#13128: Refactor AvailInfo to be more sensible -------------------------------------+------------------------------------- Reporter: mpickering | Owner: mpickering Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `AvailInfo` has been the bane of my life for the last 12 months and I want to tame it. There are two main problems with it. 1. There is this horrible invariant where if the parent is also exported then it is the first element of the list of children. 2. The set of children and field labels are represented as lists which means many expensive calls to functions from `ListSetOps`. 1 Is easy enough to solve by adding a flag which says whether the parent is exported or not. My naive attempt to solve the second problem was to replace the list by a `NameSet`. At the interface file boundary, the `NameSet` is converted into a list using `nameSetElemsStable` to maintain determinism and only pay the cost of using this expensive function once. This ran into problems in `RnModIface` where there are several functions which map over the list of children. NameSets don't support mapping and so this is difficult to implement in a satisfactory way. The next plan of attack is to distinguish between `IfaceAvailInfo` and `AvailInfo`. The former will use the old representation (lists) in order to maintain determinism but the latter will use sets. Distinguishing the two modes is useful conceptually and practically. The data type is used in quite a few different ways in lots of places which makes writing a nice interface hard. This ticket is to record my trail in case I don't make it to the end. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13128 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler