From 5d6ca7a88e4c9bf4bc8793d1e8184c90ef109275 Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Sun, 19 Apr 2020 12:58:44 -0600
Subject: [PATCH] throw '' whenever an interrupt is made (#365, #366)

---
 src/prolog/lib/iso_ext.pl                |  4 ++--
 src/prolog/machine/machine_errors.rs     | 12 ++++++++++++
 src/prolog/machine/machine_state_impl.rs | 11 +++++++++--
 src/prolog/toplevel.pl                   |  3 +++
 4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/prolog/lib/iso_ext.pl b/src/prolog/lib/iso_ext.pl
index a1944d13..68708250 100644
--- a/src/prolog/lib/iso_ext.pl
+++ b/src/prolog/lib/iso_ext.pl
@@ -22,9 +22,9 @@ bb_put(Key, _) :- throw(error(type_error(atom, Key), bb_put/2)).
 bb_b_put(Key, NewValue) :-
     (  '$bb_get_with_offset'(Key, OldValue, OldOffset) ->
        call_cleanup((store_global_var_with_offset(Key, NewValue) ; false),
-		    reset_global_var_at_offset(Key, OldValue, OldOffset))
+		            reset_global_var_at_offset(Key, OldValue, OldOffset))
     ;  call_cleanup((store_global_var_with_offset(Key, NewValue) ; false),
-		    reset_global_var_at_key(Key))
+		            reset_global_var_at_key(Key))
     ).
 
 store_global_var_with_offset(Key, Value) :- '$store_global_var_with_offset'(Key, Value).
diff --git a/src/prolog/machine/machine_errors.rs b/src/prolog/machine/machine_errors.rs
index c5173afc..68b7a3ff 100644
--- a/src/prolog/machine/machine_errors.rs
+++ b/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())]);
diff --git a/src/prolog/machine/machine_state_impl.rs b/src/prolog/machine/machine_state_impl.rs
index 941fa4cb..dfcb08be 100644
--- a/src/prolog/machine/machine_state_impl.rs
+++ b/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;
 	    }
 
diff --git a/src/prolog/toplevel.pl b/src/prolog/toplevel.pl
index d826b1b5..099bc9f9 100644
--- a/src/prolog/toplevel.pl
+++ b/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.
-- 
2.54.0