From 775bd3a08bcc42acaf6fcc790a9cd444a41469ed Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Fri, 25 Feb 2022 23:01:08 -0700
Subject: [PATCH] unify '' to [] in unify_complete_string (#1292, #1288)

---
 src/machine/machine_state_impl.rs | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/machine/machine_state_impl.rs b/src/machine/machine_state_impl.rs
index 85fac031..5003d14a 100644
--- a/src/machine/machine_state_impl.rs
+++ b/src/machine/machine_state_impl.rs
@@ -333,11 +333,20 @@ impl MachineState {
 
     pub fn unify_complete_string(&mut self, atom: Atom, value: HeapCellValue) {
         if let Some(r) = value.as_var() {
-            self.bind(r, atom_as_cstr_cell!(atom));
+            if atom == atom!("") {
+                self.bind(r, atom_as_cell!(atom!("[]")));
+            } else {
+                self.bind(r, atom_as_cstr_cell!(atom));
+            }
+
             return;
         }
 
         read_heap_cell!(value,
+            (HeapCellValueTag::Atom, (cstr_atom, arity)) if atom == atom!("") => {
+                debug_assert_eq!(arity, 0);
+                self.fail = cstr_atom != atom!("[]");
+            }
             (HeapCellValueTag::CStr, cstr_atom) => {
                 self.fail = atom != cstr_atom;
             }
@@ -713,7 +722,6 @@ impl MachineState {
 
     pub fn unify(&mut self) {
         let mut tabu_list: IndexSet<(usize, usize)> = IndexSet::new();
-        // self.fail = false;
 
         while !(self.pdl.is_empty() || self.fail) {
             let s1 = self.pdl.pop().unwrap();
-- 
2.54.0