小编lew*_*urm的帖子

我有一个关于在Haskell FFI和GHC的交互模式的问题再次.

考虑FFISo.hs:

{-# LANGUAGE OverloadedStrings #-}
module Main where

import qualified Data.ByteString.Char8 as B

import FFIFun.Foo

main :: IO ()
main = do
  B.putStrLn "main"
  callMeFromC
  callMeFromHaskell
  return ()

c.c:

#include <stdio.h>

void callMeFromC(void);

void callMeFromHaskell(void)
{
    printf("callMeFromHaskell\n");
    callMeFromC();
}

FFIFun/Foo.hs:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module FFIFun.Foo where

import qualified Data.ByteString.Char8 as B

foreign import ccall "callMeFromHaskell"
  callMeFromHaskell :: IO ()

foreign export ccall callMeFromC :: IO ()
callMeFromC …

关于Haskell中的FFI和GHC的交互模式我有一个问题.

(来源也可以通过要点获得):

FFISo.hs:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module Main where

import qualified Data.ByteString.Char8 as B

foreign import ccall "callMeFromHaskell"
  callMeFromHaskell :: IO ()

foreign export ccall callMeFromC :: IO ()
callMeFromC :: IO ()
callMeFromC = B.putStrLn "callMeFromC"

main :: IO ()
main = do
  B.putStrLn "main"
  callMeFromHaskell
  return ()

抄送:

#include <stdio.h>

void callMeFromC(void);

void callMeFromHaskell(void)
{   
    printf("callMeFromHaskell\n");
    callMeFromC();
}

Makefile文件:

GHC_OPT := -Wall -O2 -fno-warn-unused-do-bind

all: ffiso

test: ffiso
    ./$<

ffiso: FFISo.hs …

我哈巴狗10.04更新了我的显影机从Ubuntu的Ubuntu的LTS 12.04(或ghc 6.12.1到ghc 7.4.1)和我在均流项目碰到一个很奇怪的行为.

几个小时后,我把它减少到以下代码:

{-# LANGUAGE ForeignFunctionInterface #-}
module Main where

import Data.Word
import Text.Printf
import Foreign

foreign import ccall "dynamic"
   code_void :: FunPtr (IO ()) -> (IO ())

main :: IO ()
main = do
  entryPtr <- (mallocBytes 2)
  poke entryPtr (0xc390 :: Word16) -- nop (0x90); ret(0xc3) (little endian order)

  _ <- printf "entry point: 0x%08x\n" ((fromIntegral $ ptrToIntPtr entryPtr) :: Int)
  _ <- getLine -- for debugging
  code_void $ castPtrToFunPtr entryPtr
  putStrLn …

我实现了一个小函数bruteforce,使用惰性求值来找到问题的第一个有效解决方案:

import Data.Maybe

bruteforce :: (a -> Bool) -> [a] -> Maybe a
bruteforce f xs
  | null result = Nothing
  | otherwise = Just $ head result
  where
    result = mapMaybe bruteforce' xs
    -- test one instance
    bruteforce' x
      | f x = Just x
      | otherwise = Nothing

generatorString :: Int -> [String]
generatorString 0 = [""]
generatorString deep = concatMap (\x -> map (\ys -> (x:ys)) nextgen) ['a'..'z']
  where nextgen = generatorString (deep - 1) …

我想定义一个记录器功能，例如

myPutStrLn = putStrLn . (++) "log: "
main = do myPutStrLn "hello"

很好 现在，我想格式化与所提供的字符串printf，这样

myPutStrLn $ printf "test %d" (23 :: Int)

大！由于我经常使用这种模式，因此我想将其printf纳入记录器功能：

myPrintf = logger . printf
  where
    -- note, this is just an example. should be
    -- replaceable with any function with this
    -- typesignature
    logger :: String -> IO ()
    logger = putStrLn . (++) "log: "

main = myPrintf "test %d" (23 :: Int)

不幸的是，这失败了

The function `myPrintf' is applied to …

有一个相当低级别的应用程序,我进入一个sitatuion我需要确定Haskell函数的地址.我能用FFI做到这一点,就是C,但我想直接在Haskell中做到这一点.

这是我目前使用FFI的解决方案:

main.hs:

{-# LANGUAGE ForeignFunctionInterface #-}
module Main where

import Foreign
import Foreign.C.Types
import Text.Printf

foreign import ccall "getFuncAddr"
  getFuncAddr :: CULong

main :: IO ()
main = do
  printf "0x%016x\n" (fromIntegral getFuncAddr :: Word64)

foreign export ccall func :: IO ()
func :: IO ()
func = do
  printf "hello world\n"

ffi.c:

void func(void);

unsigned long getFuncAddr(void)
{
    return (unsigned long) func;
}

Makefile文件:

all: main
    ./$<
    objdump -D $< | grep '<func>'

main: main.hs ffi.c
    ghc --make …