如何在Haskell中打印列表的内存地址

I'm studying how some programming languages assign memory to structured data (in this case I'm studying arrays).

我正在研究一些编程语言如何为结构化数据分配内存（在这种情况下我正在研究数组）。

I'm creating the array as shown here on section 3.

我正在创建数组，如第3节所示。

import Data.Array.IO
arr <- newArray (1,10) 37 :: IO (IOArray Int Int) --Sets default to 37

And what I'm trying to do is print each element's memory address, something like this:

我要做的是打印每个元素的内存地址，如下所示：

Array Start: <dec addr> | <hex addr> --Shows where the array itself is
Array 1: <dec addr> | <hex addr> --Memory address of the first element
Array 2: <dec addr> | <hex addr| --Memory address of the second element

The problem that I have is that I don't know how to get the memory address value for an element in Haskell.

我遇到的问题是我不知道如何获取Haskell中元素的内存地址值。

Is there a function similar to Python's id(object) or Ruby's object.object_id?

是否有类似于Python的id（对象）或Ruby的object.object_id的函数？

1 个解决方案

#1

You can use the following snippet which I borrowed from the ghc-heap-view package (it also contains an alternative solution using foreign import prim):

您可以使用我从ghc-heap-view包中借用的以下代码段（它还包含使用外部import prim的替代解决方案）：

{-# LANGUAGE MagicHash, BangPatterns #-}

import GHC.Exts

-- A datatype that has the same layout as Word and so can be casted to it.
data Ptr' a = Ptr' a

-- Any is a type to which any type can be safely unsafeCoerced to.
aToWord# :: Any -> Word#
aToWord# a = let !mb = Ptr' a in case unsafeCoerce# mb :: Word of W# addr -> addr

unsafeAddr :: a -> Int
unsafeAddr a = I# (word2Int# (aToWord# (unsafeCoerce# a)))

This works by first wrapping a inside a Ptr' constructor and then casting Ptr' a to Word. Since the a field is represented as a pointer, the resulting word now contains the address of the object. The usual caveats apply: this is unsafe, GHC-specific, breaks referential transparency, etc.

这是通过首先在Ptr'构造函数内部包装然后将Ptr'a转换为Word来实现的。由于a字段表示为指针，因此结果字现在包含对象的地址。通常的警告适用：这是不安全的，GHC特定的，打破参考透明度等。

Testing:

测试：

main :: IO ()
main = do
  arr <- newListArray (1,10) [1,2..] :: IO (IOArray Int Int)
  a1  <- readArray arr 1
  a2  <- readArray arr 2
  a1' <- readArray arr 1

  putStrLn $ "a1 : " ++ (show . unsafeAddr $! a1)
  putStrLn $ "a1 : " ++ (show . unsafeAddr $! a1)
  putStrLn $ "a2 : " ++ (show . unsafeAddr $! a2)
  putStrLn $ "a2 : " ++ (show . unsafeAddr $! a2)
  putStrLn $ "a1': " ++ (show . unsafeAddr $! a1')

Output:

输出：

a1 : 16785657
a1 : 16785657
a2 : 16785709
a2 : 16785709
a1': 16785657

Note that you should use unsafeAddr with $!, otherwise you'll be getting an address of a thunk that will evaluate to a instead of the a object itself:

请注意，您应该将unsafeAddr与$！一起使用，否则您将获得将评估为a而不是对象本身的thunk的地址：

  let a = 1
      b = 2
      c = a + b

  putStrLn $ "c: " ++ (show . unsafeAddr $ c)
  putStrLn $ "c: " ++ (show . unsafeAddr $! c)
  putStrLn $ "c: " ++ (show . unsafeAddr $! c)

Output:

输出：

c: 9465024
c: 9467001
c: 9467001