Fix errors, move prolog_parser

crates/prolog_parser/src/put_back_n.rs

@@ -0,0 +1,71 @@
+use std::iter::Peekable;
+
+#[derive(Debug, Clone)]
+pub struct PutBackN<I: Iterator> {
+    top: Vec<I::Item>,
+    iter: Peekable<I>,
+}
+
+pub fn put_back_n<I>(iterable: I) -> PutBackN<I::IntoIter>
+    where I: IntoIterator
+{
+    PutBackN {
+        top: Vec::new(),
+        iter: iterable.into_iter().peekable(),
+    }
+}
+
+impl<I: Iterator> PutBackN<I> {
+    #[inline]
+    pub(crate)
+    fn put_back(&mut self, item: I::Item) {
+        self.top.push(item);
+    }
+
+    #[inline]
+    pub fn take_buf(&mut self) -> Vec<I::Item> {
+        std::mem::replace(&mut self.top, vec![])
+    }
+
+    #[inline]
+    pub(crate)
+    fn peek(&mut self) -> Option<&I::Item> {
+        if self.top.is_empty() {
+            /* This is a kludge for Ctrl-D not being
+             * handled properly if self.iter().peek() isn't called
+             * first. */
+            match self.iter.peek() {
+                Some(_) => {
+                    self.iter.next().and_then(move |item| {
+                        self.top.push(item);
+                        self.top.last()
+                    })
+                }
+                None => {
+                    None
+                }
+            }
+        } else {
+            self.top.last()
+        }
+    }
+
+    #[inline]
+    pub(crate)
+    fn put_back_all<DEI: DoubleEndedIterator<Item = I::Item>>(&mut self, iter: DEI) {
+        self.top.extend(iter.rev());
+    }
+}
+
+impl<I: Iterator> Iterator for PutBackN<I> {
+    type Item = I::Item;
+
+    #[inline]
+    fn next(&mut self) -> Option<I::Item> {
+        if self.top.is_empty() {
+            self.iter.next()
+        } else {
+            self.top.pop()
+        }
+    }
+}