我对Haskell还是陌生的，我现在正在尝试在Haskell中用“ foldl any”实现“ elem”，但是它不起作用。
我的任意一个：
ffmpeg version n4.0-39-gda39990 Copyright (c) 2000-2018 the FFmpeg developers
built with gcc 4.9.x (GCC) 20150123 (prerelease)
configuration: --target-os=linux --cross-prefix=/root/bravobit/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi- --arch=arm --cpu=cortex-a8 --enable-runtime-cpudetect --sysroot=/root/bravobit/ffmpeg-android/toolchain-android/sysroot --enable-pic --enable-libx264 --enable-ffprobe --enable-libopus --enable-libvorbis --enable-libfdk-aac --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-fontconfig --enable-libvpx --enable-libass --enable-yasm --enable-pthreads --disable-debug --enable-version3 --enable-hardcoded-tables --disable-ffplay --disable-linux-perf --disable-doc --disable-shared --enable-static --enable-runtime-cpudetect --enable-nonfree --enable-network --enable-avresample --enable-avformat --enable-avcodec --enable-indev=lavfi --enable-hwaccels --enable-ffmpeg --enable-zlib --enable-gpl --enable-small --enable-nonfree --pkg-config=pkg-config --pkg-config-flags=--static --prefix=/root/bravobit/ffmpeg-android/build/armeabi-v7a --extra-cflags='-I/root/bravobit/ffmpeg-android/toolchain-android/include -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fno-strict-overflow -fstack-protector-all' --extra-ldflags='-L/root/bravobit/ffmpeg-android/toolchain-android/lib -Wl,-z,relro -Wl,-z,now -pie' --extra-cxxflags=
libavutil 56. 14.100 / 56. 14.100
libavcodec 58. 18.100 / 58. 18.100
libavformat 58. 12.100 / 58. 12.100
libavdevice 58. 3.100 / 58. 3.100
libavfilter 7. 16.100 / 7. 16.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 1.100 / 5. 1.100
libswresample 3. 1.100 / 3. 1.100
libpostproc 55. 1.100 / 55. 1.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/storage/emulated/0/Android/data/com.my.package/files/CameraTemp/2020_05_24_09_17_53.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
creation_time : 2020-05-24T08:18:02.000000Z
Duration: 00:00:01.64, start: 0.000000, bitrate: 20750 kb/s
Stream #0:0(eng): Video: h264 (avc1 / 0x31637661), yuv420p, 1920x1080, 18056 kb/s, SAR 1:1 DAR 16:9, 29.70 fps, 29.67 tbr, 90k tbn, 180k tbc (default)
Metadata:
creation_time : 2020-05-24T08:18:02.000000Z
handler_name : VideoHandle
Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 155 kb/s (default)
Metadata:
creation_time : 2020-05-24T08:18:02.000000Z
handler_name : SoundHandle
Input #1, png_pipe, from '/storage/emulated/0/Android/data/com.my.package/files/MyVideos/tempShapes.png':
Duration: N/A, bitrate: N/A
Stream #1:0: Video: png, rgba(pc), 1920x1128, 25 tbr, 25 tbn, 25 tbc
Stream mapping:
Stream #0:0 (h264) -> scale (graph 0)
Stream #1:0 (png) -> scale2ref:default (graph 0)
overlay (graph 0) -> Stream #0:0 (libx264)
Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
frame= 0 fps=0.0 q=0.0 size= 0kB time=-577014:32:22.77 bitrate= -0.0kbits/s speed=N/A
frame= 0 fps=0.0 q=0.0 size= 0kB time=-577014:32:22.77 bitrate= -0.0kbits/s speed=N/A
[libx264 @ 0xb83fc8a0] using SAR=1/1
[libx264 @ 0xb83fc8a0] using cpu capabilities: ARMv6 NEON
[libx264 @ 0xb83fc8a0] profile Constrained Baseline, level 4.2
[libx264 @ 0xb83fc8a0] 264 - core 152 r2851M ba24899 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=2 keyint_min=1 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
Output #0, mp4, to '/storage/emulated/0/Android/data/com.my.package/files/MyVideos/video with line.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
encoder : Lavf58.12.100
Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 1920x1128 [SAR 1:1 DAR 80:47], q=-1--1, 29 fps, 14848 tbn, 29 tbc (default)
Metadata:
encoder : Lavc58.18.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
creation_time : 2020-05-24T08:18:02.000000Z
handler_name : SoundHandle
encoder : Lavc58.18.100 aac
frame= 1 fps=0.4 q=0.0 size= 0kB time=00:00:01.01 bitrate= 0.4kbits/s speed=0.397x
frame= 5 fps=1.6 q=0.0 size= 0kB time=00:00:01.01 bitrate= 0.4kbits/s speed=0.33x
frame= 9 fps=2.5 q=24.0 size= 256kB time=00:00:01.01 bitrate=2075.0kbits/s speed=0.28x
frame= 13 fps=3.1 q=25.0 size= 1024kB time=00:00:01.01 bitrate=8298.9kbits/s speed=0.243x
frame= 18 fps=3.8 q=29.0 size= 2048kB time=00:00:01.01 bitrate=16597.5kbits/s speed=0.214x
frame= 21 fps=3.9 q=25.0 size= 2560kB time=00:00:01.01 bitrate=20746.7kbits/s speed=0.19x
frame= 23 fps=3.9 q=25.0 size= 2816kB time=00:00:01.01 bitrate=22821.4kbits/s speed=0.173x
frame= 26 fps=4.0 q=29.0 size= 3584kB time=00:00:01.01 bitrate=29045.3kbits/s speed=0.156x
Past duration 0.617577 too large
Past duration 0.639641 too large
frame= 28 fps=3.9 q=29.0 size= 3840kB time=00:00:01.01 bitrate=31119.9kbits/s speed=0.142x
Past duration 0.665230 too large
frame= 29 fps=3.8 q=25.0 size= 3840kB time=00:00:01.01 bitrate=31119.9kbits/s speed=0.132x
Past duration 0.690834 too large
Past duration 0.711281 too large
Past duration 0.736885 too large
frame= 32 fps=3.9 q=29.0 size= 4608kB time=00:00:01.01 bitrate=37343.8kbits/s speed=0.123x
Past duration 0.762474 too large
Past duration 0.783577 too large
Past duration 0.807564 too large
frame= 35 fps=3.9 q=25.0 size= 4864kB time=00:00:01.01 bitrate=39418.4kbits/s speed=0.112x
Past duration 0.831551 too large
Past duration 0.855537 too large
frame= 37 fps=3.5 q=25.0 size= 5376kB time=00:00:01.01 bitrate=43567.7kbits/s speed=0.0968x
Past duration 0.879524 too large
Past duration 0.903511 too large
frame= 39 fps=3.4 q=25.0 size= 5376kB time=00:00:01.06 bitrate=41196.6kbits/s speed=0.0927x
Past duration 0.927498 too large
Past duration 0.951500 too large
frame= 41 fps=3.4 q=25.0 size= 5376kB time=00:00:01.13 bitrate=38700.0kbits/s speed=0.0931x
frame= 41 fps=3.2 q=25.0 size= 5376kB time=00:00:01.13 bitrate=38700.0kbits/s speed=0.0886x
frame= 41 fps=3.1 q=25.0 size= 5888kB time=00:00:01.43 bitrate=33554.2kbits/s speed=0.108x
Past duration 0.975487 too large
frame= 45 fps=3.2 q=26.0 size= 6656kB time=00:00:01.60 bitrate=33905.4kbits/s speed=0.114x
frame= 45 fps=3.0 q=-1.0 Lsize= 8158kB time=00:00:01.65 bitrate=40480.7kbits/s speed=0.11x
video:8127kB audio:28kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.032895%
[libx264 @ 0xb83fc8a0] frame I:23 Avg QP:24.70 size:337646
[libx264 @ 0xb83fc8a0] frame P:22 Avg QP:29.00 size: 25250
[libx264 @ 0xb83fc8a0] mb I I16..4: 100.0% 0.0% 0.0%
[libx264 @ 0xb83fc8a0] mb P I16..4: 0.4% 0.0% 0.0% P16..4: 43.6% 0.0% 0.0% 0.0% 0.0% skip:56.0%
[libx264 @ 0xb83fc8a0] coded y,uvDC,uvAC intra: 90.0% 84.7% 58.1% inter: 20.1% 6.2% 0.1%
[libx264 @ 0xb83fc8a0] i16 v,h,dc,p: 25% 28% 28% 20%
[libx264 @ 0xb83fc8a0] i8c dc,h,v,p: 39% 25% 20% 16%
[libx264 @ 0xb83fc8a0] kb/s:42901.20
[aac @ 0xb83d7d10] Qavg: 3517.779
这是我的元素：
any' p = foldl' (\y x -> p x || y) False
我的第一次尝试是：
elem' y = foldl' (\z x -> x==y || z) False
但是我每次都会出错
答案 0 :(得分：2)
您的elemfa :: Foldable f => (a -> Bool) -> f a -> Bool使用了any''''，但该功能不存在。如果您将其重写为：
elemfa :: Foldable f => (a -> Bool) -> f a -> Bool
elemfa p y = not (any' (\x -> not (p x)) y)您可以使用以下方法使其更干净：
elemfa :: Foldable f => (a -> Bool) -> f a -> Bool
elemfa p = not . any' (not . p)它将至少产生输出。此函数将检查所有元素是否满足给定谓词。
话虽这么说，在此处foldl，any和elem中使用elemfa并不理想，因为这意味着它将不断在列表中进行迭代，即使找到满足该谓词的元素。因此，如果您使用无限列表，则即使找到了元素，它也不会返回True：
Prelude Data.List> elem' 1 (1 : repeat 2)
… keeps looking …在找到元素后，foldr :: Foldable f => (a -> b -> b) -> b -> f a -> b可用于停止搜索，例如：
any' :: Foldable f => (a -> Bool) -> f a -> Bool
any' p = foldr (\x -> (p x ||)) False
elem' :: (Foldable f, Eq a) => a -> f a -> Bool
elem' x = any' (x==)
all' :: Foldable f => (a -> Bool) -> f a -> Bool
all' p = not . any (not . p)