3 files changed, 77 insertions, 0 deletions

diff --git a/stack/src/main.adb b/stack/src/main.adb
new file mode 100644
index 0000000..977a46b
--- /dev/null
+++ b/stack/src/main.adb
@@ -0,0 +1,20 @@
+with Ada.Assertions; use Ada.Assertions;
+with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
+with Ada.Text_IO; use Ada.Text_IO;
+
+with Stack;
+
+procedure Main is
+   package IntStack is new Stack (Integer);
+   S : IntStack.Stack;
+   Val : Integer;
+begin
+   Put_Line ("Hello world!");
+   for I in 1 .. 5 loop
+      IntStack.Push (S, I);
+   end loop;
+   while not IntStack.Empty (S) loop
+      Assert (IntStack.Pop (S, Val));
+      Put_Line (Val'Image);
+   end loop;
+end Main;
diff --git a/stack/src/stack.adb b/stack/src/stack.adb
new file mode 100644
index 0000000..4dc8fb1
--- /dev/null
+++ b/stack/src/stack.adb
@@ -0,0 +1,31 @@
+with Ada.Unchecked_Deallocation;
+
+package body Stack is
+   procedure Free is new Ada.Unchecked_Deallocation (Node, Node_Access);
+
+   procedure Push (S : in out Stack; Val : T) is
+      New_Top : Node_Access := new Node;
+   begin
+      New_Top.Val := Val;
+      New_Top.Bottom := S.Top;
+      S.Top := New_Top;
+   end Push;
+
+   function Pop (S : in out Stack; Val : out T) return Boolean is
+      Old_Top : Node_Access := S.Top;
+   begin
+      if Old_Top /= null then
+         Val := Old_Top.Val;
+         S.Top := Old_Top.Bottom;
+         Free (Old_Top);
+         return True;
+      else
+         return False;
+      end if;
+   end Pop;
+
+   function Empty (S : Stack) return Boolean is
+   begin
+      return S.Top = null;
+   end Empty;
+end Stack;
diff --git a/stack/src/stack.ads b/stack/src/stack.ads
new file mode 100644
index 0000000..4f390e3
--- /dev/null
+++ b/stack/src/stack.ads
@@ -0,0 +1,26 @@
+generic
+   type T is private;
+package Stack is
+   type Stack is private;
+
+   -- Push a value into the stack.
+   procedure Push (S : in out Stack; Val : T);
+
+   -- Pop a value from the stack.
+   function Pop (S : in out Stack; Val : out T) return Boolean;
+
+   -- Return true if the stack is empty, false otherwise.
+   function Empty (S : Stack) return Boolean;
+private
+   type Node;
+   type Node_Access is access Node;
+
+   type Node is record
+      Val    : T;
+      Bottom : Node_Access;
+   end record;
+
+   type Stack is record
+      Top : Node_Access;
+   end record;
+end Stack;