finished resolver (chapter 11) and started classes (chapter 12)

frontend/src/lexer/code_pos.rs

@@ -0,0 +1,23 @@
+#[derive(Copy, Clone)]
+pub struct CodePos {
+    pub line: u32,
+    pub col: u32,
+}
+
+impl Default for CodePos {
+    fn default() -> Self {
+        Self { line: 1, col: 0 }
+    }
+}
+
+impl std::fmt::Display for CodePos {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "line {}, col {}", self.line, self.col)
+    }
+}
+
+impl std::fmt::Debug for CodePos {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}:{}", self.line, self.col)
+    }
+}