diff --git a/day7.chpl b/day7.chpl
index e02a08f..11da9e0 100644
--- a/day7.chpl
+++ b/day7.chpl
@@ -1,17 +1,53 @@
+// Advent of Code 2022, Day 7: Traversing Directories
+// authors: ["Daniel Fedorin"]
+// summary: "A solution to day seven of AoC 2022, introducing classes and memory management."
+// tags: ["Advent of Code 2022"]
+// date: 2022-12-07
+
+/*
+  Welcome to day 7 of Chapel's Advent of Code 2022 series. We're over halway
+  through the twelve days of Chapel AoC! In case you haven't been following
+  the series, check out the introductory [Advent of Code 2022: Twelve
+  Days of Chapel](../aoc2022-day00-intro/) article for more context.
+ */
+
+/*
+  ### The Task at Hand and My Approach
+
+  In today's puzzle, we are given a list of terminal-like commands (
+  [`ls`](https://man7.org/linux/man-pages/man1/ls.1.html) and [`cd`](https://man7.org/linux/man-pages/man1/cd.1p.html)
+  ), as well as output corresponding to running these commands. The commands
+  explore a fictional file system, which can have files (objects with size)
+  as well as directories that group files and other (sub-)directories. The
+  problem then asks to compute the sizes of each folder, and to total up the
+  sizes of all folders that are smaller than a particular threshold.
+
+  The tree-like nature of the file system does not make it amenable to
+  representations based on arrays, lists, and maps alone. The trouble with
+  these data types is that they're flat. Our input could -- and will -- have arbitrary
+  levels of nested directories. However, arrays, lists, and maps cannot have
+  such arbitrary nesting -- we'd need something like a list of lists of lists...
+  We could, of course, use the `map` and `list` data types to represent the
+  file system with some sort of [adjacency list](https://en.wikipedia.org/wiki/Adjacency_list).
+  However, such an implementation would be somewhat clunky and hard to use.
+
+  Instead, we'll use a different tool from the repertoire of Chapel language
+  features, one we haven't seen so far: classes. Much like in most languages,
+  classes are a way to group together related pieces of data. up until now,
+  we've used tuples for this purpose.
+
+*/
+
 use IO, Map, List;
 
 class TreeNode {
   var name: string;
-  var parent: borrowed TreeNode?;
 
   var files = new map(string, int);
   var dirs = new list(owned TreeNode);
 
-  var size = -1;
-
-  proc init(name: string, parent: borrowed TreeNode?) {
+  proc init(name: string) {
     this.name = name;
-    this.parent = parent;
   }
 
   /*
@@ -32,43 +68,43 @@ class TreeNode {
 
   */
 
-  iter these(): (string, int) {
+  iter dirSizes(ref parentSize = 0): (string, int) {
     var size = + reduce files.values();
     for dir in dirs {
       // Yield directory sizes from the dir.
-      for subSize in dir.these() do yield subSize;
-      // Count its size for our size.
-      size += dir.size;
+      for subSize in dir.dirSizes(size) do yield subSize;
     }
     yield (name, size);
-    this.size = size;
+    parentSize += size;
   }
-}
 
-var rootFolder: owned TreeNode = new owned TreeNode("", nil);
-var currentFolder: borrowed TreeNode = rootFolder.borrow();
+  proc type fromInput(name: string, readFrom): owned TreeNode {
+    var line: string;
+    var newDir = new TreeNode(name);
 
-for line in stdin.lines() {
-  const strippedLine = line.strip();
-  if strippedLine == "$ cd .." {
-    if const parent = currentFolder.parent then
-      currentFolder = parent;
-  } else if strippedLine.startsWith("$ cd ") {
-    const dirName = strippedLine["$ cd ".size..];
-    var newFolder = new owned TreeNode(dirName, currentFolder);
-    currentFolder.dirs.append(newFolder);
-    currentFolder = currentFolder.dirs.last().borrow();
-  } else if !strippedLine.startsWith("$ ls") {
-    const (sizeOrDir, _, name) = strippedLine.partition(" ");
-    if sizeOrDir == "dir" {
-      // Ignore directories, we'll CD into them.
-    } else {
-      currentFolder.files[name] = sizeOrDir : int;
+    while readFrom.readLine(line, stripNewline = true) {
+      if line == "$ cd .." {
+        break;
+      } else if line.startsWith("$ cd ") {
+        const dirName = line["$ cd ".size..];
+        newDir.dirs.append(TreeNode.fromInput(dirName, readFrom));
+      } else if !line.startsWith("$ ls") {
+        const (sizeOrDir, _, name) = line.partition(" ");
+        if sizeOrDir == "dir" {
+          // Ignore directories, we'll `cd` into them.
+        } else {
+          newDir.files[name] = sizeOrDir : int;
+        }
+      }
     }
+    return newDir;
   }
 }
 
-writeln(+ reduce [(_, size) in rootFolder] if size < 100000 then size);
+var rootFolder = TreeNode.fromInput("", stdin);
 
-const toDelete = rootFolder.size - 40000000;
-writeln(min reduce [(_, size) in rootFolder] if size >= toDelete then size);
+var rootSize = 0;
+writeln(+ reduce [(_, size) in rootFolder.dirSizes(rootSize)] if size < 100000 then size);
+
+const toDelete = rootSize - 40000000;
+writeln(min reduce [(_, size) in rootFolder.dirSizes()] if size >= toDelete then size);