case-insensitive-0.2: Data/CaseInsensitive.hs

{-# LANGUAGE NoImplicitPrelude
           , UnicodeSyntax
           , TypeSynonymInstances
           , DeriveDataTypeable
  #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Data.CaseInsensitive
-- Copyright   :  (c) 2011 Bas van Dijk
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Bas van Dijk <v.dijk.bas@gmail.com>
--
-- This module is intended to be imported qualified. May I suggest:
--
-- @
-- import          Data.CaseInsensitive   ( CI )
-- import qualifed Data.CaseInsensitivee as CI
-- @
--
-----------------------------------------------------------------------------

module Data.CaseInsensitive ( CI
                            , mk
                            , original
                            , foldedCase
                            , map
                            , FoldCase(foldCase)
                            ) where

--------------------------------------------------------------------------------
-- Imports
--------------------------------------------------------------------------------

-- from base:
import Data.Char     ( toLower )
import Data.Eq       ( Eq((==)) )
import Data.Ord      ( Ord(compare) )
import Data.Function ( on )
import Data.Functor  ( fmap )
import Data.Monoid   ( Monoid(mempty, mappend) )
import Data.String   ( IsString(fromString) )
import Data.Typeable ( Typeable )
import Data.Char     ( Char )
import Prelude       ( String )
import Text.Read     ( Read(readPrec) )
import Text.Show     ( Show(showsPrec), ShowS )
import qualified Data.List as L ( map )

-- from base-unicode-symbols:
import Data.Function.Unicode ( (∘) )

-- from bytestring:
import qualified Data.ByteString             as B    ( ByteString )
import qualified Data.ByteString.Lazy        as BL   ( ByteString )
import qualified Data.ByteString.Char8       as C8   ( map )
import qualified Data.ByteString.Lazy.Char8  as BLC8 ( map )

-- from text:
import qualified Data.Text      as T  ( Text, toCaseFold )
import qualified Data.Text.Lazy as TL ( Text, toCaseFold )


--------------------------------------------------------------------------------
-- Case Insensitive Strings
--------------------------------------------------------------------------------

{-| A @CI s@ provides /C/ase /I/nsensitive comparison for the string-like type
@s@ (for example: 'String', 'T.Text', 'B.ByteString', 'ShowS', etc.).

Note that @CI s@ has an instance for 'IsString' which together with the
@OverloadedStrings@ language extension allows you to write case insensitive
string literals as in:

@
\> (\"Content-Type\" :: 'CI' 'T.Text') == (\"CONTENT-TYPE\" :: 'CI' 'T.Text')
True
@

-}
data CI s = CI { original   ∷ !s -- ^ Retrieve the original string-like value.
               , foldedCase ∷ !s -- ^ Retrieve the case folded string-like value.
                                 --   (Also see 'foldCase').
               }
          deriving Typeable

-- | Make the given string-like value case insensitive.
mk ∷ FoldCase s ⇒ s → CI s
mk s = CI s (foldCase s)

-- | Transform the original string-like value but keep it case insensitive.
map ∷ FoldCase s2 ⇒ (s1 → s2) → (CI s1 → CI s2)
map f = mk ∘ f ∘ original

instance (IsString s, FoldCase s) ⇒ IsString (CI s) where
    fromString = mk ∘ fromString

instance Monoid s ⇒ Monoid (CI s) where
    mempty = CI mempty mempty
    CI o1 l1 `mappend` CI o2 l2 = CI (o1 `mappend` o2) (l1 `mappend` l2)

instance Eq s ⇒ Eq (CI s) where
    (==) = (==) `on` foldedCase

instance Ord s ⇒ Ord (CI s) where
    compare = compare `on` foldedCase

instance (Read s, FoldCase s) ⇒ Read (CI s) where
    readPrec = fmap mk readPrec

instance Show s ⇒ Show (CI s) where
    showsPrec prec = showsPrec prec ∘ original


--------------------------------------------------------------------------------
-- Folding (lowering) cases
--------------------------------------------------------------------------------

-- | Class of string-like types that support folding cases.
--
-- Note that the instances for 'Char', 'String', 'ShowS' and the 'B.ByteString'
-- types do /not/ perform fully correct Unicode-aware case folding, they simply
-- 'toLower' their characters! This is of course more than suitable for ASCII
-- encoded strings.
--
-- The instances for the 'T.Text' types use 'T.toCaseFold' which performs a
-- better Unicode-aware case fold which is more suitable for case insensitive
-- string comparisons.
class FoldCase s where foldCase ∷ s → s

instance FoldCase Char          where foldCase = toLower
instance FoldCase String        where foldCase = L.map toLower
instance FoldCase B.ByteString  where foldCase = C8.map toLower
instance FoldCase BL.ByteString where foldCase = BLC8.map toLower
instance FoldCase T.Text        where foldCase = T.toCaseFold
instance FoldCase TL.Text       where foldCase = TL.toCaseFold
instance FoldCase ShowS         where foldCase = (foldCase ∘)
instance FoldCase (CI s)        where foldCase (CI _ l) = CI l l


-- The End ---------------------------------------------------------------------