:unset +s +t
-- tests for :def, :undef
:def
let void m = m >> return ""
let echo s = void (putStrLn s)
:def echo echo
:def
:echo hello, world!

let echoupper s = return (":! echo " ++ map Data.Char.toUpper s)
:echo hello, world!
:def echo echoupper
:undef echo
:def echo echoupper
:echo hello, world!
:def! echo echo
:echo hello, world!
:undef f f