1 files changed, 36 insertions, 2 deletions

diff --git a/src/context.rs b/src/context.rs
index e4cd5c2..7484a1f 100644
--- a/src/context.rs
+++ b/src/context.rs
@@ -5,11 +5,12 @@ use crate::{Identifier,IdentifierValue};
 pub type Context = HashMap<String,Value>;
 
 pub trait MappedStructure {
-    fn get_value(&self, id: &Identifier) -> Option<Value>;
+    fn get_value(&self, id: &[IdentifierValue]) -> Option<Value>;
+
 }
 
 impl MappedStructure for Context {
-    fn get_value(&self, id: &Identifier) -> Option<Value> {
+    fn get_value(&self, id: &[IdentifierValue]) -> Option<Value> {
         if id.len() == 0 {
             return None;
         }
@@ -37,6 +38,39 @@ impl MappedStructure for Context {
     }
 }
 
+pub struct StatefulContext<'a, T: MappedStructure> {
+    root: &'a T,
+    current: &'a T,
+}
+
+impl<'a, T: MappedStructure> StatefulContext<'a, T> {
+    pub fn root( root: &'a T ) -> Self {
+        Self {
+            root, current: root,
+        }
+    }
+
+    pub fn local(&self, current: &'a T ) -> Self {
+        Self {
+            root: self.root,
+            current
+        }
+    }
+}
+
+impl<'a, T: MappedStructure> MappedStructure for StatefulContext<'a,T> {
+    fn get_value(&self, id: &[IdentifierValue]) -> Option<Value> {
+        if id.is_empty() {
+            return None;
+        }
+        if id[0] == IdentifierValue::Root {
+            self.root.get_value( &id[1..] )
+        } else {
+            self.current.get_value( id )
+        }
+    }
+}
+
 #[derive(Debug,Clone)]
 pub enum Value {
     Dictionary(Context),