I'm in favor of abbreviating the syntax in this common scenario, but I don't like your choice of syntax, I'm afraid. It would give
{{{
import Data.Map (Map) as M -- (1)
}}}
a very different meaning from
{{{
import Data.Map as M (Map) -- (2)
}}}
(1) imports all of `Data.Map`, qualified with the alias `M`, and imports the name `Map` unqualified. (2) imports only the name `Map` (unqualified) while also aliasing `Data.Map`.
Having these two coexist seems like we're asking users to be confused.
What about
{{{
import Data.Map (Map)
qualified as M *
}}}
?
The general schema, which replaces the current syntax. This schema does not permit some current syntax, but it would be easy to extend it to be backward-compatible. I've chosen not to for this presentation to avoid clutter.
{{{
import_statement ::= 'import' module_name maybe_name_list import_specifiers
module_name ::= ...
maybe_name_list ::= name_list | <empty>
name_list ::= '(' names ')' | '*'
import_specifiers ::= <empty> | import_specifier import_specifiers
import_specifier ::= 'hiding' name_list | qualified_spec name_list
qualified_spec ::= 'qualified' | 'qualified' 'as' name
}}}
The top-level `maybe_name_list` would list all unqualified imports. If it is omitted, and there are no `qualified_spec`s, then all names would be imported unqualified. If it is omitted and there are one or more `qualified_spec`s, then no names would be imported unqualified.
Each `import_specifier` either adds qualified names (perhaps under a module synonym) or removes names. Removing names with `hiding` removes those names from the `qualified_spec` (or top-level `maybe_name_list`) immediately preceding the `hiding`.
The special `name_list` `*` (note that it is ''not'' in parentheses, to avoid ambiguity) means "all names".
This schema allows one import statement to import a mix of qualified and unqualified names, and even allows using different module synonyms for different sets of qualified names. The legacy `import` syntax could desugar to this form, which seems strictly more expressive. For example:
{{{
import qualified Foo --> import Foo qualified *
import qualified Bar as B --> import Bar qualified as B *
import Baz hiding (wurble) --> import Baz hiding (wurble)
}}}
Thoughts?