In short, this should work:

hi("some string").split(/\s+/)

Anywhere that accepts a consumer should also accept and automatically convert a regular expression object.

As of writing there are converters for predicates and sequence inputs, but none for regex objects. It should be possible (if a bit tricky) to write a consumer type whose behavior is determined by a regular expression

Supporting regex lookaround should not be part of this issue. After this issue is resolved, then whether or not to support this feature should be re-evaluated. At present, it looks as though adding support for lookaround would require a substantial increase in complexity for consumers and any code that uses them.