fix append func

Signed-off-by: Ava Hahn <ava@aidanis.online>

src/stl/append.rs

@@ -15,15 +15,19 @@
  */
 
 use crate::segment::{Ctr, Seg};
-use crate::sym::{SymTable};
+use crate::sym::SymTable;
 
-// Some essential operations below
 pub fn append_callback (ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
-    // if car is a list, append cdr
-    // otherwise create a list out of all arguments
     if let Ctr::Seg(ref s) = *ast.car {
         let mut temp = s.clone();
-        temp.append(ast.cdr.clone());
+        if let Ctr::Seg(ref list) = *ast.cdr {
+            list.circuit(&mut |c: &Ctr| -> bool {
+                temp.append(Box::new(c.clone()));
+                true
+            });
+        } else {
+            temp.append(Box::new(*ast.cdr.clone()));
+        }
         Ok(Ctr::Seg(temp))
     } else {
         let mut temp = Seg::new();