#8581: Pattern synonym used in an expression context could have different constraints to pattern used in a pattern context -------------------------------------+------------------------------------- Reporter: cactus | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | Keywords: | 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 goldfire): Replying to [comment:39 dfeuer]:
I think what we actually want (borrowing from the [https://hackage.haskell.org/package/these these] package) is `These PatternType Type`. That is, either just the pattern, just the constructor, or both.
But this idea opens up a new, heretofore undiscussed possibility, that of a pattern synonym that cannot be used as a pattern. In other words, it would just be a normal Haskell variable, except with a capitalized identifier. I personally think this is one bridge too far, encouraging people to use a capitalized word for ordinary functions. I think this would be confusing, and for what benefit? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8581#comment:40 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler