remove SCCCutPolicy panic, revise (;)/2 so that comma'ed cuts are handled properly (#361)

src/prolog/machine/code_repo.rs

@@ -60,7 +60,8 @@ impl CodeRepo {
             .unwrap_or((Predicate::new(), VecDeque::from(vec![])))
     }
 
-    pub(crate) fn add_in_situ_result(
+    pub(crate)
+    fn add_in_situ_result(
         &mut self,
         result: &CompiledResult,
         in_situ_code_dir: &mut InSituCodeDir,
@@ -100,16 +101,19 @@ impl CodeRepo {
     }
 
     #[inline]
-    pub(super) fn size_of_cached_query(&self) -> usize {
+    pub(super)
+    fn size_of_cached_query(&self) -> usize {
         self.cached_query.len()
     }
 
     #[inline]
-    pub(super) fn take_in_situ_code(&mut self) -> Code {
+    pub(super)
+    fn take_in_situ_code(&mut self) -> Code {
         mem::replace(&mut self.in_situ_code, Code::new())
     }
 
-    pub(super) fn lookup_instr<'a>(
+    pub(super)
+    fn lookup_instr<'a>(
         &'a self,
         last_call: bool,
         p: &CodePtr,

src/prolog/machine/system_calls.rs

@@ -2280,7 +2280,8 @@ impl MachineState {
                             }
                         }
                     }
-                    None => panic!("expected SCCCutPolicy trait object."),
+                    None => {
+                    }
                 };
 
                 self.fail = true;

src/prolog/machine/toplevel.rs

@@ -934,7 +934,7 @@ impl RelationWorker {
                 let mut term = *term;
 
                 if let Term::Clause(cell, name, terms, op_spec) = term {
-                    if name.as_str() == "," {
+                    if name.as_str() == "," && terms.len() == 2 {
                         let term = Term::Clause(cell, name, terms, op_spec);
                         let mut subterms = unfold_by_str(term, ",");