Import

The import statement is used to import functions and other definitions from another module. In the simplest case, you just write

import Data.Maybe

to import the named module (in this case Data.Maybe).

However, in more complicated cases, the module can be imported qualified, with or without hiding, and with or without renaming. Getting all of this straight in your head is quite tricky, so here is a table (lifted directly from the language reference manual) that roughly summarises the various possibilities:

Suppose that module Mod exports threefunctions named x, y and z. In that case:

Import command	What is brought into scope	Notes
import Mod	x, y, z, Mod.x, Mod.y, Mod.z	(By default, qualified and unqualified names.)
import Mod ()	(Nothing!)	(Useful for only importing instances of typeclasses and nothing else)
import Mod (x)	x, Mod.x	(Only x, no y or z.)
import qualified Mod	Mod.x, Mod.y, Mod.z	(Only qualified versions; no unqualified versions.)
import qualified Mod (x)	Mod.x	(Only x, only qualified.)
import Mod hiding ()	x, y, z, Mod.x, Mod.y, Mod.z	(Same as with no hiding.)
import Mod hiding (x)	y, z, Mod.y, Mod.z	(x is hidden.)
import qualified Mod hiding ()	Mod.x, Mod.y, Mod.z	(Same as with no hiding.)
import qualified Mod hiding (x)	Mod.y, Mod.z	(x is hidden.)
import Mod as Foo	x, y, z, Foo.x, Foo.y, Foo.z	(Unqualified names as before. Qualified names use Foo instead of Mod.)
import Mod as Foo (x)	x, Foo.x	(Only import x.)
import qualified Mod as Foo	Foo.x, Foo.y, Foo.z	(Only qualified names, using new qualifier.)