Does Frege solve the issue of “re-export qualified” of Haskell?

Question

The issue in Haskell:

 module Foo.A where foo = 42 

and

 module Foo.B where foo = 12 

and you want to write a super module

 module Foo ( module Foo.A , module Foo.B ) where import Foo.A import Foo.B 

which re-exports those modules, you would get a name clash.

Note, there can be plenty of the functions like foo in each module (foo1, foo2, etc) and I want to use them from both modules. There can also be data s with the same member names in each module, after all. So hiding isn't a solution. I do not consider Lens for resolving it.

Now, does Frege solve the problem of "re-export qualified" of Haskell? It seems it does if I remember correctly, but I can't find the evidence now, can anyone elaborate on that?

Answer 1

I guess it doesn't. In Frege, a module can re-export items only (ie functions, types, type classes), but not modules.

This means that, if you have some foo s down in the module hierarchy you are importing, you still need to hide all but at most one.

What you can do in Frege is:

import mod.A(foo fooA)
import mod.B(foo fooB)

which effectively renames A.foo to fooA and B.foo to fooB in the importing module. This works also on re-exports. For example, in frege.Prelude we have

import Prelude.PreludeBase public(!= /=)

This will cause anyone who imports frege.Prelude to have the operator /= available. But this is only an alias for the != operator of Ord

As one can imagine, we need to have both != and /= in order to avoid complaints form the Java or Haskell camps, respectively.