transition to prolog

src/prolog/and_stack.rs

@@ -0,0 +1,80 @@
+use prolog::ast::*;
+
+use std::ops::{Index, IndexMut};
+use std::vec::Vec;
+
+pub struct Frame {
+    pub global_index: usize,
+    pub e: usize,
+    pub cp: CodePtr,
+    perms: Vec<Addr>
+}
+
+impl Frame {
+    fn new(global_index: usize, e: usize, cp: CodePtr, n: usize) -> Self {
+        Frame {
+            global_index: global_index,
+            e: e,
+            cp: cp,
+            perms: vec![Addr::HeapCell(0); n]
+        }
+    }
+}
+
+pub struct AndStack(Vec<Frame>);
+
+impl AndStack {
+    pub fn new() -> Self {
+        AndStack(Vec::new())
+    }
+
+    pub fn push(&mut self, global_index: usize, e: usize, cp: CodePtr, n: usize) {
+        self.0.push(Frame::new(global_index, e, cp, n));
+    }
+
+    pub fn top(&self) -> Option<&Frame> {
+        self.0.last()
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn clear(&mut self) {
+        self.0.clear()
+    }
+
+    // drop the last n frames.
+    pub fn drop_frames(&mut self, n: usize) {
+        let len = self.0.len();
+        self.0.truncate(len - n);
+    }
+}
+
+impl Index<usize> for AndStack {
+    type Output = Frame;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        self.0.index(index)
+    }
+}
+
+impl IndexMut<usize> for AndStack {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        self.0.index_mut(index)
+    }
+}
+
+impl Index<usize> for Frame {
+    type Output = Addr;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        self.perms.index(index - 1)
+    }
+}
+
+impl IndexMut<usize> for Frame {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        self.perms.index_mut(index - 1)
+    }
+}