fix term expansion bug

src/prolog/read.rs

@@ -53,7 +53,7 @@ impl MachineState {
         let mut parser = Parser::new(inner, atom_tbl, self.flags);
         let term = parser.read_term(composite_op!(op_dir))?;
 
-        Ok(write_term_to_heap(&term, self).0)
+        Ok(write_term_to_heap(&term, self).heap_loc)
     }
 }
 
@@ -73,9 +73,17 @@ fn modify_head_of_queue(machine_st: &mut MachineState, queue: &mut SubtermDeque,
     }
 }
 
-pub(crate) fn write_term_to_heap(term: &Term, machine_st: &mut MachineState) -> (usize, HeapVarDict) {
-    let h = machine_st.heap.h;
+pub(crate) struct TermWriteResult {
+    pub(crate) heap_loc: usize,
+    pub(crate) max_var_length: usize, // maximum length of the variable names encountered.
+    pub(crate) var_dict: HeapVarDict,        
+}
 
+pub(crate) fn write_term_to_heap(term: &Term, machine_st: &mut MachineState) -> TermWriteResult
+{
+    let heap_loc = machine_st.heap.h;
+
+    let mut max_var_length = 0;
     let mut queue = SubtermDeque::new();
     let mut var_dict = HeapVarDict::new();
 
@@ -108,10 +116,12 @@ pub(crate) fn write_term_to_heap(term: &Term, machine_st: &mut MachineState) ->
                     continue;
                 }
             },
-            &TermRef::AnonVar(Level::Root)
-          | &TermRef::Var(Level::Root, ..)
-          | &TermRef::Constant(Level::Root, ..) =>
+            &TermRef::AnonVar(Level::Root) | &TermRef::Constant(Level::Root, ..) =>
                 machine_st.heap.push(HeapCellValue::Addr(term.as_addr(h))),
+            &TermRef::Var(Level::Root, _, ref name) => {
+                max_var_length = std::cmp::max(max_var_length, name.len());                
+                machine_st.heap.push(HeapCellValue::Addr(term.as_addr(h)));
+            },
             &TermRef::AnonVar(_) => {
                 if let Some((arity, site_h)) = queue.pop_front() {
                     if arity > 1 {
@@ -134,6 +144,7 @@ pub(crate) fn write_term_to_heap(term: &Term, machine_st: &mut MachineState) ->
                     }
                 }
 
+                max_var_length = std::cmp::max(max_var_length, var.len());
                 continue;
             },
             _ => {}
@@ -142,5 +153,5 @@ pub(crate) fn write_term_to_heap(term: &Term, machine_st: &mut MachineState) ->
         modify_head_of_queue(machine_st, &mut queue, term, h);
     }
 
-    (h, var_dict)
+    TermWriteResult { heap_loc, var_dict, max_var_length }
 }