Echo extraneous output after prompt has been received

When the REPL spits out more stdout when no command is (ostensibly) in
progress, echo that output before the prompt.

Example case:

λ> forkIO (do threadDelay (1000*1000); putStrLn "yo")
ThreadId 37

yo
λ>

The "yo" is usually just lost in the ether. It also doesn't disturb
your prompt if you're typing in it.

@hvr @cmears might be interested.

haskell-interactive-mode.el

@@ -138,6 +138,11 @@ Key bindings:
   "Face for the result."
   :group 'haskell-interactive)
 
+(defface haskell-interactive-face-garbage
+  '((t :inherit 'font-lock-string-face))
+  "Face for trailing garbage after a command has completed."
+  :group 'haskell-interactive)
+
 (defun haskell-interactive-mode-newline-indent ()
   "Make newline and indent."
   (interactive)
@@ -461,6 +466,16 @@ SESSION, otherwise operate on the current buffer.
                               'read-only t
                               'rear-nonsticky t)))))))
 
+(defun haskell-interactive-mode-insert-garbage (session message)
+  "Echo a read only piece of text before the prompt."
+  (with-current-buffer (haskell-session-interactive-buffer session)
+    (save-excursion
+      (haskell-interactive-mode-goto-end-point)
+      (insert (propertize message
+                          'face 'haskell-interactive-face-garbage
+                          'read-only t
+                          'rear-nonsticky t)))))
+
 (defun haskell-interactive-mode-insert (session message)
   "Echo a read only piece of text before the prompt."
   (with-current-buffer (haskell-session-interactive-buffer session)

haskell-process.el

@@ -1065,10 +1065,12 @@ If I break, you can:
   (haskell-process-log (format "<- %S\n" response))
   (let ((session (haskell-process-project-by-proc proc)))
     (when session
-      (when (haskell-process-cmd (haskell-session-process session))
-        (haskell-process-collect session
+      (if (haskell-process-cmd (haskell-session-process session))
+          (haskell-process-collect session
                                  response
-                                 (haskell-session-process session))))))
+                                 (haskell-session-process session))
+        (haskell-interactive-mode-insert-garbage session
+                                                 response)))))
 
 (defun haskell-process-log (msg)
   "Write MSG to the process log (if enabled)."