Run with stack --resolver lts-11.1 ghci --package servant servant-server servant-lucid text network-uri

Test.hs

{-# LANGUAGE DataKinds         #-}
{-# LANGUAGE FlexibleContexts  #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeFamilies      #-}
{-# LANGUAGE TypeOperators     #-}
import Data.Monoid ((<>))
import qualified Data.Text as T
import Data.Text (Text)
import Network.URI (uriToString)
import Servant
import Servant.HTML.Lucid
import Servant.Utils.Links (safeLink)

mkLink :: (IsElem a Routes, HasLink a) => Proxy a -> MkLink a
mkLink = safeLink (Proxy :: Proxy Routes)
routeToText :: (IsElem a Routes, HasLink a, ToHttpApiData (MkLink a))
  => Proxy a
  -> Text
routeToText = toUrlPiece . routeToURI

routeToURI :: (IsElem a Routes, HasLink a) => Proxy a -> MkLink a
routeToURI = safeLink (Proxy :: Proxy Routes)


type ShowProfileR   = "user" :> Capture "profileName" Text :> Get '[HTML] (Text)
type ShowProfilesR  = "user" :> Get '[HTML] (Text)

type Routes = ShowProfileR :<|> ShowProfilesR

example :: Text
example = routeToText (Proxy :: Proxy ShowProfilesR)

example2 :: Text
example2 = toUrlPiece $ safeLink (Proxy :: Proxy Routes) (Proxy :: Proxy ShowProfileR) "username"

-- Does not work
--example3 :: Text
--example3 = routeToText (Proxy :: Proxy ShowProfileR) "username"