simplify func return type, complete eval and process logic

src/func.rs

@@ -26,7 +26,7 @@ use crate::eval::eval;
 pub type FTable = HashMap<String, Rc<RefCell<Function>>>;
 
 // Standardized function signature for stdlib functions
-pub type InternalOperation = fn(Ast, Rc<RefCell<VTable>>, Rc<RefCell<FTable>>) -> Ast;
+pub type InternalOperation = fn(Ast, Rc<RefCell<VTable>>, Rc<RefCell<FTable>>) -> Ctr;
 pub struct ExternalOperation {
     // Un-evaluated abstract syntax tree
     // TODO: Intermediate evaluation to simplify branches with no argument in them
@@ -76,7 +76,7 @@ pub fn func_call(
     args: Ast,
     vars: Rc<RefCell<VTable>>,
     funcs: Rc<RefCell<FTable>>
-) -> Result<Ast, String> {
+) -> Result<Ctr, String> {
     let called_func = function.borrow_mut();
     let mut n_args: Ast = args.clone();
     if !called_func.eval_lazy {
@@ -151,15 +151,22 @@ pub fn func_call(
     match &called_func.function {
         Operation::Internal(f) => Ok((f)(n_args, vars, funcs)),
         Operation::External(f) => {
-            let mut temp = vars.borrow().clone();
             for n in 0..f.arg_syms.len() {
-                temp.insert(
+                vars.borrow().insert(
                     f.arg_syms[n].clone(),
                     Rc::new(list_idx(n_args.clone(), n as u128))
                 );
             }
 
-            eval(f.ast.clone(), Rc::new(RefCell::new(temp)), funcs, called_func.loose_syms)
+            let result = eval(f.ast.clone(), vars.clone(), funcs, called_func.loose_syms);
+            for n in 0..f.arg_syms.len() {
+                vars.borrow().remove(&f.arg_syms[n].clone());
+            }
+
+            match result {
+                Ok(r) => Ok(r.borrow().car),
+                Err(e) => Err(e)
+            }
         }
     }
 }