check point for review

compiler/parse/src/expr.rs

@@ -1086,9 +1086,18 @@ fn string_pattern<'a>() -> impl Parser<'a, Pattern<'a>> {
 }
 
 fn underscore_pattern<'a>() -> impl Parser<'a, Pattern<'a>> {
-    map_with_arena!(ascii_char(b'_'), |_arena, _thing| {
-        Pattern::Underscore(&"_")
-    })
+    move |arena: &'a Bump, state: State<'a>| {
+        let (_, next_state) = ascii_char(b'_').parse(arena, state)?;
+
+        let (output, final_state) = lowercase_ident().parse(arena, next_state)?;
+
+        let mut name = String::new_in(arena);
+
+        name.push('_');
+        name.push_str(output);
+
+        Ok((Pattern::Underscore(&"_"), final_state))
+    }
 }
 
 fn record_destructure<'a>(min_indent: u16) -> impl Parser<'a, Pattern<'a>> {