Make L5 more natural

src/levels/l05_dict_list.rs

@@ -23,13 +23,36 @@ const ITEMS: &[&str] = &[
 
 #[derive(Serialize)]
 struct DescCtx {
-    chambers: Vec<ChamberDesc>,
+    sentences: Vec<String>,
 }
 
-#[derive(Serialize)]
-struct ChamberDesc {
-    name: String,
-    items: Vec<String>,
+/// Pick "a" or "an" based on the first letter — keeps the prose reading
+/// naturally without giving away that chamber names are YAML keys.
+fn article(word: &str) -> &'static str {
+    let first = word.chars().next().map(|c| c.to_ascii_lowercase());
+    if matches!(first, Some('a') | Some('e') | Some('i') | Some('o') | Some('u')) {
+        "an"
+    } else {
+        "a"
+    }
+}
+
+/// Join the item list as English: `a sword`, `a sword and a shield`,
+/// `a sword, a shield, and a potion` (Oxford comma for 3+).
+fn join_items(items: &[&str]) -> String {
+    let parts: Vec<String> = items
+        .iter()
+        .map(|i| format!("{} {}", article(i), i))
+        .collect();
+    match parts.as_slice() {
+        [] => String::new(),
+        [one] => one.clone(),
+        [a, b] => format!("{a} and {b}"),
+        rest => {
+            let (last, head) = rest.split_last().unwrap();
+            format!("{}, and {}", head.join(", "), last)
+        }
+    }
 }
 
 impl Level for DictList {
@@ -48,7 +71,7 @@ impl Level for DictList {
             CHAMBERS.choose_multiple(&mut rng, n).copied().collect();
 
         let mut inner = Mapping::new();
-        let mut desc_chambers = Vec::new();
+        let mut sentences = Vec::new();
         for name in &chamber_names {
             let item_n = rng.gen_range(2..=3);
             let items: Vec<&'static str> =
@@ -58,10 +81,13 @@ impl Level for DictList {
                 .map(|i| Value::String((*i).to_string()))
                 .collect();
             inner.insert(Value::String((*name).to_string()), Value::Sequence(seq));
-            desc_chambers.push(ChamberDesc {
-                name: (*name).to_string(),
-                items: items.iter().map(|s| s.to_string()).collect(),
-            });
+
+            let be = if items.len() == 1 { "is" } else { "are" };
+            sentences.push(format!(
+                "There {be} {} inside {} {name}.",
+                join_items(&items),
+                article(name),
+            ));
         }
 
         let mut top = Mapping::new();
@@ -76,18 +102,13 @@ impl Level for DictList {
         let mut d = Describer::new();
         d.register(
             "l05",
-            "Several chambers branch off, each with its own inventory:\n\
-             {% for c in chambers %}\n{{ c.name }}:{% for it in c.items %}\n  - {{ it }}{% endfor %}\n{% endfor %}\n\
+            "Several chambers branch off, each with its own contents:\n\
+             {% for s in sentences %}\n  {{ s }}{% endfor %}\n\n\
              💡 Wrap the whole tree under a `chambers:` key — a dict of lists.",
         )
         .expect("register template");
         let description = d
-            .render(
-                "l05",
-                &DescCtx {
-                    chambers: desc_chambers,
-                },
-            )
+            .render("l05", &DescCtx { sentences })
             .expect("render template");
 
         Generated {