When it starts, GHCi always reads and executes commands from
$HOME/.ghci, followed by
./.ghci.
The .ghci in your home directory is
most useful for turning on favourite options (eg. :set
+s), and defining useful macros. Placing a
.ghci file in a directory with a Haskell
project is a useful way to set certain project-wide options so you
don't have to type them everytime you start GHCi: eg. if your
project uses GHC extensions and CPP, and has source files in three
subdirectories A B and C, you might put the following lines in
.ghci:
:set -fglasgow-exts -cpp :set -iA:B:C
(Note that strictly speaking the -i flag is
a static one, but in fact it works to set it using
:set like this. The changes won't take effect
until the next :load, though.)
Two command-line options control whether the
.ghci files are read: