Re: How to model a rectangle?
Looks interesting, thanks! On Thu, Mar 5, 2015 at 4:43 PM, Leon Grapenthin wrote: > (defn rect2 [x y width height] > (let [lr [(+ width x) (+ width y)]] > (reify Rect > (upper-left [_] [x y]) > (lower-right [_] lr) > (area [_] (* width height) Just a quick remark: In JavaScript I purposefully did not use `width` and `height` for calculating area. That way the garbage collector can release them, making objects smaller. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: How to model a rectangle?
You could use Clojure protocols.
(defprotocol Rect
(upper-left [this])
(lower-right [this])
(area [this]))
(defn rect1 [x y width height]
(reify Rect
(upper-left [_] [x y])
(lower-right [_] [ (+ width x) (+ width y)])
(area [_] (* width height
(defn rect2 [x y width height]
(let [lr [(+ width x) (+ width y)]]
(reify Rect
(upper-left [_] [x y])
(lower-right [_] lr)
(area [_] (* width height)
On Thursday, March 5, 2015 at 4:48:11 PM UTC+1, Felix E. Klee wrote:
>
> Disclaimer: I’ve never done *any* Clojure programming, but I’m curious.
>
> Here’s how I may model an on-screen rectangle in JavaScript, a classless
> object oriented language:
>
> let createRectangle = function (x, y, width, height) {
> return {
> get upperLeft() {
> return [x, y];
> },
> get lowerRight() {
> return [x + width, y + height];
> },
> get area() {
> return width * height;
> }
> };
> };
>
> let r = createRectangle(0, 0, 50, 20);
> let s = createRectangle(10, 20, 40, 5);
> console.log(r.upperLeft, r.lowerRight, r.area);
> console.log(s.upperLeft, s.lowerRight, s.area);
>
> Now I run the profiler. I discover that in the inner loop of my program
> there are lots of calls needing the upper left and the lower right
> coordinates. So I change the inner workings of the object to store these
> instead:
>
> let createRectangle = function (x, y, width, height) {
> let upperLeft = [x, y], lowerRight = [x + width, y + height];
>
> return {
> get upperLeft() {
> return upperLeft;
> },
> get lowerRight() {
> return lowerRight;
> },
> get area() {
> return (lowerRight[0] - upperLeft[0]) *
> (lowerRight[1] - upperLeft[1]);
> }
> };
> };
>
> Boom: Now the program is twice as fast, and - what gives me great
> comfort - I know that this change breaks nothing. I only had to edit the
> code in *one* module. I didn’t need to think too much about efficiency
> of data structures in the beginning. I could just start going, then
> optimize in the end.
>
> *Can I program in a similar way using Clojure?*
>
--
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How to model a rectangle?
Disclaimer: I’ve never done *any* Clojure programming, but I’m curious.
Here’s how I may model an on-screen rectangle in JavaScript, a classless
object oriented language:
let createRectangle = function (x, y, width, height) {
return {
get upperLeft() {
return [x, y];
},
get lowerRight() {
return [x + width, y + height];
},
get area() {
return width * height;
}
};
};
let r = createRectangle(0, 0, 50, 20);
let s = createRectangle(10, 20, 40, 5);
console.log(r.upperLeft, r.lowerRight, r.area);
console.log(s.upperLeft, s.lowerRight, s.area);
Now I run the profiler. I discover that in the inner loop of my program
there are lots of calls needing the upper left and the lower right
coordinates. So I change the inner workings of the object to store these
instead:
let createRectangle = function (x, y, width, height) {
let upperLeft = [x, y], lowerRight = [x + width, y + height];
return {
get upperLeft() {
return upperLeft;
},
get lowerRight() {
return lowerRight;
},
get area() {
return (lowerRight[0] - upperLeft[0]) *
(lowerRight[1] - upperLeft[1]);
}
};
};
Boom: Now the program is twice as fast, and - what gives me great
comfort - I know that this change breaks nothing. I only had to edit the
code in *one* module. I didn’t need to think too much about efficiency
of data structures in the beginning. I could just start going, then
optimize in the end.
*Can I program in a similar way using Clojure?*
--
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