I've run across this too -- it's due to pandoc's use of a custom prelude in prelude/Prelude.hs (a recent change to make it easier to support multiple ghc versions).

I've reproduced the problem in the simplest possible way (without using stack or pandoc source). In an empty directory, create two files:

--- Prelude.hs
{-# LANGUAGE PackageImports #-}

module Prelude
(
  module P
, hi
)
where
import "base" Prelude as P
hi = print "hi"

-- test.hs
main = hi

Now ghc --make test.hs works fine. You get a test executable, which produces the output "hi" if you run it.

But ghci test.hs fils with the error

Top level:
    attempting to use module ‘Prelude’ (./Prelude.hs) which is not loaded

It seems to me that this is some kind of bug in ghci, but I'm not sure.

I posted the question here and learned of this bug report against ghci.

There's a workaround: we can add import Prelude to every source file, and add -XNoImplicitPrelude to the ghc-options field in pandoc.cabal. Then both cabal repl and stack ghci will work properly.

I made the change -- it took about 10 seconds with vim's 'bufdo'.

I've decided to handle this in a different way -- instead of explicitly importing Prelude and using NoImplicitPrelude, we now include the directory containing the custom Prelude only if ghc version is less than 7.10. It compiles on 4 GHC versions, but ghci will only work with ghc 7.10.x. This approach seems cleaner to me.