Scheme

[Scott David Daniels]

One language to look at for its mind-expanding possibilities is
icon.  I don't know anyone who ever stayed there for more than
a few years, but it does provide a follow-through on result sets
and failure as empty result sets.  I suspect you might find it a
"wonderful and rewarding journey" if you are looking for new
intuitions into what code can express.

Prolog is another language with (to my mind) lousy aesthetics, but
a fine mind-stretcher.

-Scott David Daniels
Scott.Daniels at Acm.Org