add strain (#96)

* add `strain`

* Update spec generator

Author: BNAndras

config.json

@@ -194,6 +194,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "strain",
+        "name": "Strain",
+        "uuid": "9fd2db0a-e806-451c-9bea-3d895dccd6f6",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "sum-of-multiples",
         "name": "Sum of Multiples",

exercises/practice/strain/.busted

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

exercises/practice/strain/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Implement the `keep` and `discard` operation on collections.
+Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.
+
+For example, given the collection of numbers:
+
+- 1, 2, 3, 4, 5
+
+And the predicate:
+
+- is the number even?
+
+Then your keep operation should produce:
+
+- 2, 4
+
+While your discard operation should produce:
+
+- 1, 3, 5
+
+Note that the union of keep and discard is all the elements.
+
+The functions may be called `keep` and `discard`, or they may need different names in order to not clash with existing functions or concepts in your language.
+
+## Restrictions
+
+Keep your hands off that filter/reject/whatchamacallit functionality provided by your standard library!
+Solve this one yourself using other basic tools instead.

exercises/practice/strain/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "strain.moon"
+    ],
+    "test": [
+      "strain_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "blurb": "Implement the `keep` and `discard` operation on collections.",
+  "source": "Conversation with James Edward Gray II",
+  "source_url": "http://graysoftinc.com/"
+}

exercises/practice/strain/.meta/example.moon

@@ -0,0 +1,7 @@
+{
+  keep: (list, predicate) ->
+    [item for item in *list when predicate(item)]
+
+  discard: (list, predicate) ->
+    [item for item in *list when not predicate(item)]
+}

exercises/practice/strain/.meta/spec_generator.moon

@@ -0,0 +1,62 @@
+format_predicate = (pred) ->
+  switch pred
+    when "fn(x) -> true"
+      "(_) -> true"
+    when "fn(x) -> false"
+      "(_) -> false"
+    when "fn(x) -> x % 2 == 1"
+      "(num) -> num % 2 == 1"
+    when "fn(x) -> x % 2 == 0"
+      "(num) -> num % 2 == 0"
+    when "fn(x) -> contains(x, 5)"
+      "(list) -> contains list, 5"
+    when "fn(x) -> starts_with(x, 'z')"
+      "(str) -> starts_with str, 'z'"
+    else
+      pred
+
+format_list = (list) ->
+  if #list == 0
+    "{}"
+  elseif type(list[1]) == 'string'
+    "{" .. table.concat([quote(elem) for elem in *list], ', ') .. "}"
+  else
+    "{" .. table.concat(list, ', ') .. "}"
+
+format_value = (val, level) ->
+  if #val == 0
+    '{}'
+  elseif type(val[1]) == 'table'
+    rows = [indent format_list(row), level + 1 for row in *val]
+    table.insert rows, 1, '{'
+    table.insert rows, indent('}', level)
+    table.concat rows, '\n'
+  else
+    format_list(val)
+
+{
+  module_name: 'Strain'
+
+  test_helpers: [[
+
+  starts_with = (str, prefix) ->
+    str\sub(1, #prefix) == prefix
+
+  contains = (list, element) ->
+    for item in *list
+      if item == element
+        return true
+    false
+]]
+
+  generate_test: (case, level) ->
+
+
+    lines = {
+      "result = Strain.#{case.property} #{format_value(case.input.list, level)}, #{format_predicate case.input.predicate}"
+      "expected = #{format_value(case.expected, level)}"
+      "assert.are.same expected, result"
+    }
+
+    table.concat [indent line, level for line in *lines], '\n'
+}

exercises/practice/strain/.meta/tests.toml

@@ -0,0 +1,52 @@
+# 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.
+
+[26af8c32-ba6a-4eb3-aa0a-ebd8f136e003]
+description = "keep on empty list returns empty list"
+
+[f535cb4d-e99b-472a-bd52-9fa0ffccf454]
+description = "keeps everything"
+
+[950b8e8e-f628-42a8-85e2-9b30f09cde38]
+description = "keeps nothing"
+
+[92694259-6e76-470c-af87-156bdf75018a]
+description = "keeps first and last"
+
+[938f7867-bfc7-449e-a21b-7b00cbb56994]
+description = "keeps neither first nor last"
+
+[8908e351-4437-4d2b-a0f7-770811e48816]
+description = "keeps strings"
+
+[2728036b-102a-4f1e-a3ef-eac6160d876a]
+description = "keeps lists"
+
+[ef16beb9-8d84-451a-996a-14e80607fce6]
+description = "discard on empty list returns empty list"
+
+[2f42f9bc-8e06-4afe-a222-051b5d8cd12a]
+description = "discards everything"
+
+[ca990fdd-08c2-4f95-aa50-e0f5e1d6802b]
+description = "discards nothing"
+
+[71595dae-d283-48ca-a52b-45fa96819d2f]
+description = "discards first and last"
+
+[ae141f79-f86d-4567-b407-919eaca0f3dd]
+description = "discards neither first nor last"
+
+[daf25b36-a59f-4f29-bcfe-302eb4e43609]
+description = "discards strings"
+
+[a38d03f9-95ad-4459-80d1-48e937e4acaf]
+description = "discards lists"

