From b8400e0c92f0fb01cfdab5bf4e6bb48248ddf9a1 Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Sun, 3 May 2020 18:43:23 -0600
Subject: [PATCH] make term{_attributed_}variables/2 order {attributed}
 variables by left-to-right occurrence

---
 src/prolog/machine/attributed_variables.rs |  8 +++-----
 src/prolog/machine/system_calls.rs         | 10 +++-------
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/src/prolog/machine/attributed_variables.rs b/src/prolog/machine/attributed_variables.rs
index 6595ba53..b7e9ceee 100644
--- a/src/prolog/machine/attributed_variables.rs
+++ b/src/prolog/machine/attributed_variables.rs
@@ -1,8 +1,6 @@
 use crate::prolog::heap_iter::*;
 use crate::prolog::machine::*;
 
-use indexmap::IndexSet;
-
 use std::cmp::Ordering;
 use std::vec::IntoIter;
 
@@ -142,13 +140,13 @@ impl MachineState {
     }
 
     pub(super)
-    fn attr_vars_of_term(&self, addr: Addr) -> IndexSet<Addr> {
-        let mut seen_vars = IndexSet::new();
+    fn attr_vars_of_term(&self, addr: Addr) -> Vec<Addr> {
+        let mut seen_vars = vec![];
         let mut iter = self.acyclic_pre_order_iter(addr);
 
         while let Some(addr) = iter.next() {
             if let HeapCellValue::Addr(Addr::AttrVar(h)) = self.heap.index_addr(&addr).as_ref() {
-                seen_vars.insert(addr);
+                seen_vars.push(addr);
 
                 let mut l = h + 1;
                 let mut list_elements = vec![];
diff --git a/src/prolog/machine/system_calls.rs b/src/prolog/machine/system_calls.rs
index 74f82215..881789ea 100644
--- a/src/prolog/machine/system_calls.rs
+++ b/src/prolog/machine/system_calls.rs
@@ -20,8 +20,6 @@ use crate::prolog::rug::Integer;
 
 use crate::ref_thread_local::RefThreadLocal;
 
-use indexmap::IndexSet;
-
 use std::cmp;
 use std::convert::TryFrom;
 use std::io::{stdout, Read, Write};
@@ -3378,18 +3376,16 @@ impl MachineState {
             }
             &SystemClauseType::TermVariables => {
                 let a1 = self[temp_v!(1)];
-                let mut seen_vars = IndexSet::new();
+                let mut seen_vars = vec![];
 
                 for addr in self.acyclic_pre_order_iter(a1) {
                     if addr.is_ref() {
-                        seen_vars.insert(addr);
+                        seen_vars.push(addr);
                     }
                 }
 
                 let outcome = Addr::HeapCell(self.heap.to_list(seen_vars.into_iter()));
-
-                let a2 = self[temp_v!(2)];
-                self.unify(a2, outcome);
+                self.unify(self[temp_v!(2)], outcome);
             }
             &SystemClauseType::TruncateLiftedHeapTo => {
                 match self.store(self.deref(self[temp_v!(1)])) {
-- 
2.54.0