Bar.hs

module Bar where

bar = answer * 2

Foo.hs

{-# LANGUAGE NoMonomorphismRestriction #-}
import Language.Haskell.Interpreter

foo = runInterpreter (do
  reset
  loadModules ["Bar", "Prelude"]
  setTopLevelModules ["Bar"]
  eval "bar")

Prelude.hs

{-# LANGUAGE PackageImports #-}

module Prelude (String, Show(..), Num(..), answer) where

import "base" Prelude (String, Show(..), Num(..))

answer = 42