Data update

Task/Stack/Gleam/stack.gleam

@@ -0,0 +1,38 @@
+import gleam/option.{type Option, None, Some}
+
+/// Stack(a) is just an alias for a List(a)
+pub type Stack(a) =
+  List(a)
+
+/// An empty stack is an empty list.
+pub const empty = []
+
+/// is_empty(s) checks if the stack s is empty.
+pub fn is_empty(stack: Stack(a)) -> Bool {
+  case stack {
+    [] -> True
+    _ -> False
+  }
+}
+
+/// push(s,x) pushes the element x onto the stack s.
+pub fn push(stack: Stack(a), x: a) -> Stack(a) {
+  [x, ..stack]
+}
+
+/// peek(s) returns the TOS.
+pub fn peek(stack: Stack(a)) -> Result(a, Nil) {
+  case stack {
+    [] -> Error(Nil)
+    [h, ..] -> Ok(h)
+  }
+}
+
+/// pop(s) pops an element from the TOS, and returns that
+/// and the modified stack.
+pub fn pop(stack: Stack(a)) -> Result(#(a, Stack(a)), Nil) {
+  case stack {
+    [h, ..tl] -> Ok(#(h, tl))
+    _ -> Error(Nil)
+  }
+}