Editing Import (section)

===Hiding Prelude===

By default, ''every module'' implicitly imports <hask>Prelude</hask>. However, if you add an ''explicit'' import declaration for the prelude, this turns off the implicit one. Thus, if you wanted (for example) to write a module that redefines <hask>zip</hask> you could do
<haskell>
module Mod where

import Prelude hiding (zip)

zip = {- ... -}
</haskell>
Without the <hask>import</hask> statement, you could receive a compile-time error about an 'ambiguous use of <hask>zip</hask>'. A slightly more messy alternative is to do
<haskell>
module Mod where

import qualified Prelude as P

zip = {- ... -}
</haskell>
This has the disadvantage that (say) '<hask>P.show (2 P.+ 3 P.* 3) P.++ "abc"</hask>' is very messy to read. Typically a module only redefines a few prelude functions, and it's simpler to just hide the ones you don't want to clash with.

Note that any module ''using'' a module that redefines prelude functions will need to import either the prelude or the other module (or maybe both) qualified and/or with hiding for the same reason.