add stack functions

util.d

@@ -196,6 +196,37 @@ DLLPush(T, U)(T* list, U* node, U* nil)
 	}
 }
 
+struct Stack(T)
+{
+	Node!(T)* first;
+}
+
+void
+SPush(T, U)(T* stack, U* node, U* nil)
+{
+	if (CheckNil(nil, stack.first))
+	{
+		stack.first = node;
+		node.next = nil;
+	}
+	else
+	{
+		node.next = stack.first;
+		stack.first = node;
+	}
+}
+
+U*
+SPop(T, U)(T* stack, U* nil)
+{
+	U* node = stack.first;
+	if (!CheckNil(nil, stack.first))
+	{
+		stack.first = stack.first.next;
+	}
+	return node;
+}
+
 struct Node(T)
 {
 	Node!(T)* next;
@@ -934,4 +965,29 @@ unittest
 
 		table[100] = 100;
 	}
+
+	{ // Stack
+		Stack!(u32) stack;
+		Node!(u32) n1 = { value: 1 };
+		Node!(u32) n2 = { value: 2 };
+		Node!(u32) n3 = { value: 3 };
+
+		SPush(&stack, &n1, null);
+		SPush(&stack, &n2, null);
+		SPush(&stack, &n3, null);
+
+		u32 count = 3;
+		for (auto n = stack.first; !CheckNil(null, n); n = n.next, count -= 1)
+		{
+			assert(n.value == count);
+		}
+
+		count = 3;
+		for (auto n = SPop(&stack, cast(Node!(u32)*)null); !CheckNil(null, n); n = SPop(&stack, cast(Node!(u32)*)null), count -= 1)
+		{
+			assert(n.value == count);
+		}
+
+		assert(stack.first == null);
+	}
 }