correct printing of lists when double_quotes is set to atom

src/prolog/heap_print.rs

@@ -339,8 +339,10 @@ impl<'a, Formatter: HCValueFormatter, Outputter: HCValueOutputter>
                     }
                     // self.expand_char_list(s);
                 } else { // for now, == DoubleQuotes::Atom
+                    let borrowed_str = s.borrow();
+                    
                     self.outputter.append("\"");
-                    self.outputter.append(s.borrow().as_str());
+                    self.outputter.append(&borrowed_str[s.cursor() ..]);
                     self.outputter.append("\"");
                 },            
             Constant::Usize(i) =>

src/prolog/read.rs

@@ -49,7 +49,7 @@ impl<'a> Reader<'a> {
             };
         }
     }
-
+    
     fn push_stub_addr(&mut self) {
         let h = self.machine_st.heap.h;
         self.machine_st.heap.push(HeapCellValue::Addr(Addr::HeapCell(h)));

src/prolog/string_list.rs

@@ -64,6 +64,11 @@ impl StringList {
         }
     }
 
+    #[inline]
+    pub fn cursor(&self) -> usize {
+        self.cursor
+    }        
+    
     #[inline]
     pub fn head(&self) -> Option<char> {
         self.borrow()[self.cursor ..].chars().next()

src/tests.rs

@@ -1786,4 +1786,9 @@ fn test_queries_on_string_lists()
     assert_prolog_success!(&mut wam, "?- matcher(X, Y).",
                           [["X = [a, b, c | _1]", "Y = _1"]]);
     assert_prolog_failure!(&mut wam, "?- matcher(\"abcdef\", Y).");
+
+    submit(&mut wam, "?- set_prolog_flag(double_quotes, chars).");
+    
+    assert_prolog_success!(&mut wam, "?- X = \"abc\", X = ['a' | Y], set_prolog_flag(double_quotes, atom).",
+                           [["X = \"abc\"", "Y = \"bc\""]]);
 }