bracketed syntax @code{$[name]} and @code{@@[name]} must be used:
@example
@group
-if-stmt: IF '(' expr ')' THEN then.stmt ';'
+if-stmt: "if" '(' expr ')' "then" then.stmt ';'
@{ $[if-stmt] = new_if_stmt ($expr, $[then.stmt]); @}
@end group
@end example