[PRL] annoying types ARGH!

[Matthias Felleisen]

I just wrote this little program for Karl:

> type posn = float * float;;
>
> type shape =
>        Circle of posn * float
>      | Square of posn * float * float
>      | Union of shape * shape;;
>
> let distance((x1,y1),(x2,y2)) =
>     let dx = x1 -. x2 in
>     let dy = y1 -. y2 in
>       sqrt(dx *. dx +. dy *. dy)
>
> let rec inShape(s,p)  = match s with
>     Circle(c,r) -> distance(c,p) <= r
>   | Square(nw,width,height) -> false
>   | Union(top,bot) -> inShape(top,p) || inShape(bot,p);;

Before I finished, I had_10_ type errors, one was real. Can you guess 
what went wrong?

Next I had one logical error, which would have launched anti-aircraft 
rockets at anything remotely on the planet. (This is an excerpt from 
the Hudak-documented DoD programming contest, reformulated a in A 
Little Java for peaceful purposes :-)

Yes, I am on record saying that I'd use OCAML if I worked in industry, 
but boy this makes me reconsider this one.

-- Matthias