Merge branch 'master' of http://github.com/mthom/rusty-wam into develop

src/prolog/ast.rs

@@ -537,7 +537,7 @@ impl fmt::Display for Constant {
             &Constant::Atom(ref atom) =>
                 write!(f, "{}", atom),
             &Constant::Char(c) =>
-                write!(f, "{}", c as u8),
+                write!(f, "'{}'", c as u8),
             &Constant::EmptyList =>
                 write!(f, "[]"),
             &Constant::Number(ref n) =>
@@ -1360,13 +1360,6 @@ impl Addr {
             _ => true
         }
     }
-
-    pub fn is_empty_list(&self) -> bool {
-        match self {
-            &Addr::Con(Constant::EmptyList) => true,
-            _ => false
-        }
-    }
 }
 
 impl From<Ref> for Addr {

src/prolog/builtins.rs

@@ -644,6 +644,7 @@ fn get_builtins() -> Code {
          keysort_execute!(), // keysort/2, 484.
          acyclic_term_execute!(), // acyclic_term/1, 485.
          cyclic_term_execute!(), // cyclic_term/1, 486.
+         skip_max_list_execute!() // '$skip_max_list', 487.
     ]
 }
 
@@ -763,7 +764,8 @@ pub fn build_code_and_op_dirs() -> (CodeDir, OpDir)
     code_dir.insert((clause_name!("keysort"), 2), CodeIndex::from((484, builtin.clone())));
     code_dir.insert((clause_name!("acyclic_term"), 1), CodeIndex::from((485, builtin.clone())));
     code_dir.insert((clause_name!("cyclic_term"), 1), CodeIndex::from((486, builtin.clone())));
-
+    code_dir.insert((clause_name!("$skip_max_list"), 4), CodeIndex::from((487, builtin.clone())));
+    
     (code_dir, op_dir)
 }
 
@@ -826,7 +828,8 @@ pub fn builtin_module() -> Module
                                             (clause_name!("sort"), 2),
                                             (clause_name!("keysort"), 2),
                                             (clause_name!("acyclic_term"), 1),
-                                            (clause_name!("cyclic_term"), 1)]);
+                                            (clause_name!("cyclic_term"), 1),
+                                            (clause_name!("$skip_max_list"), 4)]);
 
     for arity in 0 .. 63 {
         module_decl.exports.push((clause_name!("call"), arity));

src/prolog/machine/machine_state_impl.rs

@@ -29,9 +29,10 @@ macro_rules! try_or_fail {
 // used by '$skip_max_list'.
 enum CycleSearchResult {
     EmptyList,
-    NotList,
+    NotList,    
-    PartialOrProperList(usize, usize), // returns the list length (up to max), and an offset into the heap.
+    PartialList(usize, usize), // the list length (up to max), and an offset into the heap.
-    UntouchedList(usize) // return the offset of an uniterated Addr::Lis(offset).
+    ProperList(usize), // the list length.
+    UntouchedList(usize) // the address of an uniterated Addr::Lis(address).
 }
 
 impl MachineState {
@@ -1686,8 +1687,7 @@ impl MachineState {
 
         // detect cycles.
         match self.detect_cycles(usize::max_value(), a1.clone()) {
-            CycleSearchResult::PartialOrProperList(_, h)
+            CycleSearchResult::ProperList(_) => {},
-                if self.store(self.deref(self.heap[h].as_addr(h))).is_empty_list() => {},
             _ => return Err(functor!("type_error", 2, [heap_atom!("list"), HeapCellValue::Addr(a1)]))
         };
 
@@ -1752,7 +1752,7 @@ impl MachineState {
 
         loop {
             if steps == max_steps {
-                return CycleSearchResult::PartialOrProperList(steps, hare);
+                return CycleSearchResult::PartialList(steps, hare);
             }
 
             match self.heap[hare].clone() {
@@ -1768,13 +1768,8 @@ impl MachineState {
                     }
                 },
                 HeapCellValue::Addr(Addr::Con(Constant::EmptyList)) =>
-                    return CycleSearchResult::PartialOrProperList(steps, hare),
+                    return CycleSearchResult::ProperList(steps),
-                HeapCellValue::Addr(Addr::HeapCell(hc)) if hc == hare =>
+                _ => return CycleSearchResult::PartialList(steps, hare)
-                    return CycleSearchResult::PartialOrProperList(steps, hare),
-                HeapCellValue::Addr(ref sc @ Addr::StackCell(..))
-                    if *sc == self.store(self.deref(sc.clone())) =>
-                      return CycleSearchResult::PartialOrProperList(steps, hare),
-                _ => return CycleSearchResult::NotList
             }
         }
     }
@@ -1788,17 +1783,7 @@ impl MachineState {
             self.unify(addr, xs);
         }
     }
-
+    
-/*
-  '$skip_max_list'(N, Max, Xs0, Xs):
-  valid modes: Max is always +Max (a non-negative integer), Xs, Xs0 and N are all ?_.
-
-  Modes        | Conditions for success
-  ======================================================================================
-      ?N, -Xs0 : N = 0, Xs = Xs0.
-      ?N, +Xs0 : Xs0 is a proper or partial list, Xs0 = [X1, X2, ..., XN | Xs], N = Max,
-                 if |Xs0| >= Max, or, Xs = [] and N = |Xs0|.
-*/
     pub(super) fn skip_max_list(&mut self) {
         let max = self.store(self.deref(self[temp_v!(2)].clone()));
 
@@ -1822,10 +1807,14 @@ impl MachineState {
                                     self.finalize_skip_max_list(0, Addr::Lis(l)),
                                 CycleSearchResult::EmptyList =>
                                     self.finalize_skip_max_list(0, Addr::Con(Constant::EmptyList)),
-                                CycleSearchResult::PartialOrProperList(n, hc) =>
+                                CycleSearchResult::PartialList(n, hc) =>
                                     self.finalize_skip_max_list(n, Addr::HeapCell(hc)),
-                                CycleSearchResult::NotList =>
+                                CycleSearchResult::ProperList(n) =>
-                                    self.fail = true
+                                    self.finalize_skip_max_list(n, Addr::Con(Constant::EmptyList)),
+                                CycleSearchResult::NotList => {
+                                    let xs0 = self[temp_v!(3)].clone();
+                                    self.finalize_skip_max_list(0, xs0);
+                                }
                             }
                         }
                     }

src/prolog/macros.rs

@@ -763,6 +763,12 @@ macro_rules! cyclic_term_execute {
     )
 }
 
+macro_rules! skip_max_list_execute {
+    () => (
+        Line::Control(ControlInstruction::CallClause(ClauseType::SkipMaxList, 4, 0, true))
+    )
+}
+
 macro_rules! return_from_clause {
     ($lco:expr, $machine_st:expr) => {{
         if $lco {

src/tests.rs

@@ -1644,4 +1644,8 @@ fn test_queries_on_skip_max_list() {
     assert_prolog_failure!(&mut wam, "?- Xs = [a,b|Xs], '$skip_max_list'(3, 5, X, Xs0).");
     assert_prolog_failure!(&mut wam, "?- X = [a,b|Y], Y = [c,d|X], '$skip_max_list'(4, 5, X, Xs0).");
     assert_prolog_failure!(&mut wam, "?- X = [a,b|Y], Y = [c,d|X], '$skip_max_list'(4, 3, X, Xs0).");
+
+    // tests on non lists.
+    assert_prolog_success!(&mut wam, "?- '$skip_max_list'(N, 9, non_list, Xs).",
+                           [["Xs = non_list", "N = 0"]]);
 }