From 2f48a4e058f7ddb7261e30bc7696e7326e6f7400 Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Tue, 21 May 2019 13:45:08 -0700
Subject: [PATCH] ; contributing: mention the need for a regular build before
 ghci

[ci skip]
---
 CONTRIBUTING.md | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index fe3713a64..7577de123 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1442,7 +1442,14 @@ Locally runs tests similar to what we run on Travis CI.
 
 ### Use GHCI
 
-GHCI is GHC's REPL, useful for exploring and calling code interactively.
+GHCI is GHC's [REPL](https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop), 
+useful for exploring and calling code interactively.
+
+If you try to run GHCI (or things based on it, like ghcid)
+right after cloning the hledger repo, you might see an error about CPP macros, eg like
+[on #961](https://github.com/simonmichael/hledger/issues/961#issuecomment-459283412).
+To fix this, build the hledger packages once, eg `stack build`.
+ (Or `stack build hledger` might be enough, depending what you are doing.)
 
 #### Get a GHCI prompt for hledger-lib: