Can I export constructors along with a type alias?

Question

I have a data type data Foo a b = Bar a b that I use internally in a library.

I also have an alias for one of its more common concrete forms: type

Answer 1

You can export Bar type simply by module Quux (Bar) where ..., though you will not be able to construct any Bars.

If you also need the constructor, you may use similar technique to smart constructors, that is create a helper functions which creates Bars and export that one:

module Quux (Bar, bar) where

data Foo a b = Foo a b
type Bar = Foo Int Int

bar :: Int -> Int -> Bar
bar = Foo

then

\> let b = bar 1 2
\> :type b
b :: Bar
\> let f = Foo 1 2

:9:9: Not in scope: data constructor ‘Foo’