Implemented SymTable optimization for efficient variable updates

src/stl/control.rs

@@ -202,22 +202,10 @@ pub fn let_callback(ast: &Seg, syms: &mut SymTable) -> Result<Ctr, String> {
         return Err("evaluation failure".to_string());
     }
 
-    // we need to get any var declared from within the let eval forms
-    // those need to exist in the outside context
-    // TODO: make this more optimal
-    //     How can we skip iterations?
-    //     implement a counter for number of calls to def
-    //     store it inside the SymTable and Symbol
-    //     only re-insert into global scope what is most recent
-    for i in localsyms.iter() {
-        if !locals.contains(i.0) {
-            syms.insert(
-                i.0.clone(),
-                i.1.clone(),
-            );
-        }
+    for i in locals {
+        localsyms.remove(&i);
     }
-
+    syms.update(&mut localsyms);
     Ok((*result).clone())
 }