{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
import Data.Proxy
import GHC.TypeLits

prefixed [] s = Just s
prefixed (p:ps) (s:ss) | p == s = prefixed ps ss
prefixed _ _ = Nothing

pattern Prefixed :: forall (s :: Symbol). KnownSymbol s => String -> String
pattern Prefixed x <- (prefixed (symbolVal (Proxy @s)) -> Just x)

secure (Prefixed @"https://" x) = x ++ " is secured"
secure _ = "insecure"

main :: IO ()
main = print (secure "https://hi", secure "http://bad")