Small fixes

SLS_Rust/sls/src/interpreter.rs

@@ -124,7 +124,7 @@ impl InterpreterState {
     }
 
     pub fn stack_top(&self) -> Option<&StackValue> {
-        self.stack.get(0)
+        self.stack.get(self.stack.len() - 1)
     }
 }
 

SLS_Rust/sls/src/repl.rs

@@ -67,7 +67,8 @@ pub fn repl() -> i32 {
             LexResult::Ok(tokens) => {
                 for token in tokens {
                     if !interpreter.execute(token) {
-                        return 1;
+                        println!("A runtime error occured!");
+                        break;
                     }
                 }