From d57a5922730b4a7a95776744dc0dcfdddcdf3036 Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Mon, 3 Aug 2020 19:29:53 -0600
Subject: [PATCH] unify '[]' with proper [] in atom_chars/2 (#569)

---
 Cargo.lock                  |  4 ++--
 Cargo.toml                  |  2 +-
 src/machine/system_calls.rs | 24 ++++++++++++++----------
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 531d0e50..526b9644 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -905,9 +905,9 @@ dependencies = [
 
 [[package]]
 name = "prolog_parser"
-version = "0.8.65"
+version = "0.8.66"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fdcfe8260335a150812e36b171ff985ce88f02de16c05f4a13fe4f10e8c247f8"
+checksum = "e35f5db0eb6725d00be12f3c9550de0dce0a43a1fa25a873f879613d63fcbbd5"
 dependencies = [
  "lexical",
  "num-rug-adapter",
diff --git a/Cargo.toml b/Cargo.toml
index c359e1ba..4b4bc1bf 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -32,7 +32,7 @@ libc = "0.2.62"
 nix = "0.15.0"
 num-rug-adapter = { optional = true, version = "0.1.3" }
 ordered-float = "0.5.0"
-prolog_parser = { version = "0.8.65", default-features = false }
+prolog_parser = { version = "0.8.66", default-features = false }
 ref_thread_local = "0.0.0"
 rug = { version = "1.4.0", optional = true }
 rustyline = "6.0.0"
diff --git a/src/machine/system_calls.rs b/src/machine/system_calls.rs
index 644f8296..ada49a0f 100644
--- a/src/machine/system_calls.rs
+++ b/src/machine/system_calls.rs
@@ -1029,20 +1029,24 @@ impl MachineState {
 
                         match iter.focus() {
                             Addr::EmptyList => {
-                                let chars = clause_name!(string, indices.atom_tbl);
-                                let atom  = self.heap.to_unifiable(
-                                    HeapCellValue::Atom(chars, None)
-                                );
+                                if &string == "[]" {
+                                    self.unify(addr, Addr::EmptyList);
+                                } else {
+                                    let chars = clause_name!(string, indices.atom_tbl);
+                                    let atom  = self.heap.to_unifiable(
+                                        HeapCellValue::Atom(chars, None)
+                                    );
 
-                                self.unify(addr, atom);
+                                    self.unify(addr, atom);
+                                }
                             }
                             focus => {
-                                let stub = MachineError::functor_stub(
-                                    clause_name!("atom_chars"),
-                                    2,
-                                );
-
                                 if let Addr::Lis(l) = focus {
+                                    let stub = MachineError::functor_stub(
+                                        clause_name!("atom_chars"),
+                                        2,
+                                    );
+
                                     let err = MachineError::type_error(
                                         self.heap.h(),
                                         ValidType::Character,
-- 
2.54.0