[Haskell-cafe] Re: Status of TypeDirectedNameResolution proposal?

[Ben Millwood]

On Sun, Nov 22, 2009 at 7:13 PM, Ketil Malde <ketil at malde.org> wrote:
>
> 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).

The obvious question arising here is what if module Foo.Bar *is* found
in Foo/Bar.hs as well as in Foo.hs - is the latter ignored? It doesn't
sound like an insurmountable problem but one of the nicest things
about the current module system is its simplicity and predictability,
both of which are somewhat attacked by this proposal.
Also, it sounds like your proposal would disallow definition of
multiple top-level modules in a file, because we wouldn't know where
to look for them. This is not necessarily unreasonable, but it's an
unexpected special case.
Presumably having the modules together in a file would also mean that
they could only be compiled together and would produce a single .o or
.hi file. Then you might ask whether the ABI or whatever is
necessarily broken by a change to *any* of the modules involved, in
which case modularisation starts to become purely about name
qualification. Thinking about that, it's worth noting that importing
one module twice with two different names works fine.
This is not to say I'm against the proposal, but it's probably not as
clear-cut as it sounds.