Simon Peyton-Jones wrote:
Concerning other mail on this subject, which has been v useful, I've revised the Wiki page (substantially) to take it into account. http://hackage.haskell.org/trac/ghc/wiki/GhcPackages
Further input (either by email or by adding material to the Wiki) would be welcome. (No guarantee Simon M agrees with what I've written... I'm at home this afternoon :-)
I think the following is a non-question: An open question: if A.B.C is in the package being compiled, and in an exposed package, and you say import A.B.C, do you get an error ("ambiguous import"), or does the current package override. because if the suggested syntax is used, import directives come in two flavours: ones that use "from" to import from a different package and ones that don't use "from" and therefore must refer to the current package. There would be no such thing as an "exposed" package (afaiu the idea of "exposure" is only needed in the context of different packages needing to share the same module namespace, which the proposal will hopefully make a thing of the past). Here are some other points: 1) What is the meaning of A.B.C.id ? I think this would have to refer to id in the module A.B.C in the package being compiled. To refer to an id in some other package, you'd have to use an alias eg import qualified A.B.C from "base" as P P.id -- P refers to the aliased module (Aliases hide modules in the current package with the same modid when that modid is used to qualify something) To avoid the need to use aliases here, a different syntax eg Base/A.B.C.id would need to be used (where Base is a package alias for "base") but it seems unlikely that anyone would find a reason to not want to use an alias in such cases so this other syntax wouldn't be necessary. 2) Exporting modules from other packages. (This also relates to the Haskell' proposal for qualified exports at http://hackage.haskell.org/trac/haskell-prime/wiki/ModuleSystem#Permitqualif... ) 2a) Exporting the contents of an external module module Foo ( module P ) where import qualified A.B.C from "extpkg" as P 2b) Exporting the contents of an external module qualified module Foo ( qualified module P ) where import qualified A.B.C from "extpkg" as P In both cases an alias would be needed so we can refer to the external module in the export list without having to repeat the 'from "extpkg"' here as well. And since we are using aliases, it makes sense to modify the poposed H' syntax to allow qualified module M to be short for: qualified module M as M where M is either an alias or a module in the current package. 3) Syntax: I liked Ian Lynagh's suggestion of using "from" to start either a single import directive or a block of import directives http://www.haskell.org//pipermail/haskell-cafe/2006-June/016338.html eg (modified to use quotes): from "base" import Predude hiding(length) import Control.Exception import qualified Data.List as List since otherwise it would soon become a bit of a pain to have to type 'from "base"' everywhere (esp if the package name was some long URL). It would also make it easier to quickly change to a different package without having to modify multiple import directives, which might be especially useful in the context of using a debug or release version of a package by putting C pre-processor directives around the "from" part. There is a minor open question about the exact indentation rule for the above syntax since "base" is not a keyword and it would seem strange to desugar it into from {"base"; import ... } so it looks like it would need a special layout rule that would give a desugaring into from "base" {import ...} Regards, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com