[racket] set!: eval-ing to lvalues

Stephen Chang wrote:

> Reminds me of this:
> http://james-iry.blogspot.com/2009/05/brief-incomplete-and-mostly-wrong.html
>
> 1990 - A committee formed by Simon Peyton-Jones, Paul Hudak, Philip
> Wadler, Ashton Kutcher, and People for the Ethical Treatment of
> Animals creates Haskell, a pure, non-strict, functional language.
> Haskell gets some resistance due to the complexity of using monads to
> control side effects. Wadler tries to appease critics by explaining
> that "a monad is a monoid in the category of endofunctors, what's the
> problem?"

Philip Wadler retro-legitimized this quote by saying it during a panel 
discussion at the Haskell Symposium 2013 (affiliated with ICFP), which 
made my whole month. --PR