我试图弄清楚基本的IO
Haskell 函数是定义好的,所以我使用了this reference我到了putChar
函数定义:
putChar :: Char -> IO ()
putChar = primPutChar
但是,现在我找不到关于此
primPutChar
的更多信息。随时随地发挥作用。也许它可能指的是预编译的函数,可作为共享对象的二进制文件?如果是这样,是否可以看到它的源代码?
最佳答案
什么prim*
方法
既然你是从报告的角度来问这个问题,那么我们也从报告的角度来回答这个问题:
Primitives that are not definable in Haskell , indicated by names starting with "
prim
", are defined in a system dependent manner in modulePreludeBuiltin
and are not shown here
这在 Haskell2010 by the way 中仍然相同。 .
它是如何在 GHC 中实现的
但是,您可以 have a look at
base
's source看看它是如何在 GHC 中实现的:putChar :: Char -> IO ()
putChar c = hPutChar stdout c
从那里你将深入兔子洞。
hPutChar
如何知道怎么打印东西吗?好吧,它没有。它仅“缓冲”并检查您是否可以编写:hPutChar :: Handle -> Char -> IO ()
hPutChar handle c = do
c `seq` return ()
wantWritableHandle "hPutChar" handle $ \ handle_ -> do
hPutcBuffered handle_ c
写作完成于
writeCharBuffer
它填充一个内部缓冲区,直到它被填满(或到达一行 - 它实际上取决于缓冲区模式):writeCharBuffer h_@Handle__{..} !cbuf = do
-- much code omitted, like buffering
bbuf'' <- Buffered.flushWriteBuffer haDevice bbuf'
-- more code omitted, like buffering
那么
flushWriteBuffer
在哪里?定义?它实际上是 stdout
的一部分:stdout :: Handle stdout = unsafePerformIO $ do setBinaryMode FD.stdout enc <- getLocaleEncoding mkHandle FD.stdout "<stdout>" WriteHandle True (Just enc) nativeNewlineMode{-translate newlines-} (Just stdHandleFinalizer) Nothing
stdout :: FD
stdout = stdFD 1
文件描述符(
FD
)是 BufferedIO
的一个实例:instance BufferedIO FD where
-- some code omitted
flushWriteBuffer fd buf = writeBuf' fd buf
和
writeBuf
使用 instance GHC.IO.Device.RawIO FD
's write
,最终 leads to :writeRawBufferPtr loc !fd buf off len | isNonBlocking fd = unsafe_write -- unsafe is ok, it can't block | otherwise = do r <- unsafe_fdReady (fdFD fd) 1 0 0 if r /= 0 then write else do threadWaitWrite (fromIntegral (fdFD fd)); write where do_write call = fromIntegral `fmap` throwErrnoIfMinus1RetryMayBlock loc call (threadWaitWrite (fromIntegral (fdFD fd))) write = if threaded then safe_write else unsafe_write unsafe_write = do_write (c_write (fdFD fd) (buf `plusPtr` off) len) safe_write = do_write (c_safe_write (fdFD fd) (buf `plusPtr` off) len)
where we can see c_safe_write
and c_write
, which are usually bindings to C library functions:
foreign import capi unsafe "HsBase.h write"
c_write :: CInt -> Ptr Word8 -> CSize -> IO CSsize
所以,
putChar
使用 write
.至少在 GHC 的实现中。然而,该报告不需要该实现,因此允许另一个编译器/运行时使用其他功能。TL;博士
GHC 的实现使用
write
使用内部缓冲区来写入内容,包括单个字符。
关于Haskell primPutChar 定义,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34492110/