From 7aa97816c0c54fb050b5c1a5e2c94dc25c544cfe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A1s=20B=20Nagy?=
 <20251272+BNAndras@users.noreply.github.com>
Date: Mon, 15 Jan 2024 18:19:22 -0800
Subject: [PATCH] Add boolean chain approach

---
 .../leap/.approaches/boolean-chain/content.md | 36 +++++++++++++++++++
 .../.approaches/boolean-chain/snippet.txt     |  1 +
 .../practice/leap/.approaches/config.json     | 18 ++++++++++
 .../practice/leap/.approaches/introduction.md | 25 +++++++++++++
 4 files changed, 80 insertions(+)
 create mode 100644 exercises/practice/leap/.approaches/boolean-chain/content.md
 create mode 100644 exercises/practice/leap/.approaches/boolean-chain/snippet.txt
 create mode 100644 exercises/practice/leap/.approaches/config.json
 create mode 100644 exercises/practice/leap/.approaches/introduction.md

diff --git a/exercises/practice/leap/.approaches/boolean-chain/content.md b/exercises/practice/leap/.approaches/boolean-chain/content.md
new file mode 100644
index 0000000..e924104
--- /dev/null
+++ b/exercises/practice/leap/.approaches/boolean-chain/content.md
@@ -0,0 +1,36 @@
+# Boolean chaining
+
+```pyret
+fun leap(year):
+  fun year-is-divisible-by(divisor):
+    num-equal(num-modulo(year, divisor), 0)
+  end
+
+  year-is-divisible-by(4) and (not(year-is-divisible-by(100)) or year-is-divisible-by(400))
+end
+```
+
+This approach uses the Boolean operators `and` and `or` to chain together values from two Boolean expressions, creating a Boolean value.
+The `and` operator returns `true` when both sides are true but `false` otherwise.
+The `or` operator returns `false` when both sides are false but `true` otherwise.
+
+|   n1  |   n2  | n1 OR n2 | n1 AND n2 |
+| ----- | ----- | -------  | --------- |
+| false | false |    false |     false |
+| false | true  |     true |     false |
+| true  | false |     true |     false |
+| true  | true  |     true |      true | 
+
+Both operators can short-circuit which means in some scenarios, the operators don't evaluate the expression to the right.
+For `and`, if the left side produces `false`, that value is returned immediately.
+For `or`, if the left side produces `true`, that value is returned immediately.
+
+We can now test if a year is evenly divisible by 4, 100, and 400. 
+All leap years are divisible by 4 but not by 100 unless they're also divisible by 100.
+
+| year | year % 4 == 0 | year % 100 != 0 | year % 400 == 0 | is leap year |
+| ---- | ------------- | --------------- | --------------- | ------------ |
+| 2020 |          true |            true | (not evaluated) |         true |
+| 2019 |         false | (not evaluated) | (not evaluated) |        false |
+| 2000 |          true |           false |            true |         true |
+| 1900 |          true |           false |           false |        false |
diff --git a/exercises/practice/leap/.approaches/boolean-chain/snippet.txt b/exercises/practice/leap/.approaches/boolean-chain/snippet.txt
new file mode 100644
index 0000000..311c8dd
--- /dev/null
+++ b/exercises/practice/leap/.approaches/boolean-chain/snippet.txt
@@ -0,0 +1 @@
+PLACEHOLDER
\ No newline at end of file
diff --git a/exercises/practice/leap/.approaches/config.json b/exercises/practice/leap/.approaches/config.json
new file mode 100644
index 0000000..683145d
--- /dev/null
+++ b/exercises/practice/leap/.approaches/config.json
@@ -0,0 +1,18 @@
+{
+  "introduction": {
+    "authors": [
+      "BNAndras"
+    ]
+  },
+  "approaches": [
+    {
+      "uuid": "2f53896f-b3e7-4c7d-be3a-a3342087826e",
+      "slug": "boolean-chain",
+      "title": "Boolean Chaining",
+      "blurb": "Use operators to check boolean values in a chain",
+      "authors": [
+        "BNAndras"
+      ]
+    }
+  ]
+}
diff --git a/exercises/practice/leap/.approaches/introduction.md b/exercises/practice/leap/.approaches/introduction.md
new file mode 100644
index 0000000..01d2f24
--- /dev/null
+++ b/exercises/practice/leap/.approaches/introduction.md
@@ -0,0 +1,25 @@
+# Introduction
+
+There are two approaches highlighted here for his exercise.
+Both involve checking if a year is evenly divisible by 4, 100, and 400 using [num-modulo][num-modulo].
+
+## General guidance
+
+Regardless of the approach chosen, this exercise requires students to use Boolean logic to decide if a given year is a leap year.
+
+## Approach: Boolean chaining
+
+```pyret
+fun leap(year):
+  fun year-is-divisible-by(divisor):
+    num-equal(num-modulo(year, divisor), 0)
+  end
+
+  year-is-divisible-by(4) and (not(year-is-divisible-by(100)) or year-is-divisible-by(400))
+end
+```
+
+For more information, check the [Boolean chain approach][approach-boolean-chain].
+
+[num-modulo]: https://pyret.org/docs/latest/numbers.html#%28part._numbers_num-modulo%29
+[approach-boolean-chain]: https://exercism.org/tracks/pyret/exercises/leap/approaches/boolean-chain
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