我尝试使用if(isset($_SERVER["Authorization"]) && $_SERVER["Authorization"] == '2d30ff242f8650954bfe8c993f084f4f'){
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}
函数在Haskell中创建using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Threading.Tasks;
/// <summary>
/// Creates a GIF using .Net GIF encoding and additional animation headers.
/// </summary>
public class GifWriter : IDisposable
{
#region Fields
const long SourceGlobalColorInfoPosition = 10,
SourceImageBlockPosition = 789;
readonly BinaryWriter _writer;
bool _firstFrame = true;
readonly object _syncLock = new object();
#endregion
/// <summary>
/// Creates a new instance of GifWriter.
/// </summary>
/// <param name="OutStream">The <see cref="Stream"/> to output the Gif to.</param>
/// <param name="DefaultFrameDelay">Default Delay between consecutive frames... FrameRate = 1000 / DefaultFrameDelay.</param>
/// <param name="Repeat">No of times the Gif should repeat... -1 to repeat indefinitely.</param>
public GifWriter(Stream OutStream, int DefaultFrameDelay = 500, int Repeat = -1)
{
if (OutStream == null)
throw new ArgumentNullException(nameof(OutStream));
if (DefaultFrameDelay <= 0)
throw new ArgumentOutOfRangeException(nameof(DefaultFrameDelay));
if (Repeat < -1)
throw new ArgumentOutOfRangeException(nameof(Repeat));
_writer = new BinaryWriter(OutStream);
this.DefaultFrameDelay = DefaultFrameDelay;
this.Repeat = Repeat;
}
/// <summary>
/// Creates a new instance of GifWriter.
/// </summary>
/// <param name="FileName">The path to the file to output the Gif to.</param>
/// <param name="DefaultFrameDelay">Default Delay between consecutive frames... FrameRate = 1000 / DefaultFrameDelay.</param>
/// <param name="Repeat">No of times the Gif should repeat... -1 to repeat indefinitely.</param>
public GifWriter(string FileName, int DefaultFrameDelay = 500, int Repeat = -1)
: this(new FileStream(FileName, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read), DefaultFrameDelay, Repeat) { }
#region Properties
/// <summary>
/// Gets or Sets the Default Width of a Frame. Used when unspecified.
/// </summary>
public int DefaultWidth { get; set; }
/// <summary>
/// Gets or Sets the Default Height of a Frame. Used when unspecified.
/// </summary>
public int DefaultHeight { get; set; }
/// <summary>
/// Gets or Sets the Default Delay in Milliseconds.
/// </summary>
public int DefaultFrameDelay { get; set; }
/// <summary>
/// The Number of Times the Animation must repeat.
/// -1 indicates no repeat. 0 indicates repeat indefinitely
/// </summary>
public int Repeat { get; }
#endregion
/// <summary>
/// Adds a frame to this animation.
/// </summary>
/// <param name="Image">The image to add</param>
/// <param name="Delay">Delay in Milliseconds between this and last frame... 0 = <see cref="DefaultFrameDelay"/></param>
public void WriteFrame(Image Image, int Delay = 0)
{
lock (_syncLock)
using (var gifStream = new MemoryStream())
{
Image.Save(gifStream, ImageFormat.Gif);
// Steal the global color table info
if (_firstFrame)
InitHeader(gifStream, _writer, Image.Width, Image.Height);
WriteGraphicControlBlock(gifStream, _writer, Delay == 0 ? DefaultFrameDelay : Delay);
WriteImageBlock(gifStream, _writer, !_firstFrame, 0, 0, Image.Width, Image.Height);
}
if (_firstFrame)
_firstFrame = false;
}
#region Write
void InitHeader(Stream SourceGif, BinaryWriter Writer, int Width, int Height)
{
// File Header
Writer.Write("GIF".ToCharArray()); // File type
Writer.Write("89a".ToCharArray()); // File Version
Writer.Write((short)(DefaultWidth == 0 ? Width : DefaultWidth)); // Initial Logical Width
Writer.Write((short)(DefaultHeight == 0 ? Height : DefaultHeight)); // Initial Logical Height
SourceGif.Position = SourceGlobalColorInfoPosition;
Writer.Write((byte)SourceGif.ReadByte()); // Global Color Table Info
Writer.Write((byte)0); // Background Color Index
Writer.Write((byte)0); // Pixel aspect ratio
WriteColorTable(SourceGif, Writer);
// App Extension Header for Repeating
if (Repeat == -1)
return;
Writer.Write(unchecked((short)0xff21)); // Application Extension Block Identifier
Writer.Write((byte)0x0b); // Application Block Size
Writer.Write("NETSCAPE2.0".ToCharArray()); // Application Identifier
Writer.Write((byte)3); // Application block length
Writer.Write((byte)1);
Writer.Write((short)Repeat); // Repeat count for images.
