#8779: Exhaustiveness checks for pattern synonyms -------------------------------------+------------------------------------- Reporter: nomeata | Owner: 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): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): The ticket mentions
Multiple pragmas are obviously combined with `||`, and there is an implicit `{-# COMPLETE_PATTERNS [] && (:) #-}` listing all real data constructors.
which sounds like {{{#!hs {-# COMPLETE_PATTERNS Empty, (:<|) #-} {-# COMPLETE_PATTERNS Empty, (:|>) #-} }}} would equal what I proposed (if I got the precedence right) {{{#!hs {-# COMPLETE_PATTERNS Empty, (:<|) | Empty, (:|>) #-} }}} ---- Tangent: The second part (“there is an implicit `{-# COMPLETE_PATTERNS [] && (:) #-}` listing all real data constructors.”) sounds awful similar to this part of the [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/pragmas.html users guide]:
If no MINIMAL pragma is given in the class declaration, it is just as if a pragma {{{#!hs {-# MINIMAL op1, op2, ..., opn #-} }}} was given, where the `opi` are the methods a. that lack a default method in the class declaration, and b. whose name that does not start with an underscore (c.f. -fwarn- missing-methods, Section 4.8, “Warnings and sanity-checking”).
As I understand it means that when the user defines {{{#!hs data ABC = A | B | C }}} it is as if the she had also written `{-# COMPLETE_PATTERNS A, B, C #-}`. Would this work with GADTs? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8779#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler