#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 owst): Replying to [comment:31 simonpj]:
Yes, this is the main reason for the fairly draconian staging restriction at present. But that's only when you want to RUN a splice. If you merely want to reify a type declared "earlier" (as in the Description of this ticket), that's much less stressful. But it exists already {{{ data F = MkF $(makeLenses 'F) }}}
Absolutely, since `F` is defined in the ''previous'' declaration group to `makeLenses 'F`. My proposal is to allow: {{{ data F = MkF f x = x g = $(mapM reify [''F, 'MkF, 'f] ...) }}} to work too (i.e. allow access via `reify` to (certain) declarations in the ''same'' declaration group). Implementation-wise, I can imagine that the changes will be something along the lines of: 1. Partition the expressions in a declaration group into those that contain splices, and those that do not, 1. Make each expression that contains a splice implicitly depend on all expressions that do not contain splices, 1. Traverse the the toposorted dependency graph and mark all nodes below or containing a splice as "splicy", 1. Process all nodes that are not marked splicy, 1. Make available the information about the non-splicy nodes in the environment, 1. Process all splicy nodes. Presumably, much of this can be taken from the code used to implement the features pointed out by Simon. I will likely start taking a serious look at this tonight. Any pointers/suggestions gratefully received! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9813#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler