#10478: Shorter import syntax -------------------------------------+------------------------------------- Reporter: acowley | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by goldfire): 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? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10478#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler