Use-defined guard (was: RE: Enhanced type guard syntax])

[Richard A. O'Keefe]

"Fredrik Linder" <fredrik.linder@REDACTED>	However, by allowing only a limited set of operations in guard-declared
	functions (such as only allowing then to call other guard-functions) could
	be the fine line that increases usability while still preserving the
	consistency of the program.
	
	The usage I am targeting is to have user-defined guards as
	inspectors/selectors on ADTs.
	
Except for the unnecessarily ugly syntax and not being quite as fully
worked out, how is this different from my old "Abstract Patterns" proposal?