[plt-scheme] HtDP Section 14: stricter typing for eye color?

On Feb 15, 2004, at 11:32 PM, Robby Findler wrote:
>
> Of course, the real question is how to enforce them. For one answer,
> see Cormac Flanagan's dissertation (and related papers on MrSpidey). He
> uses a set-based analysis to compute a set of values for each program
> point and his system can accommodate such types as above.

Is there some good reason not to mention your (Robby) work on contracts 
in this instance?

PLT Scheme's contracts (search for "contract" in Help Desk) provide one 
way to enforce such restrictions.

john