Revert "remove Term"

This reverts commit 3b5879841aedecba5057c70c71da0ba23e5cd84a.

src/machine/machine_indices.rs

@@ -21,8 +21,6 @@ use std::collections::BTreeSet;
 use std::ops::{Deref, DerefMut};
 
 use crate::types::*;
-// #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-// pub(crate) struct OrderedOpDirKey(pub(crate) Atom, pub(crate) Fixity);
 
 // 7.2
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
@@ -223,6 +221,30 @@ impl CodeIndex {
     */
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum VarKey {
+    AnonVar(usize),
+    VarPtr(VarPtr),
+}
+
+impl VarKey {
+    #[allow(clippy::inherent_to_string)]
+    #[inline]
+    pub(crate) fn to_string(&self) -> String {
+        match self {
+            VarKey::AnonVar(h) => format!("_{}", h),
+            VarKey::VarPtr(var) => var.borrow().to_string(),
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn is_anon(&self) -> bool {
+        matches!(self, VarKey::AnonVar(_))
+    }
+}
+
+pub(crate) type HeapVarDict = IndexMap<VarKey, HeapCellValue, FxBuildHasher>;
+
 pub(crate) type GlobalVarDir = IndexMap<Atom, (Ball, Option<HeapCellValue>), FxBuildHasher>;
 
 pub(crate) type StreamAliasDir = IndexMap<Atom, Stream, FxBuildHasher>;
@@ -279,9 +301,11 @@ impl IndexStore {
             _ => self
                 .get_meta_predicate_spec(key.0, key.1, &compilation_target)
                 .map(|meta_specs| {
-                    meta_specs.iter().find(|meta_spec| match meta_spec {
-                        MetaSpec::Colon | MetaSpec::RequiresExpansionWithArgument(_) => true,
-                        _ => false,
+                    meta_specs.iter().find(|meta_spec| {
+                        matches!(
+                            meta_spec,
+                            MetaSpec::Colon | MetaSpec::RequiresExpansionWithArgument(_)
+                        )
                     })
                 })
                 .map(|meta_spec_opt| meta_spec_opt.is_some())