\____/\/ /_/\____/|_| Type :? for help.
Loading package std ... linking ... done.
-*** WARNING: . is writable by someone else, IGNORING!
-*** WARNING: ./.ghci is writable by someone else, IGNORING!
Prelude> :unset +s +t
Prelude> -- tests for :def, :undef
Prelude> let void m = m >> return ""
hello, world!
Prelude> :echo hello, world!
Prelude> :def echo echo
+hello, world!
command `echo' is already defined
Prelude> :undef echo
Prelude> :def echo echo
Prelude> :echo hello, world!
HELLO, WORLD!
Prelude> Leaving GHCi.
-hello, world!