#8582: Record syntax for pattern synonyms -------------------------------------+------------------------------------- Reporter: cactus | Owner: mpickering Type: feature request | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler | Version: Resolution: | Keywords: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 5144 | Blocking: Related Tickets: | Differential Rev(s): Phab:D1152 -------------------------------------+------------------------------------- Comment (by mpickering): Simon, I didn't want to write an explicit specification for this patch because it would amount to copying the specification for records. Which bit did you find confusing in the example I gave? In retrospect, the phrase "relevant data constructor" is confusing. So to explain, by "relevant" I mean an isomorphic (normally defined) data constructor. Does the example not make this any clearer? The problem with the implementation is with the record updates. Pattern synonym builders have required constraints which normal data constructors don't have. When the record update is desugared, it is necessary to provide the dictionaries for these constraints to the builder. My question was, how was I meant to do this. I ended up adding a field to the RecordUpd constructor which carried around the HsWrapper which then applied the dictionaries. More details are to be found in the last comment on the phab ticket. I don't have much time anymore to work on this ticket but I would be very disappointed it if did make it into GHC 8.0 as I started working on it several months ago. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8582#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler