{-# LANGUAGE TypeFamilies #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE PolyKinds #-} -- removes need to annotate kinds as [Symbol] -- | Encoding safe version of "Data.ByteString.Char8" -- @since 0.2.2.0 module Data.TypedEncoding.Conv.ByteString.Char8 where import qualified Data.ByteString.Char8 as B8 import qualified Data.TypedEncoding.Common.Util.TypeLits as Knds import Data.TypedEncoding.Instances.Support -- $setup -- >>> :set -XDataKinds -XTypeApplications -XOverloadedStrings -- | -- Type safer version of 'Data.ByteString.Char8.pack'. -- -- This assumes that each of the encodings in @xs@ work work equivalently in @String@ and @ByteString@. -- -- Because of how @ByteString.Char8.pack@ works, the first encoding (last in the list) must restrict character set to a subset of @ASCII@. -- -- Currently this uses (an over-conservative) @"r-ASCII"@ superset constraint, in the future, this could be relaxed to a superset of /ASCII/, e.g. /r-CHAR8/ when one is in place. -- -- >>> :t pack (undefined :: Enc '["r-bar", "r-foo"] () String) -- ... -- ... error: -- ... Couldn't match type ... -- ... "r-ASCII" "r-foo" ... -- ... -- -- >>> displ $ pack (unsafeSetPayload () "Hello" :: Enc '["r-bar", "r-ASCII"] () String) -- "Enc '[r-bar,r-ASCII] () (ByteString Hello)" pack :: (Knds.LLast xs ~ t, IsSuperset "r-ASCII" t ~ 'True) => Enc xs c String -> Enc xs c B8.ByteString pack = unsafeChangePayload B8.pack -- | @unpack@ on encoded strings. -- -- See 'pack' unpack :: (Knds.LLast xs ~ t, IsSuperset "r-ASCII" t ~ 'True) => Enc xs c B8.ByteString -> Enc xs c String unpack = unsafeChangePayload B8.unpack -- TODO consider adding "r-CHAR8"