#10723: Make declarations in signatures "weakly bound" until they are used -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature request | Status: new Priority: normal | Milestone: Component: Package system | Version: 7.11 Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by ezyang): It is hard to say what will actually happen in practice until we have people actually using backpack, but I suspect that thinning only at the module level won't be enough. There are two reasons: 1. Think about the average Haskell module: it contains a lot of functions! This means that the normal signature someone will write for a module that already exists is going to have a lot of functions. Here, thinning at the expression level seems more important. 2. How are people going to write signatures? I think that for library level signatures, the best use of peoples time is for signatures to automatically be inferred from existing implementations rather than forcing people to write signatures all the time. So a signature will in general contain way too much stuff! Thinning definitely is necessary in this case. The benefit of implicit thinning is that, although it is strange from a language design perspective, it makes a lot of sense intuitively: there is no dependence on the import graph: a units requirements are completely specified as the set of requirements that it uses, and the set of requirements it available to includers. Yes, it is not syntactically evident what this is, but the whole point of a compiler is that you can get it to tell you what it is (eg some sort of Haddock documentation. Where as with thinning, sometimes it is not permissible to thin a requirement depending on whether it was imported by a module. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10723#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler