haskell - Get indices of Applicative Traversable without dummy -

-

let's have v, both applicative , traversable. how can v indices of v? concrete example, consider v3 linear. want v3 0 1 2.

one way use mapaccuml dummy, example:

snd $ t.mapaccuml      (\idx _ -> (idx + 1, idx))      0 (pure "") :: v3 int

but (pure "") dummy feels inelegant. how can in more elegant way?

you not going escape using pure if doing applicative , traversable. it's function in classes gives value of type without having one.

also, dummy determines shape of value construct. consider type such lists, not values have same shape: how choose between constructing [0], [0,1] or [0,1,2]? (a pure-based dummy gives first one.)


Comments

Post a Comment

Popular posts from this blog

java - Could not locate OpenAL library -

-
i writing game using slick2d library, uses lwjgl. lwjgl version 2.9.3. using netbeans 8. i tried adding sounds game, example music track on main menu. problem is, exception when run game, despite game still compiling , running except sound of course: sat mar 21 01:23:57 edt 2015 error:could not locate openal library. org.lwjgl.lwjglexception: not locate openal library. @ org.lwjgl.openal.al.create(al.java:156) @ org.lwjgl.openal.al.create(al.java:156) @ org.lwjgl.openal.al.create(al.java:102) @ org.lwjgl.openal.al.create(al.java:206) @ org.newdawn.slick.openal.soundstore$1.run(soundstore.java:295) @ java.security.accesscontroller.doprivileged(native method) @ org.newdawn.slick.openal.soundstore.init(soundstore.java:292) @ org.newdawn.slick.music.<init>(music.java:156) @ org.newdawn.slick.music.<init>(music.java:75) @ view.mainmenu.init(mainmenu.java:58) i didn't include rest of error states error happens in game code. the...
Read more

c++ - Delete matches in OpenCV (Keypoints and descriptors) -

-
i want check scene image against 2 train images. that, detect features , compute descriptors of both training images. before detecting, computing , matching scene image, delete matches of train1 , train2. because these matches won't facilitate matching of scene image train1 , train2. so, match train1 train2 , vector of matches trainidx , queryidx. how can delete these matches in keypoints-vector , descriptor matrix of train1 , train2? best regards, dwi i have done below: std::vector<cv::keypoint> keypoints[2]; cv::mat descriptor[2]; std::vector< cv::dmatch > matches; /* write code generate keypoints, descriptors , matches here... keypoint[0] -> train image 1 keypoints keypoint[1] -> train image 2 keypoints descriptor[0] -> train image 1 descriptors descriptor[1] -> train image 2 descriptors matches -> matched between train image 1 , 2 */ // logic keep unmatched keypoints , corresponding descriptor...
Read more

sorting - opencl Bitonic sort with 64 bits keys -

-
i used nvidia sdk bitonic sort , works great me. 32 bits (uint) need ulong keys. have typically 2^14 keys @ time , power of 2. searched on not find kernel designed ulong. i tried modified nvidia sdk bitonic sort using ulong keys not work. kernel not crash after de call clenqueuendrangekernel got error : cl_invalid_command_queue can tell me how modify bitonic sort or radixsort, or can sort ulong keys? i running nvidia quadro 4000 opencl 1.1 cuda 6.5.20 full_profile used original nvidia sdk bitonicsort.cl i used"ulong" keys , value input , ouput instead of "uint" thanks helping i made work-around suit need. used 30 bits of key , 18 high bits of value sorting. changed comparators (2 lines): '#define mask 0xffffc000 // suit need from this: if( (*keya > *keyb) == dir ) this: if(((*keya > *keyb)||((*keya == *keyb)&&((*vala & mask)> (*valb & mask)))) == dir ) it works fine. but, still, it's work-a...
Read more