#9813: Error when reifying type constructor -------------------------------------+------------------------------------- Reporter: owst | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1899 Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): If we are willing to expose GHC's internal toposort of declarations (that is, its process of finding mutually recursive groups, without regard to top-to-bottom ordering, and then processing these groups in dependency order), then we might be able to do away with the stage restriction. Indeed, I was surprised to see that the Haskell 2010 report even contains a description of the toposort: see [https://www.haskell.org/onlinereport/haskell2010/haskellch4.html#x10-880004.... Section 4.5.1]. The context there is different than here, but it all still relies on finding chunks of perhaps-mutually-recursive definitions. So perhaps the process is this: 1. Split up the module into regions separated by top-level declaration splices. 2. Within each region, chunk the declarations into mutually recursive groups. Any declaration with a splice in it is considered to depend on all other declarations in the region. 3. Process the chunks in dependency order, making already-processed chunks available both for a. reification b. calling in a splice (i.e. loosening the stage restriction) I actually that's not quite so bad. It's not really too hard to understand. It might be some work to implement; it will depend on the details. But it surely seems ''possible'' to implement. And, as far as I can see, this is a loosening of existing restrictions. No code that is accepted today would be rejected by these rules. What do you think? And, in answer to your question, I don't think this is much related to #1831. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9813#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler