I fail to see how this would work for recursive examples like the
#15305: Erroneous "non-exhaustive pattern match" using nested GADT with strictness annotation -------------------------------------+------------------------------------- Reporter: jkoppel | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Research Component: Compiler (Type | needed checker) | Version: 8.4.3 Resolution: | Keywords: | PatternMatchWarnings Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple error/warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): program in comment:7 Correct. Computing `NonVoid( tau )` is an open-ended question. For some `tau`s (lke `Bar A`) it's easy; for others we could be more ambitious. It's probably undecidable in general. So we could start with something simple and become more ambitious later. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15305#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler