Fix a segmentation fault with Python 3.10.1

Problem: After upgrading to Python 3.10.1 and reinstalling PtGhci, I
started getting segfaults on initialization.

Solution: According to a note in
https://docs.python.org/3/c-api/init.html#before-python-initialization,
`Py_GetPath` should not be called before `Py_Initialize`, but PtGhci
does so anyway. The solution is simply to print debugging info after
Python is initialized.

I also removed some extraneous whitespace I found in Main while
debugging this.

app/Main.hs

@@ -1,4 +1,3 @@
-
 module Main where
 
 import Foreign.C.Types
@@ -29,7 +28,6 @@ main = do
   lookupEnv "PTGHCI_ENGINE_MODE" >>= \case
     Just _ -> runEngineMode env sockets
     Nothing -> runPythonInProc env sockets
-
 
 -- | The normal way we run -- Python interpreter runs prompt-toolkit loop
 -- in-process.
@@ -50,10 +48,9 @@ runPythonInProc env sockets = do
 runEngineMode :: Env -> Sockets -> IO ()
 runEngineMode env sockets = do
   sockAddrs <- socketEndpoints sockets
-  
+
   -- Print the socket addresses so Python knows how to connect
   print sockAddrs >> hFlush stdout
 
   (appThread, quitApp) <- runApp env sockets
   wait appThread `finally` quitApp
-

src/Language/Haskell/PtGhci/StartPy.hs

@@ -34,7 +34,6 @@ startPythonApp env (requestAddr, controlAddr, iopubAddr) = do
   setEnv "PTGHCI_REQUEST_ADDR" requestAddr
   setEnv "PTGHCI_CONTROL_ADDR" controlAddr
   setEnv "PTGHCI_IOPUB_ADDR" iopubAddr
-  printDebugInfo env
   s <- newCString $ unlines [ "import os, sys"
                              ,"from ptghci.app import App"
                              ,"app = App()"
@@ -48,6 +47,7 @@ startPythonApp env (requestAddr, controlAddr, iopubAddr) = do
   where
     runPy s done = do
       pyInitialize
+      printDebugInfo env
       res <- pyRunSimpleString s
       when (res == -1) $
         logerr env $ "Python exited with an exception"
@@ -72,7 +72,7 @@ startPythonApp env (requestAddr, controlAddr, iopubAddr) = do
 
 printDebugInfo :: Env -> IO ()
 printDebugInfo env = do
-  debug env $ "Python thread starting"
+  debug env $ "Python thread started"
   pyVer <- pyGetVersion >>= peekCString
   pyPath <- pyGetPath >>= peekCWString
   debug env $ "Python version " ++ pyVer