我需要类似以下内容的东西:
-- Main.hs
module Main where
main :: IO ()
main = do
<import Plugin>
print Plugin.computation
有了像插件一样的东西
-- Plugin.hs
module Plugin where
computation :: Int
computation = 4
然而,我需要插件与主应用程序一起编译。它们需要一起部署。模块的导入(而不是编译)应该动态发生。
我在途中找到了Dynamically loading compiled Haskell module - GHC 7.6,它可以在GHC 8.0.2上正常工作,除了一个问题:执行应用程序时需要将插件的源文件放在当前工作目录中。
编辑(07.12.2017)
是否可能使用GHC API从字符串中加载模块而不是从文件中加载?http://hackage.haskell.org/package/ghc-8.2.1/docs/GHC.html#t:Target表明这是可能的,但是文档有很多漏洞,我找不到实现这一点的方法。如果可以实现这一点,我可以使用file-embed将插件源文件包含到编译后的二进制文件中。 例如:module Main where
-- Dynamic loading of modules
import GHC
import GHC.Paths ( libdir )
import DynFlags
import Unsafe.Coerce
import Data.Time.Clock (getCurrentTime)
import StringBuffer
pluginModuleNameStr :: String
pluginModuleNameStr = "MyPlugin"
pluginSourceStr :: String
pluginSourceStr = unlines
[ "module MyPlugin where"
, "computation :: Int"
, "computation = 4"
]
pluginModuleName :: ModuleName
pluginModuleName = mkModuleName pluginModuleNameStr
pluginSource :: StringBuffer
pluginSource = stringToStringBuffer pluginSourceStr
main :: IO ()
main = do
currentTime <- getCurrentTime
defaultErrorHandler defaultFatalMessager defaultFlushOut $ do
result <- runGhc (Just libdir) $ do
dflags <- getSessionDynFlags
setSessionDynFlags dflags
let target = Target { targetId = TargetModule $ pluginModuleName
, targetAllowObjCode = True
, targetContents = Just ( pluginSource
, currentTime
)
}
setTargets [target]
r <- load LoadAllTargets
case r of
Failed -> error "Compilation failed"
Succeeded -> do
setContext [IIDecl $ simpleImportDecl pluginModuleName]
result <- compileExpr ("MyPlugin.computation")
let result' = unsafeCoerce result :: Int
return result'
print result
然而,这会导致
<command-line>: panic! (the 'impossible' happened)
(GHC version 8.0.2 for x86_64-apple-darwin):
module ‘MyPlugin’ is a package module
编辑(2017年8月12日)
我可以通过将源代码写入临时文件并像链接的帖子中那样加载它来直接将“插件”编译到最终二进制文件中(动态加载已编译的Haskell模块-GHC 7.6)。然而,如果插件从Hackage导入包,则无法很好地运行:
module Main where
import Control.Monad.IO.Class (liftIO)
import DynFlags
import GHC
import GHC.Paths (libdir)
import System.Directory (getTemporaryDirectory, removePathForcibly)
import Unsafe.Coerce (unsafeCoerce)
pluginModuleNameStr :: String
pluginModuleNameStr = "MyPlugin"
pluginSourceStr :: String
pluginSourceStr = unlines
[ "module MyPlugin where"
, "import Data.Aeson"
, "computation :: Int"
, "computation = 4"
]
writeTempFile :: IO FilePath
writeTempFile = do
dir <- getTemporaryDirectory
let file = dir ++ "/" ++ pluginModuleNameStr ++ ".hs"
writeFile file pluginSourceStr
return file
main :: IO ()
main = do
moduleFile <- writeTempFile
defaultErrorHandler defaultFatalMessager defaultFlushOut $ do
result <- runGhc (Just libdir) $ do
dflags <- getSessionDynFlags
setSessionDynFlags dflags
target <- guessTarget moduleFile Nothing
setTargets [target]
r <- load LoadAllTargets
liftIO $ removePathForcibly moduleFile
case r of
Failed -> error "Compilation failed"
Succeeded -> do
setContext [IIDecl $ simpleImportDecl $ mkModuleName pluginModuleNameStr]
result <- compileExpr "MyPlugin.computation"
let result' = unsafeCoerce result :: Int
return result'
print result
有没有办法在插件中包含语句 import Data.Aeson
的情况下加载包?如果我将它添加到插件字符串中,它会失败。
/var/folders/t2/hp9y8x6s6rs7zg21hdzvhbf40000gn/T/MyPlugin.hs:2:1: error:
Failed to load interface for ‘Data.Aeson’
Perhaps you meant Data.Version (from base-4.9.1.0)
Use -v to see a list of the files searched for.
haskell-loader-exe: panic! (the 'impossible' happened)
(GHC version 8.0.2 for x86_64-apple-darwin):
Compilation failed
CallStack (from HasCallStack):
error, called at app/Main.hs:40:19 in main:Main
我请求的原因是数据库支持:我们使用Persistent访问数据库,需要动态导入来支持多个数据库(MySQL、PostgreSQL和SQLite),同时仍然允许最终用户只安装其中一个数据库服务器(换句话说:如果他们只使用PostgreSQL,则不要求用户安装所有这三个数据库)。当用户实际配置主应用程序使用该模块时,才应加载特定于数据库的模块。
如果我不import Database.Persist.MySQL
,那么应用程序不需要安装MySQL。否则,应用程序将失败,例如:
dyld: Library not loaded:
/usr/local/opt/mysql/lib/libmysqlclient.20.dylib
在 macOS 上。