GHC/Maybe.hs

    {-# LANGUAGE NoImplicitPrelude #-}
    {-# OPTIONS_HADDOCK not-home #-}

    -- | Maybe type
    module GHC.Maybe
       ( Maybe (..)
       )
    where

    import GHC.Integer () -- See Note [Depend on GHC.Integer] in GHC.Base
    import GHC.Classes

    default ()

    -------------------------------------------------------------------------------
    -- Maybe type
    -------------------------------------------------------------------------------

    -- | The 'Maybe' type encapsulates an optional value.  A value of type
    -- @'Maybe' a@ either contains a value of type @a@ (represented as @'Just' a@),
    -- or it is empty (represented as 'Nothing').  Using 'Maybe' is a good way to
    -- deal with errors or exceptional cases without resorting to drastic
    -- measures such as 'Prelude.error'.
    --
    -- The 'Maybe' type is also a monad.  It is a simple kind of error
    -- monad, where all errors are represented by 'Nothing'.  A richer
    -- error monad can be built using the 'Data.Either.Either' type.
    --
    data  Maybe a  =  Nothing | Just a
      deriving ( Eq  -- ^ @since 2.01
               , Ord -- ^ @since 2.01
               )