#13072: Move large tuples to a separate module in base -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: rwbarton Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: libraries/base | Version: 8.1 Resolution: | Keywords: 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 rwbarton): Unfortunately my claim
Anyone who does use the `GHC.LargeTuple` type family instances (even indirectly through another module) will have `GHC.LargeTuple` as a "family instances" import of their module
turns out not to be true. The family instances imports of a module are calculated from its imports, and at that point we don't know whether the module will mention any large tuples. For the same reason putting type family instances in a module where a wired-in thing lives is a dangerous thing to do in general, since we might read the wired-in module and learn about its instances and then use them without tracking their origin. (I found #13102 while writing the previous sentence.) I don't know whether there are existing occurrences of this in base, but it's exactly what I wanted to add. Note that adding an `import GHC.LargeTuple ()` to Prelude is not a complete solution either, since a module using large tuples and their Generic instance could have `-XNoImplicitPrelude`. So I don't have a solution that I'm really happy with here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13072#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler