throw '' whenever an interrupt is made (#365, #366)

src/prolog/machine/machine_errors.rs

@@ -154,6 +154,18 @@ impl MachineError {
         )
     }
 
+    #[inline]
+    pub(super)
+    fn interrupt_error() -> Self {
+        let stub = functor!("$interrupt_thrown");
+        
+        MachineError {
+            stub,
+            location: None,
+            from: ErrorProvenance::Received,
+        }
+    }
+
     pub(super)
     fn evaluation_error(eval_error: EvalError) -> Self {
         let stub = functor!("evaluation_error", [atom(eval_error.as_str())]);

src/prolog/machine/machine_state_impl.rs

@@ -3089,6 +3089,14 @@ impl MachineState {
         self.p += 1;
     }
 
+    fn throw_interrupt_exception(&mut self) {
+        let err = MachineError::interrupt_error();
+        let src = functor!("repl");
+        let err = self.error_form(err, src);
+
+        self.throw_exception(err);
+    }
+
     fn handle_call_clause(
         &mut self,
         indices: &mut IndexStore,
@@ -3105,8 +3113,7 @@ impl MachineState {
 	    let interrupted = INTERRUPT.load(std::sync::atomic::Ordering::Relaxed);
 
 	    if INTERRUPT.compare_and_swap(interrupted, false, std::sync::atomic::Ordering::Relaxed) {
-	        self.reset();
-	        self.fail = true;
+            self.throw_interrupt_exception();
 	        return;
 	    }
 

src/prolog/toplevel.pl

@@ -214,6 +214,9 @@ gather_goals([Var = Value | Pairs], VarList, Goals) :-
     ).
 
 print_exception(E) :-
+    (  E == error('$interrupt_thrown', repl) -> nl % print the exception on a newline to evade "^C".
+    ;  true
+    ),
     write_term('caught: ', [quoted(false), max_depth(20)]),
     writeq(E),
     nl.