diff --git a/src/mango/io/fortest/stringreader.rs b/src/mango/io/fortest/stringreader.rs
index fd5a1d4c..9419fb5a 100644
--- a/src/mango/io/fortest/stringreader.rs
+++ b/src/mango/io/fortest/stringreader.rs
@@ -52,6 +52,10 @@ impl Reader for StringReader {
             };
         })
     }
+
+    fn get_progress(&self) -> usize {
+        self.index
+    }
 }
 
 // TODO: tests (spaces, end)
diff --git a/src/mango/io/typ.rs b/src/mango/io/typ.rs
index 5f8fd9f0..6aedf0d5 100644
--- a/src/mango/io/typ.rs
+++ b/src/mango/io/typ.rs
@@ -17,6 +17,10 @@ pub trait Reader: Debug {
     ///
     /// This has to eventually return EOF, and keep returning EOF forever after that.
     fn matches(&mut self, subpattern: &str) -> ReaderResult;
+
+    /// Return a number that can be used to check whether the state has changed.
+    /// This need not correspond to a specific position, but should be unique for the progress.
+    fn get_progress(&self) -> usize;
 }
 
 pub trait Writer {
diff --git a/src/mango/util/collection/mod.rs b/src/mango/util/collection/mod.rs
index 5f327a57..f31304ed 100644
--- a/src/mango/util/collection/mod.rs
+++ b/src/mango/util/collection/mod.rs
@@ -1,2 +1,5 @@
 pub mod queue;
 pub use self::queue::Queue;
+
+pub mod stack;
+pub use self::stack::Stack;
diff --git a/src/mango/util/collection/queue.rs b/src/mango/util/collection/queue.rs
index 02996c44..8eb43ec1 100644
--- a/src/mango/util/collection/queue.rs
+++ b/src/mango/util/collection/queue.rs
@@ -1,23 +1,27 @@
-use std::collections::VecDeque;
 
-/// A one-ended queue.
-/// This is just a wrapper around deque so nobody pushes or pops the wrong end.
+/// A one-ended queue. See also [Stack].
+/// This is just a wrapper around vec so nobody pushes or pops the wrong end.
 pub struct Queue<T> {
-    deque: VecDeque<T>,
+    items: Vec<T>,
 }
 
 impl<T> Queue<T> {
     pub fn new() -> Self {
         Queue {
-            deque: VecDeque::with_capacity(16),
+            items: Vec::with_capacity(16),
         }
     }
 
     pub fn push(&mut self, value: T) {
-        self.deque.push_back(value)
+        self.items.push(value)
     }
 
     pub fn pop(&mut self) -> Option<T> {
-        self.deque.pop_front()
+        self.items.pop()
+    }
+
+    /// Moves all the elements from a vector into the queue.
+    pub fn append(&mut self, mut other: Vec<T>) {
+        self.items.append(&mut other);
     }
 }
diff --git a/src/mango/util/collection/stack.rs b/src/mango/util/collection/stack.rs
new file mode 100644
index 00000000..055c0a18
--- /dev/null
+++ b/src/mango/util/collection/stack.rs
@@ -0,0 +1,27 @@
+use std::collections::VecDeque;
+
+/// A one-ended stack. See also [Queue].
+/// This is just a wrapper around deque so nobody pushes or pops the wrong end.
+pub struct Stack<T> {
+    items: VecDeque<T>,
+}
+
+impl<T> Stack<T> {
+    pub fn new() -> Self {
+        Stack {
+            items: VecDeque::with_capacity(16),
+        }
+    }
+
+    pub fn push(&mut self, value: T) {
+        self.items.push_back(value)
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        self.items.pop_back()
+    }
+
+    pub fn borrow_mut(&mut self) -> Option<&mut T> {
+        self.items.back_mut()
+    }
+}