6 +372,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "list-ops",
+        "name": "List Ops",
+        "uuid": "f5ade076-6afd-4f03-8916-543cb7f350a1",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 1
       }
     ]
   },

exercises/practice/acronym/.meta/config.json

@@ -2,8 +2,6 @@
   "authors": [
     "kephas"
   ],
-  "contributors": [
-  ],
   "files": {
     "solution": [
       "src/acronym.lfe"

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.lfe"
+    ],
+    "test": [
+      "test/list-ops-tests.lfe"
+    ],
+    "example": [
+      ".meta/example.lfe"
+    ]
+  },
+  "blurb": "Implement basic list operations."
+}

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

@@ -0,0 +1,61 @@
+(defmodule list-ops
+  (export 
+    (append 2) 
+    (concat 1) 
+    (filter 2)
+    (length 1)
+    (map 2)
+    (foldl 3)
+    (foldr 3)
+    (reverse 1)
+  )
+)
+
+(defun append (list1 list2) (append-loop (reverse list1) list2))
+(defun append-loop
+  ((list1 []) (reverse list1))
+  ((list1 (cons next tail)) (append-loop (cons next list1) tail)))
+
+(defun concat (content) (concat-loop content '()))
+(defun concat-loop 
+  (('() acc) acc)
+  (((cons next tail) acc) (concat-loop tail (append acc next))))
+
+(defun filter (content filter-func)
+  (filter content '() filter-func)
+)
+
+(defun filter 
+  (('() acc filter-func) (lists:reverse acc))
+  (((cons next tail) acc filter-func)
+    (if (funcall filter-func next)
+      (filter tail (cons next acc) filter-func)
+      (filter tail acc filter-func)
+    )
+  )
+)
+
+(defun length (contents) (foldl-loop contents 0 (lambda (acc item) (+ acc 1))))
+
+(defun map (contents map-func)
+  (map-loop contents '() map-func)
+)
+(defun map-loop 
+  (('() acc map-func) (reverse acc))
+  (((cons next tail) acc map-func) (map-loop tail (cons (funcall map-func next) acc) map-func))
+)
+
+(defun foldl (contents initial fold-func) (foldl-loop contents initial fold-func))
+
+(defun foldr (contents initial fold-func) (foldl-loop (reverse contents) initial fold-func))
+
+(defun foldl-loop 
+  (('() acc fold-func) acc)
+  (((cons head tail) acc fold-func) (foldl-loop tail (funcall fold-func acc head) fold-func))
+)
+
+(defun reverse (contents) (reverse-loop contents '()))
+(defun reverse-loop
+  (('() reversed) reversed)
+  (((cons next tail) acc) (reverse-loop tail (cons next acc)))
+)

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/Makefile

@@ -0,0 +1,21 @@
+ERL    := $(shell which erl)
+REBAR3 := $(shell which rebar3)
+
+null  :=
+space := $(null) #
+comma := ,
+
+ifeq ($(ERL),)
+  $(error Can't find Erlang executable 'erl')
+else ifeq ($(REBAR3),)
+  $(error Can't find rebar3)
+endif
+
+compile: ; $(REBAR3) compile
+
+clean: ; $(REBAR3) clean
+
+.PHONY: test
+test:
+	$(REBAR3) eunit \
+	-m $(subst $(space),$(comma),$(basename $(notdir $(wildcard test/*.lfe))))

exercises/practice/list-ops/rebar.config

@@ -0,0 +1,11 @@
+{plugins, [{rebar3_lfe, "0.4.3"}]}.
+
+{provider_hooks, [{post, [{compile, {lfe, compile}}]}]}.
+
+{deps, [{lfe, "2.1.1"}]}.
+
+{profiles,
+ [{test,
+   [{eunit_compile_opts, [{src_dirs, ["src", "test"]}]},
+    {deps,
+     [{ltest, "0.13.3"}]}]}]}.

exercises/practice/list-ops/rebar.lock

@@ -0,0 +1,8 @@
+{"1.2.0",
+[{<<"lfe">>,{pkg,<<"lfe">>,<<"2.1.1">>},0}]}.
+[
+{pkg_hash,[
+ {<<"lfe">>, <<"4A888B26172D198DC7A5AFEB897E8248AF7D56E1638D9C8249AAF933AE811B96">>}]},
+{pkg_hash_ext,[
+ {<<"lfe">>, <<"C484D3B655D40DED58BC41B17B22F173711C681BF36063A234A9BAA9506947E1">>}]}
+].

exercises/practice/list-ops/src/list-ops.app.src

@@ -0,0 +1,10 @@
+%% -*- erlang -*-
+{application, 'list-ops',
+ [{description, "Implement basic list operations."},
+  {vsn, "0.0.1"},
+  {modules,['list-ops']},
+  {registered, []},
+  {applications,
+   [kernel, stdlib]},
+  {included_applications, []},
+  {env, []}]}.

exercises/practice/list-ops/src/list-ops.lfe

@@ -0,0 +1,44 @@
+(defmodule list-ops
+  (export 
+    (append 2) 
+    (concat 1) 
+    (filter 2)
+    (length 1)
+    (map 2)
+    (foldl 3)
+    (foldr 3)
+    (reverse 1)
+  )
+)
+
+(defun append (list1 list2) 
+  ; Please implement the 'append' function
+)
+
+(defun concat (content) 
+  ; Please implement the 'concat' function
+)
+
+(defun filter (content filter-func)
+  ; Please implement the 'filter' function
+)
+
+(defun length (contents) 
+  ; Please implement the 'length' function
+)
+
+(defun map (contents map-func)
+  ; Please implement the 'map' function
+)
+
+(defun foldl (contents initial fold-func) 
+  ; Please implement the 'foldl' function
+)
+
+(defun foldr (contents initial fold-func) 
+  ; Please implement the 'foldr' function
+)
+
+(defun reverse (contents)
+  ; Please implement the 'reverse' function
+)