exercises/practice/strain/strain.moon

@@ -0,0 +1,7 @@
+{
+  keep: (list, predicate) ->
+    error 'Implement me'
+  
+  discard: (list, predicate) ->
+    error 'Implement me'
+}

exercises/practice/strain/strain_spec.moon

@@ -0,0 +1,106 @@
+Strain = require 'strain'
+
+describe 'strain', ->
+  starts_with = (str, prefix) ->
+    str\sub(1, #prefix) == prefix
+
+  contains = (list, element) ->
+    for item in *list
+      if item == element
+        return true
+    false
+
+  it 'keep on empty list returns empty list', ->
+    result = Strain.keep {}, (_) -> true
+    expected = {}
+    assert.are.same expected, result
+
+  pending 'keeps everything', ->
+    result = Strain.keep {1, 3, 5}, (_) -> true
+    expected = {1, 3, 5}
+    assert.are.same expected, result
+
+  pending 'keeps nothing', ->
+    result = Strain.keep {1, 3, 5}, (_) -> false
+    expected = {}
+    assert.are.same expected, result
+
+  pending 'keeps first and last', ->
+    result = Strain.keep {1, 2, 3}, (num) -> num % 2 == 1
+    expected = {1, 3}
+    assert.are.same expected, result
+
+  pending 'keeps neither first nor last', ->
+    result = Strain.keep {1, 2, 3}, (num) -> num % 2 == 0
+    expected = {2}
+    assert.are.same expected, result
+
+  pending 'keeps strings', ->
+    result = Strain.keep {'apple', 'zebra', 'banana', 'zombies', 'cherimoya', 'zealot'}, (str) -> starts_with str, 'z'
+    expected = {'zebra', 'zombies', 'zealot'}
+    assert.are.same expected, result
+
+  pending 'keeps lists', ->
+    result = Strain.keep {
+      {1, 2, 3}
+      {5, 5, 5}
+      {5, 1, 2}
+      {2, 1, 2}
+      {1, 5, 2}
+      {2, 2, 1}
+      {1, 2, 5}
+    }, (list) -> contains list, 5
+    expected = {
+      {5, 5, 5}
+      {5, 1, 2}
+      {1, 5, 2}
+      {1, 2, 5}
+    }
+    assert.are.same expected, result
+
+  pending 'discard on empty list returns empty list', ->
+    result = Strain.discard {}, (_) -> true
+    expected = {}
+    assert.are.same expected, result
+
+  pending 'discards everything', ->
+    result = Strain.discard {1, 3, 5}, (_) -> true
+    expected = {}
+    assert.are.same expected, result
+
+  pending 'discards nothing', ->
+    result = Strain.discard {1, 3, 5}, (_) -> false
+    expected = {1, 3, 5}
+    assert.are.same expected, result
+
+  pending 'discards first and last', ->
+    result = Strain.discard {1, 2, 3}, (num) -> num % 2 == 1
+    expected = {2}
+    assert.are.same expected, result
+
+  pending 'discards neither first nor last', ->
+    result = Strain.discard {1, 2, 3}, (num) -> num % 2 == 0
+    expected = {1, 3}
+    assert.are.same expected, result
+
+  pending 'discards strings', ->
+    result = Strain.discard {'apple', 'zebra', 'banana', 'zombies', 'cherimoya', 'zealot'}, (str) -> starts_with str, 'z'
+    expected = {'apple', 'banana', 'cherimoya'}
+    assert.are.same expected, result
+
+  pending 'discards lists', ->
+    result = Strain.discard {
+      {1, 2, 3}
+      {5, 5, 5}
+      {5, 1, 2}
+      {2, 1, 2}
+      {1, 5, 2}
+      {2, 2, 1}
+      {1, 2, 5}
+    }, (list) -> contains list, 5
+    expected = {
+      {1, 2, 3}
+      {2, 1, 2}
+      {2, 2, 1}
+    }
+    assert.are.same expected, result