Group.hs

-- | ASCII characters are broadly categorized into two groups:
--   /control codes/ and /printable characters/.
module ASCII.Group
  ( -- * The @Group@ type
    Group (..),

    -- * Functions
    charGroup,
    inGroup,

    -- * Notes
    -- $notes
  )
where

import ASCII.Char (Char)
import ASCII.Char qualified as Char
import Data.Bool (Bool)
import Data.Data (Data)
import Data.Eq (Eq, (==))
import Data.Hashable (Hashable)
import Data.Ord (Ord, (<))
import GHC.Generics (Generic)
import Text.Show (Show)
import Prelude (Bounded, Enum)

data Group
  = -- | 33 of the ASCII characters are /control codes/.
    -- A few of these are still in use, but most are obsolete relics of the early days of computing.
    Control
  | -- | 95 of the ASCII characters are /printable characters/ such as letters and numbers,
    -- mostly corresponding to the keys on an American English keyboard.
    Printable

deriving stock instance Eq Group

deriving stock instance Ord Group

deriving stock instance Enum Group

deriving stock instance Bounded Group

deriving stock instance Show Group

deriving stock instance Data Group

deriving stock instance Generic Group

deriving anyclass instance Hashable Group

-- | Determine which group a particular character belongs to
--
-- >>> map charGroup [CapitalLetterA,EndOfTransmission]
-- [Printable,Control]
charGroup :: Char -> Group
charGroup x =
  case x of
    _ | (x < Char.Space) -> Control
    Char.Delete -> Control
    _ -> Printable

-- | Test whether a character belongs to a particular group
--
-- >>> inGroup Printable EndOfTransmission
-- False
--
-- >>> inGroup Control EndOfTransmission
-- True
inGroup :: Group -> Char -> Bool
inGroup g x = charGroup x == g

-- $notes
--
-- Space is a printable character (perhaps surprisingly, given that it is invisible).
--
-- >>> charGroup Space
-- Printable
--
-- Tab is a control code (perhaps surprisingly, given that space is a printable character).
--
-- >>> charGroup HorizontalTab
-- Control
--
-- A few examples of printable characters:
--
-- >>> all (inGroup Printable) [CapitalLetterA,SmallLetterZ,Digit4,Tilde]
-- True
--
-- A few examples of control characters:
--
-- >>> all (inGroup Control) [Null,Substitute,UnitSeparator,Delete]
-- True
--
-- There are 33 control codes.
--
-- >>> length (filter (inGroup Control) allCharacters)
-- 33
--
-- There are 95 printable characters.
--
-- >>> length (filter (inGroup Printable) allCharacters)
-- 95