Can a GHCI config file use CPP macros?

Question

I was thinking it would be nice to set up my global GHCI config such that my commonly-used imports occur automatically when the packages that provide them are present.

I tried adding this to ~/.ghc/ghci.conf:

:set -XCPP

#ifdef MIN_VERSION_containers
import           Data.Set (Set)
import qualified Data.Set as Set
import           Data.Map (Map)
import qualified Data.Map as Map
#endif

But apparently that does not work.

> stack repl
Configuring GHCi with the following packages: 
GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help

<interactive>:24:1: error: parse error on input ‘#’

<interactive>:29:1: error: parse error on input ‘#’

Is there a way to get CPP macros to work, or some other way to accomplish what I'm trying to do?

Answer 1

Those macros cannot be used directly by GHCI, but they can be used in a file you include using GHCI's :add command.

For example, this is what my setup now looks like:

• ~/.ghc/ghci.conf contains the :add command:

  > grep imports ~/.ghc/ghci.conf
  :add /home/chris/.ghc/imports.hs
  

• ~/.ghc/imports/imports.hs contains my CPP'ed imports:

  > cat ~/.ghc/imports/imports.hs
  {-# LANGUAGE CPP #-}
  
  #ifdef MIN_VERSION_containers
  import           Data.Set (Set)
  import qualified Data.Set as Set
  import           Data.Map (Map)
  import qualified Data.Map as Map
  #endif