[PRL] annoying types ARGH! -> structure-shy

[Matthias Felleisen]

Karl, please send out at least as much functionality as I did so people 
can compare.

On May 12, 2005, at 10:08 AM, Karl Lieberherr wrote:

> Here is my partial program that I wrote for Matthias for the same "free
> variable-like problem" that Matthias solved.
>
> class Compound {
> int countHits(final Point p) {
>    Integer res = (Integer)
>    Main.cg.traverse(this,"from Compound to Simple", new Visitor(){
>         int containedIn;
>         public void start() {containedIn = 0;}
>         public void before(Simple host){if (host.contains(p))
> containedIn++ ;};
>         public Object getReturnValue() {return new
> Integer(containedIn);}
>    });
>    return res.intValue();
> };
> }
>
> class Simple {
> boolean contains(Point p) {
>   return true;
>      }
> }
>
> Here is a sample input
>
> (
>   ( rectangle length 7 width 9 ref 3 4
>     circle radius 9 ref 6 7)
>   ( circle radius 10 ref 8 3
>     rectangle length 4 width 6 ref 5 1 )
> )
>
> And the point is that the details of the data model are not important,
> BOTH to the program and to the test input.
>
> Consider this class dictionary:
>
> Compound = "(" <first> Shape <second> Shape ")".
> Shape : Simple | Compound.
> Simple : Rectangle | Circle common "ref" Point.
> Rectangle = "rectangle" "length" <length> int "width" <width> int.
> Circle = "circle" "radius" <radius> int.
>
> Point = <x> int <y> int.
>
> Both program and test cases also work for this class dictionary:
>
> Compound = "(" <elements> List(Shape) ")".
> Shape : Simple | Compound.
> Simple : Rectangle | Circle common "ref" Point.
> Rectangle = "rectangle" "length" <length> int "width" <width> int.
> Circle = "circle" "radius" <radius> int.
>
> Point = <x> int <y> int.
> List(S) ~ {S}.
>
> Matthias solution does not have this flexibility.
>
> -- Karl
>
>
>> -----Original Message-----
>> From: prl-bounces at lists.ccs.neu.edu
> [mailto:prl-bounces at lists.ccs.neu.edu]
>> On Behalf Of Matthias Felleisen
>> Sent: Thursday, September 01, 2005 9:43 AM
>> To: PRL Mailing List
>> Subject: [PRL] annoying types ARGH!
>>
>> 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
>>
>>
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>