Bar.hs

{-# LANGUAGE TemplateHaskell #-}
module Bar (bar) where
import Foo (foo)

bar = $foo ++ "bar"

Foo.hs

module Foo (foo) where
import Language.Haskell.TH

foo :: ExpQ
foo = stringE "foo"

Main.hs

import Bar (bar)

main = putStrLn bar