fix case for 0 arg function calls

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

src/config.rs

@@ -23,10 +23,12 @@ use crate::stl::get_stdlib;
 use crate::vars::{define, VTable};
 use std::cell::RefCell;
 use std::fs;
+use std::io::{self, Write};
 use std::rc::Rc;
 
 fn prompt_default_callback(_: Ast, _: Rc<RefCell<VTable>>, _: Rc<RefCell<FTable>>) -> Ctr {
     print!("λ ");
+    io::stdout().flush().unwrap();
     return Ctr::None;
 }