Type level BEM declarations because why not....

bem.hs

data CSS_BEM (block :: Symbol) = CSS_BEM
  { cssBEMBlock :: Text
  , cssBEMElem :: Text -> Text
  , cssBEMMod :: Text -> Text
  , cssBEMElemMod :: Text -> Text -> Text
  }

mkCSSBEM :: forall t. KnownSymbol t => CSS_BEM t
mkCSSBEM = CSS_BEM @t tb (mappend tb__) (mappend (tb <> "--")) (\e m -> tb__ <> e <> "--" <> m)
  where
    tb__ = tb <> "__"
    tb = T.pack (symbolVal (Proxy @t))

setupBEM :: CSS_BEM "setup"
setupBEM = mkCSSBEM

{-
*BEM> cssBEMElem setupBEM "wrapper"
"setup__wrapper"
*BEM> cssBEMMod setupBEM "hidden"
"setup--hidden"
*BEM> cssBEMElemMod setupBEM "wrapper" "hidden"
"setup__wrapper--hidden"
*BEM> cssBEMBlock setupBEM 
"setup"
*BEM> 
-}