[Agda] problems configuring haskell-mode and/or invoking cabal repl

[Martin Stone Davis]

I'm trying to use the emacs haskell-mode to hack Agda but am getting 
warnings and errors. When I C-c C-l on a file, say 
src/full/Agda/Main.hs, I get a Compilation Error from the warning:

> src/full/Agda/Utils/Map.hs:30:9-48: warning: 
> [-Wmonomorphism-restriction] …

Also, when I cabal repl --ghc-option=-ferror-spans I also get a bunch of 
warnings like:

> Warning: Can't find file "dist-2.6.0/build/autogen/cabal_macros.h" in 
> directories
I do have a cabal-macros.h but it's in dist (not dist-2.6.0).

I am able to cabal install Agda (lastest master version) with no 
problems. I'm using emacs-haskell-mode 13.20 in emacs 25.1.1.