Read Java method signatures from haskell

JavaSig.hs

{-# LANGUAGE OverloadedStrings, FlexibleContexts #-}

import Control.Monad.Exception
import qualified Data.ByteString.Lazy as B
import Data.ByteString.Lazy.Char8 (pack)
import System.Environment (getArgs)

import JVM.ClassFile
import JVM.Assembler
import JVM.Builder
import JVM.Exceptions
import Java.ClassPath

args :: MethodSignature -> [ArgumentSignature]
args (MethodSignature a _) = a

ret :: MethodSignature -> ReturnSignature
ret (MethodSignature _ r) = r

copy :: (Throws ENotFound e, Throws ENotLoaded e, Throws UnexpectedEndMethod e) =>
       String -> B.ByteString -> GenerateIO e ()
copy klass meth = do
  -- Add current directory (with Hello.class) to ClassPath
  withClassPath $ addDirectory "."

  -- Load method signature: Hello.hello() from Hello.class
  helloJava <- getClassMethod klass meth

  let sig = ntSignature helloJava
  --newMethod [ACC_PUBLIC, ACC_STATIC] "hello" [undefined] (undefined) $ do
  newMethod [ACC_PUBLIC, ACC_STATIC] meth (args sig) (ret sig) $ do
    setStackSize 1
    
    i0 RETURN

  return ()

printSig :: String -> String -> IO ()
printSig klass meth = do
  copiedClass <- generateIO [] "Test" (copy ("./" ++ klass) (pack meth))
  let methSig = methodSignature $ head $ classMethods $ copiedClass
  putStrLn $ "Args: " ++ (show $ args methSig)
  putStrLn $ "Returns: " ++ (show $ ret methSig)
  

main :: IO ()
main = do
  argv <- getArgs
  case argv of
    [klass, meth] -> printSig klass meth
    _ -> putStrLn "Usage: JavaSig className methodName"