diff --git a/ndc_lib/src/interpreter/mod.rs b/ndc_lib/src/interpreter/mod.rs
index 86e10db5..ba016353 100644
--- a/ndc_lib/src/interpreter/mod.rs
+++ b/ndc_lib/src/interpreter/mod.rs
@@ -65,8 +65,12 @@ impl Interpreter {
             }
         }
 
+        let checkpoint = self.analyser.checkpoint();
         for e in &mut expressions {
-            self.analyser.analyse(e)?;
+            if let Err(e) = self.analyser.analyse(e) {
+                self.analyser.restore(checkpoint);
+                return Err(e.into());
+            }
         }
 
         //dbg!(&expressions);
diff --git a/ndc_lib/src/interpreter/semantic/analyser.rs b/ndc_lib/src/interpreter/semantic/analyser.rs
index c0249ca0..44f0ac91 100644
--- a/ndc_lib/src/interpreter/semantic/analyser.rs
+++ b/ndc_lib/src/interpreter/semantic/analyser.rs
@@ -14,6 +14,14 @@ impl Analyser {
     pub fn from_scope_tree(scope_tree: ScopeTree) -> Self {
         Self { scope_tree }
     }
+
+    pub fn checkpoint(&self) -> ScopeTree {
+        self.scope_tree.clone()
+    }
+
+    pub fn restore(&mut self, checkpoint: ScopeTree) {
+        self.scope_tree = checkpoint;
+    }
 }
 
 impl Analyser {
@@ -559,7 +567,7 @@ fn extract_argument_arity(arguments: &ExpressionLocation) -> usize {
     values.len()
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct ScopeTree {
     current_scope_idx: usize,
     global_scope: Scope,
@@ -749,7 +757,7 @@ impl ScopeTree {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 struct Scope {
     parent_idx: Option<usize>,
     identifiers: Vec<(String, StaticType)>,