separate out the line/column counting from character iteration

src/iterator.rs

@@ -0,0 +1,46 @@
+use std::iter::Peekable;
+use std::io;
+
+pub struct LineColIterator<Iter: Iterator<Item=io::Result<u8>>> {
+    rdr: Peekable<Iter>,
+    line: usize,
+    col: usize,
+}
+
+impl<Iter: Iterator<Item=io::Result<u8>>> LineColIterator<Iter> {
+    pub fn new(iter: Iter) -> LineColIterator<Iter> {
+        LineColIterator {
+            line: 1,
+            col: 0,
+            rdr: iter.peekable(),
+        }
+    }
+    fn peek(&mut self) -> Option<u8> {
+        match self.rdr.peek() {
+            None => None,
+            Some(&Ok(c)) => Some(c),
+            Some(&Err(_)) => None,
+        }
+    }
+    pub fn line(&self) -> usize { self.line }
+    pub fn col(&self) -> usize { self.col }
+}
+
+impl<Iter: Iterator<Item=io::Result<u8>>> Iterator for LineColIterator<Iter> {
+    type Item = io::Result<u8>;
+    fn next(&mut self) -> Option<io::Result<u8>> {
+        match self.rdr.next() {
+            None => None,
+            Some(Ok(b'\n')) => {
+                self.line += 1;
+                self.col = 0;
+                Some(Ok(b'\n'))
+            },
+            Some(Ok(c)) => {
+                self.col += 1;
+                Some(Ok(c))
+            },
+            Some(Err(e)) => Some(Err(e)),
+        }
+    }
+}