accomodate \0\ in partial strings, print null as \0\ (#267, #526), update prolog parser, version bump

src/prolog/machine/heap.rs

@@ -189,6 +189,10 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
     #[inline]
     pub(crate)
     fn put_complete_string(&mut self, s: &str) -> Addr {
+        if s.is_empty() {
+            return Addr::EmptyList;
+        }
+
         let addr = self.allocate_pstr(s);
         self.pop();
 
@@ -316,20 +320,7 @@ impl<T: RawBlockTraits> HeapTemplate<T> {
     pub(crate)
     fn allocate_pstr(&mut self, src: &str) -> Addr {
         self.write_pstr(src)
-            .unwrap_or_else(|| {
-                let h = self.h();
-
-                self.push(HeapCellValue::PartialString(
-                    PartialString::empty(),
-                    true,
-                ));
-
-                self.push(HeapCellValue::Addr(
-                    Addr::HeapCell(h + 1)
-                ));
-
-                Addr::PStrLocation(h, 0)
-            })
+            .unwrap_or_else(|| Addr::EmptyList)
     }
 
     #[inline]

src/prolog/machine/machine_state_impl.rs

@@ -1492,9 +1492,13 @@ impl MachineState {
             &QueryInstruction::PutPartialString(_, ref string, reg, has_tail) => {
                 let pstr_addr =
                     if has_tail {
-                        let pstr_addr = self.heap.allocate_pstr(&string);
-                        self.heap.pop(); // the tail will be added by the next instruction.
-                        pstr_addr
+                        if !string.is_empty() {
+                            let pstr_addr = self.heap.allocate_pstr(&string);
+                            self.heap.pop(); // the tail will be added by the next instruction.
+                            pstr_addr
+                        } else {
+                            Addr::EmptyList
+                        }
                     } else {
                         self.heap.put_complete_string(&string)
                     };

src/prolog/machine/partial_string.rs

@@ -37,8 +37,8 @@ fn scan_for_terminator<Iter: Iterator<Item = char>>(iter: Iter) -> usize {
     let mut terminator_idx = 0;
 
     for c in iter {
-        if c == '\u{0}' {
-            break;
+        if c == '\u{0}' && terminator_idx != 0 {
+            return terminator_idx;
         }
 
         terminator_idx += c.len_utf8();
@@ -98,37 +98,9 @@ impl PartialString {
         }
     }
 
-    #[inline]
-    pub(super)
-    fn empty() -> Self {
-        let mut pstr = PartialString {
-            buf: ptr::null(),
-            len: 0,
-            _marker: PhantomData,
-        };
-
-        unsafe {
-            let layout = alloc::Layout::from_size_align_unchecked(
-                '\u{0}'.len_utf8(),
-                mem::align_of::<u8>(),
-            );
-
-            pstr.buf = alloc::alloc(layout) as *const _;
-            pstr.len = '\u{0}'.len_utf8();
-
-            pstr.write_terminator_at(0);
-        }
-
-        pstr
-    }
-
     unsafe fn append_chars(mut self, src: &str) -> Option<(Self, &str)> {
         let terminator_idx = scan_for_terminator(src.chars());
 
-        if terminator_idx == 0 {
-            return None;
-        }
-
         let layout = alloc::Layout::from_size_align_unchecked(
             terminator_idx + '\u{0}'.len_utf8(),
             mem::align_of::<u8>(),
@@ -145,8 +117,8 @@ impl PartialString {
 
         self.write_terminator_at(terminator_idx);
 
-        Some(if terminator_idx != src.len() {
-            (self, &src[terminator_idx + '\u{0}'.len_utf8() ..])
+        Some(if terminator_idx != src.as_bytes().len() {
+            (self, &src[terminator_idx ..])
         } else {
             (self, "")
         })
@@ -211,9 +183,7 @@ impl PartialString {
 
     #[inline]
     pub fn at_end(&self, end_n: usize) -> bool {
-        unsafe {
-            ptr::read((self.buf as usize + end_n) as *const u8) == 0u8
-        }
+        end_n + 1 == self.len
     }
 
     #[inline]

src/prolog/machine/system_calls.rs

@@ -1110,6 +1110,11 @@ impl MachineState {
 
                 let h = self.heap.h();
 
+                if atom.as_str().is_empty() {
+                    self.fail = true;
+                    return Ok(());
+                }
+
                 let pstr = self.heap.allocate_pstr(atom.as_str());
                 let pstr_tail = self.heap[h + 1].as_addr(h + 1);