Here's a brief list of gotchas when moving DIRM code to newer
DRM-based implementations:

- Rename union to type-union.
- while and until in for loops are now while: and until:.
- Exception clauses in blocks now require the exception to be
  surrounded by parentheses.
- Methods on generic functions must exactly match the GF signature.
  For instance, for methods on forward-iteration-protocol, you need
  to declare the return type as being six functions.
- add() on lists may share structure.
- Replace class-for-copy with type-for-copy.
- Change calls which depend upon the return types of push, push-last,
  or remove-key!.
