#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 rwbarton): This all sounds great except for one thing. Do we have a plan for actually loosening the stage restriction? The stage restriction exists for technical reasons, not conceptual reasons. The stage restriction currently applies to the module as a whole. It says you cannot use an identifier that was defined in a module within a splice in the same module. Clearly if the use is in a later declaration group than the definition, there is no problem in principle with lifting the restriction. But in order to do so, we would have to run the declaration group containing the definition through the entire compiler pipeline, right up to linking, so that we can load it to run the splice in the latter declaration group to begin type checking it. GHC just isn't organized to work that way currently. The user's guide has this to say on the subject:
You can only run a function at compile time if it is imported from another module. That is, you can't define a function in a module, and call it from within a splice in the same module. (It would make sense to do so, but it's hard to implement.)
-- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9813#comment:27 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler