Add prelude and while macro

This commit introduces a new prelude file that defines the `while` macro
and registers it during environment bootstrapping. The `again` macro has
been updated to accept multiple arguments for its recursive call, and
several examples have been adjusted to reflect this change.
Additionally, the `MacroRegistry` in the compiler is now cloneable and
can be moved out of the `MacroExpander`.

src/ast/parser.rs

@@ -153,10 +153,23 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_again(&mut self, identity: Identity) -> Result<Node<UntypedKind>, String> {
-        let args = Box::new(self.parse_expression()?);
+        let mut elements = Vec::new();
+
+        while *self.peek() != TokenKind::RightParen && *self.peek() != TokenKind::EOF {
+            elements.push(self.parse_expression()?);
+        }
+
+        let args_node = Node {
+            identity: identity.clone(),
+            kind: UntypedKind::Tuple { elements },
+            ty: (),
+        };
+
         Ok(Node {
             identity,
-            kind: UntypedKind::Again { args },
+            kind: UntypedKind::Again {
+                args: Box::new(args_node),
+            },
             ty: (),
         })
     }