Writer.Write((byte)0); // terminator
}
static void WriteColorTable(Stream SourceGif, BinaryWriter Writer)
{
SourceGif.Position = 13; // Locating the image color table
var colorTable = new byte[768];
SourceGif.Read(colorTable, 0, colorTable.Length);
Writer.Write(colorTable, 0, colorTable.Length);
}
static void WriteGraphicControlBlock(Stream SourceGif, BinaryWriter Writer, int FrameDelay)
{
SourceGif.Position = 781; // Locating the source GCE
var blockhead = new byte[8];
SourceGif.Read(blockhead, 0, blockhead.Length); // Reading source GCE
Writer.Write(unchecked((short)0xf921)); // Identifier
Writer.Write((byte)0x04); // Block Size
Writer.Write((byte)(blockhead[3] & 0xf7 | 0x08)); // Setting disposal flag
Writer.Write((short)(FrameDelay / 10)); // Setting frame delay
Writer.Write(blockhead[6]); // Transparent color index
Writer.Write((byte)0); // Terminator
}
static void WriteImageBlock(Stream SourceGif, BinaryWriter Writer, bool IncludeColorTable, int X, int Y, int Width, int Height)
{
SourceGif.Position = SourceImageBlockPosition; // Locating the image block
var header = new byte[11];
SourceGif.Read(header, 0, header.Length);
Writer.Write(header[0]); // Separator
Writer.Write((short)X); // Position X
Writer.Write((short)Y); // Position Y
Writer.Write((short)Width); // Width
Writer.Write((short)Height); // Height
if (IncludeColorTable) // If first frame, use global color table - else use local
{
SourceGif.Position = SourceGlobalColorInfoPosition;
Writer.Write((byte)(SourceGif.ReadByte() & 0x3f | 0x80)); // Enabling local color table
WriteColorTable(SourceGif, Writer);
}
else Writer.Write((byte)(header[9] & 0x07 | 0x07)); // Disabling local color table
Writer.Write(header[10]); // LZW Min Code Size
// Read/Write image data
SourceGif.Position = SourceImageBlockPosition + header.Length;
var dataLength = SourceGif.ReadByte();
while (dataLength > 0)
{
var imgData = new byte[dataLength];
SourceGif.Read(imgData, 0, dataLength);
Writer.Write((byte)dataLength);
Writer.Write(imgData, 0, dataLength);
dataLength = SourceGif.ReadByte();
}
Writer.Write((byte)0); // Terminator
}
#endregion
/// <summary>
/// Frees all resources used by this object.
/// </summary>
public void Dispose()
{
// Complete File
_writer.Write((byte)0x3b); // File Trailer
_writer.BaseStream.Dispose();
_writer.Dispose();
}
}
函数的新实现。
到目前为止，我有这个：
elem foldr函数使用count :: Eq a => a -> [a] -> Integer
count x (y:ys) = foldl (\counter y -> if y == x then counter + 1 else counter) 0 ys
count _ [] = 0
elem' :: Eq a => a -> [a] -> Bool
elem' x (y:ys) = foldr (\i elem-> if (count x (y:ys)) > 0 then True else False) False ys
elem' _ [] = False
计算x（我写的另一个函数）的出现次数。这适用于有限列表，但问题是我想利用无限列表的count惰性计算。如果我尝试使用无限列表作为输入，程序将永远挂起。
基本上我想＆＃34;突破＆＃34;一旦我在列表中找到x的任何实例并返回true，否则返回false。
感谢您的帮助。
答案 0 :(得分：2)
让我们从foldr模式的基本骨架开始：
elem :: Eq a => [a] -> Bool
elem x xs = foldr kons knil xs
当foldr看到[]时，它会返回knil。由于什么都不是空列表的元素，我们得出结论
knil = False
当foldr kons False看到列表a : as时，它会返回kons a (foldr kons False as)。我们可以归纳为foldr kons False as = elem x as，因此我们寻求在
kons
elem x (a : as) = kons a (elem x as)
我打赌你可以通过提出kons的定义来完成。注意布尔短路行为，以提高效率并避免无限列表出现问题。