From d7deda50789947b17b315b54bb15167f8694bca6 Mon Sep 17 00:00:00 2001
From: Hunam <hunam@disroot.org>
Date: Thu, 23 Dec 2021 14:16:29 +0100
Subject: [PATCH] vlib: add an `adt` module (Abstract Data Types) (#12901)

---
 vlib/adt/README.md    |  9 ++++++++
 vlib/adt/stack.v      | 36 ++++++++++++++++++++++++++++++
 vlib/adt/stack_test.v | 52 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+)
 create mode 100644 vlib/adt/README.md
 create mode 100644 vlib/adt/stack.v
 create mode 100644 vlib/adt/stack_test.v

diff --git a/vlib/adt/README.md b/vlib/adt/README.md
new file mode 100644
index 0000000000..da6acd151d
--- /dev/null
+++ b/vlib/adt/README.md
@@ -0,0 +1,9 @@
+# adt
+
+A library providing common ADTs (Abstract Data Type) implementations which have proved useful in a
+great variety of applications.
+
+## implementations
+
+- [x] Stack (LIFO)
+- [ ] ...
diff --git a/vlib/adt/stack.v b/vlib/adt/stack.v
new file mode 100644
index 0000000000..7e42842eff
--- /dev/null
+++ b/vlib/adt/stack.v
@@ -0,0 +1,36 @@
+module adt
+
+pub struct Stack<T> {
+mut:
+	elements []T
+}
+
+// is_empty checks if the stack is empty
+pub fn (stack Stack<T>) is_empty() bool {
+	return stack.elements.len == 0
+}
+
+// len returns the length of the stack
+pub fn (stack Stack<T>) len() int {
+	return stack.elements.len
+}
+
+// peek returns the top of the stack
+pub fn (stack Stack<T>) peek() ?T {
+	return if !stack.is_empty() { stack.elements.last() } else { error('Stack is empty') }
+}
+
+// push adds an element to the top of the stack
+pub fn (mut stack Stack<T>) push(item T) {
+	stack.elements << item
+}
+
+// pop removes the element at the top of the stack and returns it
+pub fn (mut stack Stack<T>) pop() ?T {
+	return if !stack.is_empty() { stack.elements.pop() } else { error('Stack is empty') }
+}
+
+// str returns a string representation of the stack
+pub fn (stack Stack<T>) str() string {
+	return stack.elements.str()
+}
diff --git a/vlib/adt/stack_test.v b/vlib/adt/stack_test.v
new file mode 100644
index 0000000000..84c1a2a761
--- /dev/null
+++ b/vlib/adt/stack_test.v
@@ -0,0 +1,52 @@
+import adt
+
+fn test_is_empty() {
+	mut stack := adt.Stack<int>{}
+	assert stack.is_empty() == true
+	stack.push(1)
+	assert stack.is_empty() == false
+}
+
+fn test_len() ? {
+	mut stack := adt.Stack<int>{}
+	assert stack.len() == 0
+	stack.push(1)
+	assert stack.len() == 1
+	stack.pop() ?
+	assert stack.len() == 0
+}
+
+fn test_peek() ? {
+	mut stack := adt.Stack<int>{}
+	stack.push(1)
+	assert stack.peek() ? == 1
+	stack.push(2)
+	assert stack.peek() ? == 2
+	stack = adt.Stack<int>{}
+	stack.peek() or { return }
+	assert false
+}
+
+fn test_push() ? {
+	mut stack := adt.Stack<int>{}
+	stack.push(1)
+	assert stack.peek() ? == 1
+	stack.push(2)
+	assert stack.peek() ? == 2
+	stack.push(3)
+	assert stack.peek() ? == 3
+}
+
+fn test_pop() ? {
+	mut stack := adt.Stack<int>{}
+	stack.push(1)
+	stack.push(2)
+	stack.push(3)
+	assert stack.pop() ? == 3
+	stack.push(4)
+	assert stack.pop() ? == 4
+	assert stack.pop() ? == 2
+	stack = adt.Stack<int>{}
+	stack.pop() or { return }
+	assert false
+}