return to toplevel from a long running query after receiving Ctrl-C

src/prolog/machine/mod.rs

@@ -46,6 +46,7 @@ use std::io::{stdout, Read, Write};
 use std::mem;
 use std::ops::Index;
 use std::rc::Rc;
+use std::sync::atomic::AtomicBool;
 
 use termion::raw::IntoRawMode;
 
@@ -54,6 +55,10 @@ pub struct MachinePolicies {
     cut_policy: Box<CutPolicy>,
 }
 
+lazy_static! {
+    pub static ref INTERRUPT: AtomicBool = AtomicBool::new(false);
+}
+
 impl MachinePolicies {
     #[inline]
     fn new() -> Self {