print lists as strings when possible (#295)

src/prolog/heap_print.rs

@@ -1024,31 +1024,7 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
         }
     }
 
-    fn print_string(
+    fn print_proper_string(&mut self, buf: String, max_depth: usize) {
-        &mut self,
-        iter: &mut HCPreOrderIterator,
-        mut max_depth: usize,
-        h: usize,
-        n: usize,
-    ) {
-        iter.stack().pop();
-        iter.stack().pop();
-
-        if self.check_max_depth(&mut max_depth) {
-            self.state_stack.push(TokenOrRedirect::Atom(clause_name!("...")));
-            return;
-        }
-
-        let mut heap_pstr_iter =
-            self.machine_st.heap_pstr_iter(Addr::PStrLocation(h, n));
-
-        let buf = heap_pstr_iter.to_string();
-        let end_addr = heap_pstr_iter.focus();
-
-        let at_cdr = self.at_cdr(",");
-
-        if !at_cdr && Addr::EmptyList == end_addr {
-            if !self.machine_st.flags.double_quotes.is_codes() {
         self.push_char('"');
 
         let buf =
@@ -1073,7 +1049,42 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
 
         self.append_str(&buf);
         self.push_char('"');
+    }
 
+    fn print_list_like(
+        &mut self,
+        iter: &mut HCPreOrderIterator,
+        addr: Addr,
+        mut max_depth: usize,
+    ) {
+        let a1 = iter.stack().pop();
+        let a2 = iter.stack().pop();
+
+        if self.check_max_depth(&mut max_depth) {
+            self.state_stack.push(TokenOrRedirect::Atom(clause_name!("...")));
+            return;
+        }
+
+        let mut heap_pstr_iter =
+            self.machine_st.heap_pstr_iter(addr);
+
+        let buf = heap_pstr_iter.to_string();
+
+        if buf.is_empty() {
+            iter.stack().push(a2.unwrap());
+            iter.stack().push(a1.unwrap());
+
+            self.push_list(iter, max_depth);
+            return;
+        }
+
+        let end_addr = heap_pstr_iter.focus();
+
+        let at_cdr = self.at_cdr(",");
+
+        if !at_cdr && Addr::EmptyList == end_addr {
+            if !self.machine_st.flags.double_quotes.is_codes() {
+                self.print_proper_string(buf, max_depth);
                 return;
             }
         }
@@ -1332,13 +1343,13 @@ impl<'a, Outputter: HCValueOutputter> HCPrinter<'a, Outputter> {
                 self.append_str(&format!("{}", u));
             }
             &HeapCellValue::Addr(Addr::PStrLocation(h, n)) => {
-                self.print_string(iter, max_depth, h, n);
+                self.print_list_like(iter, Addr::PStrLocation(h, n), max_depth);
             }
-            &HeapCellValue::Addr(Addr::Lis(_)) => {
+            &HeapCellValue::Addr(Addr::Lis(l)) => {
                 if self.ignore_ops {
                     self.format_struct(iter, max_depth, 2, clause_name!("."));
                 } else {
-                    self.push_list(iter, max_depth);
+                    self.print_list_like(iter, Addr::Lis(l), max_depth); //self.push_list(iter, max_depth);
                 }
             }
             &HeapCellValue::Addr(addr) => {