From 7885da4e2979ef560e99ed05dff00da9f6a9adaf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alexander=20W=C3=BChr?= <alex@pnyhf.eu>
Date: Thu, 19 Sep 2024 09:09:22 +0200
Subject: [PATCH] feat: implement stack

---
 manifest.toml            | 11 +++++
 src/fortheck.gleam       |  5 ---
 src/fortheck/error.gleam |  4 ++
 src/fortheck/stack.gleam | 61 ++++++++++++++++++++++++++
 test/fortheck_test.gleam |  7 ---
 test/stack_test.gleam    | 92 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 168 insertions(+), 12 deletions(-)
 create mode 100644 manifest.toml
 delete mode 100644 src/fortheck.gleam
 create mode 100644 src/fortheck/error.gleam
 create mode 100644 src/fortheck/stack.gleam
 create mode 100644 test/stack_test.gleam

diff --git a/manifest.toml b/manifest.toml
new file mode 100644
index 0000000..e851620
--- /dev/null
+++ b/manifest.toml
@@ -0,0 +1,11 @@
+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "gleam_stdlib", version = "0.40.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "86606B75A600BBD05E539EB59FABC6E307EEEA7B1E5865AFB6D980A93BCB2181" },
+  { name = "gleeunit", version = "1.2.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "F7A7228925D3EE7D0813C922E062BFD6D7E9310F0BEE585D3A42F3307E3CFD13" },
+]
+
+[requirements]
+gleam_stdlib = { version = ">= 0.34.0 and < 2.0.0" }
+gleeunit = { version = ">= 1.0.0 and < 2.0.0" }
diff --git a/src/fortheck.gleam b/src/fortheck.gleam
deleted file mode 100644
index 5299693..0000000
--- a/src/fortheck.gleam
+++ /dev/null
@@ -1,5 +0,0 @@
-import gleam/io
-
-pub fn main() {
-  io.println("Hello from fortheck!")
-}
diff --git a/src/fortheck/error.gleam b/src/fortheck/error.gleam
new file mode 100644
index 0000000..f1ee495
--- /dev/null
+++ b/src/fortheck/error.gleam
@@ -0,0 +1,4 @@
+pub type Error {
+  StackOverflow
+  StackUnderflow
+}
diff --git a/src/fortheck/stack.gleam b/src/fortheck/stack.gleam
new file mode 100644
index 0000000..321b679
--- /dev/null
+++ b/src/fortheck/stack.gleam
@@ -0,0 +1,61 @@
+import fortheck/error.{type Error, StackOverflow, StackUnderflow}
+import gleam/bool
+import gleam/list
+import gleam/result
+
+pub opaque type Stack(a) {
+  Stack(capacity: Int, length: Int, data: List(a))
+}
+
+pub fn new() -> Stack(a) {
+  Stack(131_072, 0, [])
+}
+
+pub fn from_list(list: List(a)) -> Result(Stack(a), Error) {
+  list.try_fold(over: list, from: new(), with: push)
+}
+
+pub fn to_list(stack: Stack(a)) -> List(a) {
+  list.reverse(stack.data)
+}
+
+pub fn push(onto stack: Stack(a), this item: a) -> Result(Stack(a), Error) {
+  use <- bool.guard(
+    when: stack.length >= stack.capacity,
+    return: Error(StackOverflow),
+  )
+
+  Ok(Stack(..stack, length: stack.length + 1, data: [item, ..stack.data]))
+}
+
+pub fn pop(from stack: Stack(a)) -> Result(#(a, Stack(a)), Error) {
+  case stack.data {
+    [] -> Error(StackUnderflow)
+    [x, ..xs] -> Ok(#(x, Stack(..stack, length: stack.length - 1, data: xs)))
+  }
+}
+
+pub fn try_pop(
+  from stack: Stack(a),
+  apply fun: fn(a, Stack(a)) -> Result(b, Error),
+) -> Result(b, Error) {
+  use #(item, stack) <- result.try(pop(from: stack))
+
+  fun(item, stack)
+}
+
+pub fn pop_2(from stack: Stack(a)) -> Result(#(#(a, a), Stack(a)), Error) {
+  use b, stack <- try_pop(from: stack)
+  use a, stack <- try_pop(from: stack)
+
+  Ok(#(#(a, b), stack))
+}
+
+pub fn try_pop_2(
+  from stack: Stack(a),
+  apply fun: fn(a, a, Stack(a)) -> Result(b, Error),
+) -> Result(b, Error) {
+  use #(#(a, b), stack) <- result.try(pop_2(from: stack))
+
+  fun(a, b, stack)
+}
diff --git a/test/fortheck_test.gleam b/test/fortheck_test.gleam
index 3831e7a..ecd12ad 100644
--- a/test/fortheck_test.gleam
+++ b/test/fortheck_test.gleam
@@ -1,12 +1,5 @@
 import gleeunit
-import gleeunit/should
 
 pub fn main() {
   gleeunit.main()
 }
-
-// gleeunit test functions end in `_test`
-pub fn hello_world_test() {
-  1
-  |> should.equal(1)
-}
diff --git a/test/stack_test.gleam b/test/stack_test.gleam
new file mode 100644
index 0000000..f80dcab
--- /dev/null
+++ b/test/stack_test.gleam
@@ -0,0 +1,92 @@
+import fortheck/error
+import fortheck/stack
+import gleam/iterator
+import gleam/pair
+import gleam/result
+import gleeunit
+import gleeunit/should
+
+pub fn main() {
+  gleeunit.main()
+}
+
+pub fn new_test() {
+  stack.new()
+  |> stack.to_list
+  |> should.equal([])
+}
+
+pub fn push_test() {
+  stack.new()
+  |> stack.push(123)
+  |> should.be_ok
+  |> stack.push(456)
+  |> should.be_ok
+  |> stack.to_list
+  |> should.equal([123, 456])
+}
+
+pub fn push_stack_overflow_test() {
+  iterator.range(1, 131_072)
+  |> iterator.try_fold(stack.new(), stack.push)
+  |> should.be_ok
+  |> stack.push(1)
+  |> should.be_error
+  |> should.equal(error.StackOverflow)
+}
+
+pub fn from_list_test() {
+  [123, 456]
+  |> stack.from_list
+  |> should.be_ok
+  |> stack.to_list
+  |> should.equal([123, 456])
+}
+
+pub fn pop_stack_underflow_test() {
+  stack.new()
+  |> stack.pop
+  |> should.be_error
+  |> should.equal(error.StackUnderflow)
+}
+
+pub fn pop_test() {
+  let assert Ok(stack) = stack.from_list([1, 2, 3])
+
+  stack
+  |> stack.pop
+  |> should.be_ok
+  |> pair.first
+  |> should.equal(3)
+
+  {
+    use a, _ <- stack.try_pop(stack)
+    Ok(a)
+  }
+  |> should.be_ok
+  |> should.equal(3)
+}
+
+pub fn pop_2_test() {
+  let assert Ok(stack) = stack.from_list([1, 2, 3])
+
+  stack
+  |> stack.pop_2
+  |> should.be_ok
+  |> pair.first
+  |> should.equal(#(2, 3))
+
+  {
+    use a, b, _ <- stack.try_pop_2(stack)
+    Ok(#(a, b))
+  }
+  |> should.be_ok
+  |> should.equal(#(2, 3))
+}
+
+pub fn pop_2_stack_underflow_test() {
+  stack.from_list([1])
+  |> result.try(stack.pop_2)
+  |> should.be_error
+  |> should.equal(error.StackUnderflow)
+}