Data.Aeson with ForeignFunctionInterface in ghc

Question

我有以下Haskell代码：

{-# LANGUAGE OverloadedStrings, DeriveGeneric, DeriveAnyClass  #-}
module BoardToJSON where
import GHC.Generics
import Data.Aeson
import Data.Aeson.Text (encodeToLazyText)
import Data.Text
import Control.Applicative
import Control.Monad
import qualified Data.ByteString.Lazy as B
import GHC.Generics
import Data.Text.Lazy.IO as I
import Foreign.C.Types
import Foreign.C.String
import Data.Maybe
import Data.List
import Data.Ix
import Data.List
import Data.Maybe
--foreign export ccall writef :: IO ()
data Piece = Piece {
  _type :: !Text,
  _color :: !Text,
  _x :: Int,
  _y :: Int
  } deriving (Eq, Show, Generic, ToJSON, FromJSON)
piecesList::[Piece]
piecesList = [Piece "Rook" "White" 1 1, Piece "Knight" "White" 2 1, Piece "Bishop" "White" 3 1, Piece "Queen" "White" 4 1,
          Piece "King" "White" 5 1, Piece "Bishop" "White" 6 1, Piece "Knight" "White" 7 1, Piece "Rook" "White" 8 1,
          Piece "Pawn" "White" 1 2, Piece "Pawn" "White" 2 2, Piece "Pawn" "White" 3 2, Piece "Pawn" "White" 4 2,
          Piece "Pawn" "White" 5 2, Piece "Pawn" "White" 6 2, Piece "Pawn" "White" 7 2, Piece "Pawn" "White" 8 2,
          Piece "Rook" "Black" 1 8, Piece "Knight" "Black" 2 8, Piece "Bishop" "Black" 3 8, Piece "Queen" "Black" 4 8,
          Piece "King" "Black" 5 8, Piece "Bishop" "Black" 6 8, Piece "Knight" "Black" 7 8, Piece "Rook" "Black" 8 8,
          Piece "Pawn" "Black" 1 7, Piece "Pawn" "Black" 2 7, Piece "Pawn" "Black" 3 7, Piece "Pawn" "Black" 4 7,
          Piece "Pawn" "Black" 5 7, Piece "Pawn" "Black" 6 7, Piece "Pawn" "Black" 7 7, Piece "Pawn" "Black" 8 7]
jsonFile :: FilePath
jsonFile = "pieces.json"
writef = I.writeFile jsonFile (encodeToLazyText piecesList)
getJSON :: IO B.ByteString
getJSON = B.readFile jsonFile
getPieces :: IO (Either String [Piece])
getPieces = (eitherDecode <$> getJSON) :: IO (Either String [Piece])

aeson与阴谋集团一起安装。

做的时候：

$ ghci
Prelude> :load BoardToJSON
*BoardToJSON> writef

我正在编写一个包含片段数组的 Json 文件。

但是，当取消注释foreign export ccall writef :: IO ()并编译时：

CPP_SOURCES = main.cpp
HASKELL_SOURCES = haskell/BoardToJSON.hs
OBJECTS = haskell/*.o *.o
main: compileHaskell compileCPP link clean;
compileHaskell: $(HASKELL_SOURCES); ghc -c -XForeignFunctionInterface -fforce-recomp -O $(HASKELL_SOURCES)
compileCPP: $(CPP_SOURCES); g++ -c -I/usr/lib/ghc/include  -O $(CPP_SOURCES)
link: ; ghc -o Main -no-hs-main $(OBJECTS) -lstdc++
clean: ; rm -rf main && rm -rf haskell/*.o && rm *.o && rm -rf haskell/*.hi && rm -rf haskell/*_stub.h

compileHaskell和compileCPP运行良好，但我收到一堆类型的错误：

/tmp/ghca1ca_0/ghc_8.o:(.data.rel.ro+0x2a8): undefined reference to `bytestringzm0zi10zi8zi1_DataziByteStringziLazzy_getContents2_closure'
collect2: error: ld returned 1 exit status
`gcc' failed in phase `Linker'. (Exit code: 1)
makefile:12: recipe for target 'link' failed

我的猜测是 ghc 不知道在哪里可以找到aeson所以我做了：

$ sudo echo "/root/.cabal/lib/x86_64-linux-ghc-8.0.2" > /etc/ld.so.conf.d/x86_64-linux-gnu.conf
$ sudo ldconfig
$ sudo ldconfig -v | grep -i aeson                 
ldconfig: Path `/lib/x86_64-linux-gnu' given more than once
ldconfig: Path `/usr/lib/x86_64-linux-gnu' given more than once
ldconfig: /lib/x86_64-linux-gnu/ld-2.24.so is the dynamic linker, ignoring
libHSaeson-1.1.1.0-4sfmSwjYSZ4CJzSxs6L5hG-ghc8.0.1.so -> libHSaeson-1.1.1.0-4sfmSwjYSZ4CJzSxs6L5hG-ghc8.0.1.so

没有机会。

我尝试添加-llibHSaeson，-lHSaeson或-laeson来链接目标。但没有任何效果。

知道吗？

---

编辑

经过进一步的研究，我尝试重新安装 aeson 并--enable-shared

$ cabal install aeson --enable-shared --reinstall

同样的问题。

Answer 1

当您提供.o文件作为GHC的输入时，它不知道它们是否来自Haskell模块。因此，它无法知道需要链接哪些Haskell依赖项。

您可以在链接命令行上手动指定依赖项(例如 -package aeson(，或者在链接命令行上提供原始的Haskell模块，在这种情况下，GHC将自动确定依赖关系。