static-text provides type-level safety for basic operations on
string-like types (finite lists of elements), such as Data.Text,
String (and all lists), Data.ByteString and Data.Vector. Use it
when you need static guarantee on lengths of strings produced in your
code.
An example application would be a network exchange protocol built of packets with fixed-width fields:
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
import Data.ByteString.Char8 (ByteString, pack)
import Data.StaticText
mkPacket :: ByteString -> Static ByteString 32
mkPacket inp =
-- 5-character version signature
$(st "PKT10") `append`
-- 25-character payload
payload `append`
-- 2-character payload checksum
checksum
where
payload = createLeft 0x20 inp
checksum :: Static ByteString 2
checksum = createLeft 0x20 $
pack $ show $ Data.StaticText.length payload `mod` 100
message :: Static ByteString 64
message = mkPacket "Hello" `append` mkPacket "world"
main :: IO ()
main = print messagePlease consult the Hackage page for static-text for documentation and examples.
The emphasis of static-text is on type-safe padding/truncation and type-safe string literals. Other similar libraries may suit different use cases:
- vector-sized and fixed-vector: full support for Vector API, but not string-like types.