我需要像
这样的东西-- Main.hs
module Main where
main :: IO ()
main = do
<import Plugin>
print Plugin.computation
使用插件
-- Plugin.hs
module Plugin where
computation :: Int
computation = 4
但是,我需要将插件与主应用程序一起编译。他们需要一起部署。只有模块的导入(而不是编译)才能动态发生。
我一路上找到了Dynamically loading compiled Haskell module - GHC 7.6,它在GHC 8.0.2中运行得很好,除了它在执行应用程序时需要插件的源文件在当前工作目录中。
是否可以使用GHC API从String而不是文件加载模块? http://hackage.haskell.org/package/ghc-8.2.1/docs/GHC.html#t:Target表明这是可能的,但文档有很多漏洞,我找不到实际执行此操作的方法。如果可以实现,我可以使用file-embed将插件源文件包含到已编译的二进制文件中。 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
我可以通过将源代码写入临时文件然后像链接的帖子(Dynamically loading compiled Haskell module - GHC 7.6)一样加载它,将“插件”直接编译成最终的二进制文件。但是,如果插件从Hackage中导入包,这种方法就不会很好:
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
例如,当MyPlugin
包含语句import Data.Aeson
时,有没有办法加载包?如果我将它添加到插件字符串,它将失败
/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
我的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三个数据库中的一个服务器(换句话说:如果用户只使用PostgreSQL,则不要求用户安装所有服务器)。只有在用户实际配置主应用程序才能使用该模块时,才应加载特定于数据库的模块。
如果我没有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。
答案 0 :(得分:1)
具有匹配模块名称的文件必须具有匹配的外观 - 它似乎与文件的内容无关。
在Linux上,我甚至可以将它作为/ dev / null的符号链接,但事情可行,但符号链接本身并不是。