add some prolog flags, tabled strings

src/prolog/machine/machine_state.rs

@@ -264,6 +264,28 @@ pub(super) enum MachineMode {
     Write
 }
 
+#[derive(Clone, Copy)]
+pub(super) enum DoubleQuotes {
+    Atom, Chars, // Codes
+}
+
+impl Default for DoubleQuotes {
+    fn default() -> Self {
+        DoubleQuotes::Chars
+    }
+}
+
+#[derive(Clone, Copy)]
+pub(super) struct MachineFlags {
+    pub(super) double_quotes: DoubleQuotes
+}
+
+impl Default for MachineFlags {
+    fn default() -> Self {
+        MachineFlags { double_quotes: DoubleQuotes::default() }
+    }
+}
+
 pub struct MachineState {
     pub(crate) atom_tbl: TabledData<Atom>,
     pub(super) s: usize,
@@ -285,7 +307,8 @@ pub struct MachineState {
     pub(super) block: usize, // an offset into the OR stack.
     pub(super) ball: Ball,
     pub(super) interms: Vec<Number>, // intermediate numbers.
-    pub(super) last_call: bool
+    pub(super) last_call: bool,
+    pub(super) flags: MachineFlags
 }
 
 fn call_at_index(machine_st: &mut MachineState, module_name: ClauseName, arity: usize, idx: usize)

src/prolog/machine/machine_state_impl.rs

@@ -50,7 +50,8 @@ impl MachineState {
             block: 0,
             ball: Ball::new(),
             interms: vec![Number::default(); 256],
-            last_call: false
+            last_call: false,
+            flags: MachineFlags::default()
         }
     }
 

src/prolog/machine/system_calls.rs

@@ -195,6 +195,16 @@ impl MachineState {
                     _ => self.fail = true
                 };
             },
+            &SystemClauseType::GetDoubleQuotes => {
+                let a1 = self[temp_v!(1)].clone();
+                
+                match self.flags.double_quotes {
+                    DoubleQuotes::Chars =>
+                        self.unify(a1, Addr::Con(atom!("chars"))),
+                    DoubleQuotes::Atom =>
+                        self.unify(a1, Addr::Con(atom!("atom")))
+                }
+            },
             &SystemClauseType::GetSCCCleaner => {
                 let dest = self[temp_v!(1)].clone();
 
@@ -330,6 +340,14 @@ impl MachineState {
             },
             &SystemClauseType::SetCutPointByDefault(r) =>
                 deref_cut(self, r),
+            &SystemClauseType::SetDoubleQuotes =>
+                match self[temp_v!(1)].clone() {
+                    Addr::Con(Constant::Atom(ref atom)) if atom.as_str() == "chars" =>
+                        self.flags.double_quotes = DoubleQuotes::Chars,
+                    Addr::Con(Constant::Atom(ref atom)) if atom.as_str() == "atom" =>
+                        self.flags.double_quotes = DoubleQuotes::Atom,
+                    _ => self.fail = true
+                },
             &SystemClauseType::InferenceLevel => {
                 let a1 = self[temp_v!(1)].clone();
                 let a2 = self.store(self.deref(self[temp_v!(2)].clone()));