clear ball before setting it (#246)

src/prolog/machine/and_stack.rs

@@ -42,19 +42,27 @@ impl AndStack {
         AndStack(mem::replace(&mut self.0, vec![]))
     }
 
+    #[inline]    
     pub fn push(&mut self, global_index: usize, e: usize, cp: LocalCodePtr, n: usize) {
         let len = self.0.len();
         self.0.push(Frame::new(global_index, len, e, cp, n));
     }
 
+    #[inline]
     pub fn len(&self) -> usize {
         self.0.len()
     }
 
+    #[inline]
     pub fn clear(&mut self) {
         self.0.clear()
     }
     
+    #[inline]
+    pub fn top(&self) -> Option<&Frame> {
+        self.0.last()
+    }
+
     /* 
 
     // See MachineState::allocate for why this is commented out.

src/prolog/machine/machine_state.rs

@@ -486,7 +486,6 @@ pub(crate) trait CallPolicy: Any {
         machine_st.pstr_tr = machine_st.or_stack[b].pstr_tr;
 
         machine_st.pstr_trail.truncate(machine_st.pstr_tr);
-
         machine_st.heap.truncate(machine_st.or_stack[b].h);
 
         let attr_var_init_queue_b = machine_st.or_stack[b].attr_var_init_queue_b;
@@ -532,7 +531,6 @@ pub(crate) trait CallPolicy: Any {
         machine_st.pstr_tr = machine_st.or_stack[b].pstr_tr;
 
         machine_st.pstr_trail.truncate(machine_st.pstr_tr);
-
         machine_st.heap.truncate(machine_st.or_stack[b].h);
 
         let attr_var_init_queue_b = machine_st.or_stack[b].attr_var_init_queue_b;
@@ -578,8 +576,8 @@ pub(crate) trait CallPolicy: Any {
         let curr_pstr_tr = machine_st.pstr_tr;
 
         machine_st.unwind_pstr_trail(old_pstr_tr, curr_pstr_tr);
-        machine_st.pstr_tr = machine_st.or_stack[b].pstr_tr;
 
+        machine_st.pstr_tr = machine_st.or_stack[b].pstr_tr;
         machine_st.pstr_trail.truncate(machine_st.pstr_tr);
 
         machine_st.heap.truncate(machine_st.or_stack[b].h);

src/prolog/machine/machine_state_impl.rs

@@ -125,16 +125,14 @@ impl MachineState {
 
     pub(super) fn next_global_index(&self) -> usize {
         max(
-            if self.and_stack.len() > 0 {
-                self.and_stack[self.e].global_index
-            } else {
-                0
-            },
-            if self.b > 0 {
-                self.or_stack[self.b - 1].global_index
-            } else {
-                0
-            },
+            self.or_stack
+                .top()
+                .map(|or_fr| or_fr.global_index)
+                .unwrap_or(0),
+            self.and_stack
+                .top()
+                .map(|or_fr| or_fr.global_index)
+                .unwrap_or(0),
         ) + 1
     }
 
@@ -2039,8 +2037,11 @@ impl MachineState {
     }
 
     pub(super) fn set_ball(&mut self) {
+        self.ball.reset();
+
         let addr = self[temp_v!(1)].clone();
         self.ball.boundary = self.heap.h;
+
         copy_term(
             CopyBallTerm::new(&mut self.and_stack, &mut self.heap, &mut self.ball.stub),
             addr,

src/prolog/toplevel.pl

@@ -42,8 +42,7 @@
     (  expand_goals(Term0, Term) -> true
     ;  Term = Term0
     ),
-    (  '$get_b_value'(B), call(Term),
-       '$write_eqs_and_read_input'(B, VarList),
+    (  '$get_b_value'(B), call(Term), '$write_eqs_and_read_input'(B, VarList),
        !
     ;  write('false.'), nl
     ).