Starting to separate the context and parsed tokens into their own modules.

src/context/list.rs

@@ -0,0 +1,66 @@
+use std::fmt::Debug;
+
+#[derive(Debug, Clone)]
+pub struct List<'parent, T> {
+    data: T,
+    parent: Link<'parent, T>,
+}
+
+type Link<'parent, T> = Option<&'parent List<'parent, T>>;
+
+impl<'parent, T> List<'parent, T> {
+    pub fn new(first_item: T) -> Self {
+        Self {
+            data: first_item,
+            parent: None,
+        }
+    }
+
+    pub fn get_data(&self) -> &T {
+        &self.data
+    }
+
+    pub fn get_parent(&'parent self) -> Link<'parent, T> {
+        self.parent
+    }
+
+    pub fn iter(&self) -> Iter<'_, T> {
+        Iter { next: Some(self) }
+    }
+}
+
+pub trait ListType<'parent, T> {
+    fn push(&'parent self, item: T) -> List<'parent, T>;
+}
+
+impl<'parent, T> ListType<'parent, T> for List<'parent, T> {
+    fn push(&'parent self, item: T) -> Self {
+        Self {
+            data: item,
+            parent: Some(self),
+        }
+    }
+}
+
+impl<'parent, T> ListType<'parent, T> for Link<'parent, T> {
+    fn push(&'parent self, item: T) -> List<'parent, T> {
+        List {
+            data: item,
+            parent: *self,
+        }
+    }
+}
+
+pub struct Iter<'a, T> {
+    next: Link<'a, T>,
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let ret = self.next.map(|link| link.get_data());
+        self.next = self.next.map(|link| link.get_parent()).flatten();
+        ret
+    }
+}