distinguish eq from structural_eq on strings

src/prolog/machine/machine_state.rs

@@ -6,7 +6,6 @@ use prolog::machine::machine_errors::*;
 use prolog::num::{BigInt, BigUint, Zero, One};
 use prolog::or_stack::*;
 use prolog::read::*;
-use prolog::string_list::*;
 use prolog::tabled_rc::*;
 
 use downcast::Any;
@@ -299,7 +298,6 @@ impl Default for MachineFlags {
 
 pub struct MachineState {
     pub(crate) atom_tbl: TabledData<Atom>,
-    pub(crate) string_tbl: TabledData<StringListWrapper>,
     pub(super) s: usize,
     pub(super) p: CodePtr,
     pub(super) b: usize,
@@ -626,15 +624,7 @@ pub(crate) trait CallPolicy: Any {
                 return_from_clause!(machine_st.last_call, machine_st)
             },
             &BuiltInClauseType::Eq => {
-                let a1 = machine_st[temp_v!(1)].clone();
-                let a2 = machine_st[temp_v!(2)].clone();
-
-                machine_st.fail = if let Ordering::Equal = machine_st.compare_term_test(&a1, &a2) {
-                    false
-                } else {
-                    true
-                };
-
+                machine_st.fail = machine_st.eq_test();
                 return_from_clause!(machine_st.last_call, machine_st)
             },
             &BuiltInClauseType::Ground => {