add term_attributed_variables/2 (#422)

src/prolog/machine/attributed_variables.rs

@@ -1,5 +1,8 @@
+use crate::prolog::heap_iter::*;
 use crate::prolog::machine::*;
 
+use indexmap::IndexSet;
+
 use std::cmp::Ordering;
 use std::vec::IntoIter;
 
@@ -137,4 +140,30 @@ impl MachineState {
         self.b0 = self.b;
         self.p = CodePtr::Local(LocalCodePtr::DirEntry(p));
     }
+
+    pub(super)
+    fn attr_vars_of_term(&self, addr: Addr) -> IndexSet<Addr> {
+        let mut seen_vars = IndexSet::new();
+        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);
+
+                let mut l = h + 1;
+                let mut list_elements = vec![];
+
+                while let Addr::Lis(elem) = self.store(self.deref(Addr::HeapCell(l))) {
+                    list_elements.push(self.heap[elem].as_addr(elem));
+                    l = elem + 1;
+                }
+
+                for element in list_elements.into_iter().rev() {
+                    iter.stack().push(element);
+                }
+            }
+        }
+
+        seen_vars
+    }
 }

src/prolog/machine/system_calls.rs

@@ -4,11 +4,11 @@ use prolog_parser::tabled_rc::*;
 
 use crate::prolog::clause_types::*;
 use crate::prolog::forms::*;
+use crate::prolog::heap_print::*;
 use crate::prolog::instructions::*;
 use crate::prolog::machine::code_repo::CodeRepo;
 use crate::prolog::machine::copier::*;
 use crate::prolog::machine::code_walker::*;
-use crate::prolog::heap_print::*;
 use crate::prolog::machine::machine_errors::*;
 use crate::prolog::machine::machine_indices::*;
 use crate::prolog::machine::machine_state::*;
@@ -3368,6 +3368,12 @@ impl MachineState {
             }
             &SystemClauseType::Succeed => {
             }
+            &SystemClauseType::TermAttributedVariables => {
+                let seen_vars = self.attr_vars_of_term(self[temp_v!(1)]);
+                let outcome = Addr::HeapCell(self.heap.to_list(seen_vars.into_iter()));
+
+                self.unify(self[temp_v!(2)], outcome);
+            }
             &SystemClauseType::TermVariables => {
                 let a1 = self[temp_v!(1)];
                 let mut seen_vars = IndexSet::new();