Replying to [comment:46 mpickering]:
Thanks for this detailed reply! I'm happy with all your responses save one:
- The spec says "We verify that the result types of each constructor in a complete match agrees with each other." What does this sentence mean? Consider the possibility of pattern synonyms that match against functions, polymorphic patterns, and possibly even higher-rank
#8779: Exhaustiveness checks for pattern synonyms -------------------------------------+------------------------------------- Reporter: nomeata | Owner: mpickering Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.1 checker) | Keywords: Resolution: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2669 Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): Replying to [comment:53 goldfire]: patterns.
It means that we look at the result type of each conlike and then verify that the type constructor for each type is the same. In the case of a set containing polymorphic patterns, at least one pattern in the set must have a definite type or you must specify a type signature to fix the type for the whole set.
I'm not sure what you mean here. Where do you specify the type signature? In the `COMPLETE` pragma?
I updated the wiki page now with lots of examples. You can specify something like.. {{{#!hs pattern P :: Maybe a pattern P = Nothing {-# COMPLETE P :: Maybe #-} }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8779#comment:55 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler