#16240: Core visible conditional compilation/static definition/code selection based upon static key values -------------------------------------+------------------------------------- Reporter: carter | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.7 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 AndreasK): Replying to [comment:1 carter]:
forgot to add: each map assignment would correspond to a different typing environment if we wanted to check types under each combination ..
There are valid use cases for CPP with code which doesn't compile/type check at all under one of the variants on a specific system. Primarily when libraries/ghc add new features and only the old version is available. Eg I don't see how this would be enough if a base version uses a different class definition for Monoid. You would need both definitions to type check both variants, which in general is not always possible. So ideally we want to support both: * Essentially string replacement * Typechecking of both variants. Unless you want to restrict HPP to certain use cases and fall back to CPP for other ones. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16240#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler