Robert Greayer
allow local modules.
module Foo where module Bar where data Bar = Bar { x :: Int, y :: Int } module Baz where data Baz = Baz { x :: Int, y :: Int }
f a b = Bar.x a + Baz.y b
Independent of TDNR I would welcome this. Maybe Ticket 2551 ("Allow multiple modules per source file") [1] should be reconsidered.
Although ticket 2551 is not exactly what Luke is suggesting (which would be an extension to the language, whereas, if I'm not mistaken, 2551 is just a change to where GHC can find modules, not nesting of modules).
I think this would be great, and have very few negative consequences. Having multiple modules per file would make it a lot more convenient to define tiny modules and use namespacing more actively. E.g. if module Foo.Bar isn't found in Foo/Bar.hs GHC could look in Foo.hs (which would just contain a concatenation of what would currently reside in Foo.hs and Foo/Bar.hs). So, Foo.hs could contain:
module Foo.Bar where data Bar = Bar { x :: Int, y :: Int }
module Foo.Baz where data Baz = Baz { x :: Int, y :: Int }
module Foo where import Foo.Bar as Bar import Foo.Baz as Baz
f a b = Bar.x a + Baz.y b
Since modules are already hierarchical, and there is already a mechanism for scoping/qualification, I'm not sure modifying the language to allow nesting actually buys anything. Or? -k -- If I haven't seen further, it is by standing in the footprints of giants