Slightly disappointed in Nemerle

I've been coding with Nemerle a bit during the last couple of months. I've discovered that I had set my expectations too high. It doesn't quite live up to them. Might be as much my fault as Nemerle's, but that doesn't really change anything.

I was hoping for a experience closer to OCaml (only with better cross platform library support) than I got. With OCaml, once your code compiles, you know you are doing pretty good. With Nemerle, not so much. First of all, it feels like you get to fight a bit more with the type inferer than in OCaml. This is probably partially due to the maturity of the implementation, partially due to the fact that with OCaml, I didn't use as serious class hierarchies as I do with Nemerle, thanks to the .NET standard library and heavier Gtk+ usage.

The second problem I've encountered is that when you interface a lot with C# code, you don't really get much mileage out of the functional stuff in Nemerle. When you have a List generated in C#, you don't get to fold over it. While Nemerle does have the ICollection interface extending System.Collections.Generic.ICollection with all the functional iteration tools, there are no wrapper classes and no standalone functions. If you want a foldable List, you'll have to copy stuff. Not nice.

And third, while the variables are by default non-mutable, which is nice, and when you define your types in Nemerle you can do matching and get the safety that brings, you end up interacting so much with .NET code that you have to do the normal null checks all over the place anyway.

In short, the benefits of Nemerle over the current features of C# are feel pretty limited. Maybe it would be better if you were working with pure Nemerle projects, but at least interacting with C# eliminates most of them.

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Making Emacs understand ncc errors

Add this to your .emacs or equivalent to make Emacs' compilation-mode make proper links out of the Nemerle compiler's error messages:

(setq compilation-error-regexp-alist 
    (append compilation-error-regexp-alist 
            '(("^\\(.+\\):\\([0-9]+\\):\\([0-9]*\\):\\(?:[0-9]*\\):\\(?:[0-9]*\\):" 
            1 2 3))))

Update:

Or even better, using rx (thanks to this hint for reminding me about it):

(setq compilation-error-regexp-alist 
      (append compilation-error-regexp-alist 
              `((,(rx line-start 
                      (group (1+ (not (any ":"))))
                      ":" 
                      (group (1+ digit)) 
                      ":" 
                      (group (1+ digit)) 
                      ":" 
                      (*? digit) 
                      ":" 
                      (*? digit) 
                      ": ") 1 2 3))))
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C# export for Gaphor

Gaphor is the best free UML tool for X I've seen yet. It's far from finished but at least it produces pretty graphs. I started writing a C# export plugin for it. The first somewhat working version is available. This has been developed with 0.10.4, no guarantees of it working with any other version. No guarantees of it working with that version either, to be exact, but at least it works for me.

Extract it inside Gaphor's source directory, in gaphor/data/plugins.

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Python, Queue, Pygame and the GLib mainloop

The GLib mainloop is what you're probably running in your Python program when you are using PyGTK or GStreamer.

Sometimes you want to integrate other event sources to it. The documentation for this is a bit thin; all I've seen is GLib's page on the main event loop, GSourceFuncs section and test-source.py in pygobject. Here I'm presenting two snippets displaying how to do it with two systems I've needed to work with. No guarantees on their correctness, but they do seem to work. Both are parts of larger modules, so they aren't usable by themselves and aren't really tidied up to look like proper examples. However, they should give you the general idea.

Here's how to do it with Python's Queue:

class QueueSource(gobject.Source):
    def __init__(self, queue):
        gobject.Source.__init__(self)
        self._queue = queue
        self.logger = loghelper.get_logger(self)

    def prepare(self):
        return False

    def check(self):
        return not self._queue.empty()

    def dispatch(self, callback, args):
        self.logger.debug("dispatch called, callback: " + str(callback))
        if callback is not None:
            self.logger.debug("dispatch calling callback: " + str(callback))
            v = callback(self._queue.get(), *args)
            self.logger.debug("dispatch returned " + str(v))
        return True

    def finalize(self):
        self.logger.debug("finalize called")


m = QueueSource(self._queue)
def my_callback(command, *args):
    self.logger.debug("my_callback: args: " + str(command) + ", " + str(args))
    self.logger.debug("my_callback: thread: " + str(threading.currentThread()))
    if command == self.PLAY:
        self._player.play()
    elif command == self.STOP:
        self._player.stop()
    elif command == self.SKIP:
        self._player.skip()

m.set_callback(my_callback, mainloop)
m.attach()

And here's Pygame:

class PygameEventSource(gobject.Source):
    def __init__(self):
        gobject.Source.__init__(self)
        self.logger = loghelper.get_logger(self)

    def prepare(self):
        return False

    def check(self):
        try:
            pygame.event.pump()
            p = pygame.event.peek(
                [KEYUP, KEYDOWN, VIDEOEXPOSE, VIDEORESIZE, NUMEVENTS, QUIT,
                 ACTIVEEVENT, USEREVENT])
            return p
        except Exception, ex:
            self.logger.error("Caught an exception while checking for events",
                              exc_info=True)

    def dispatch(self, callback, args):
        if callback is not None:
            try:
                e = pygame.event.poll()
                v = callback(e, *args)
                return v
            except (KeyboardInterrupt, SystemExit):
                self.logger.warn(
                    "Caught a terminating exception while dispatching to the "
                    "callback, re-raising", exc_info=True)
                pygame.display.quit()
                raise
            except Exception, ex:
                self.logger.error(
                    "Caught an exception while dispatching to the callback",
                    exc_info=True)
        return True

    def finalize(self):
        pass

def my_callback(self, event, *args):
    if event.type == QUIT:
        sys.exit()
    if event.type == KEYDOWN:
        self.logger.debug("my_callback: keydown: event.key: " + str(event.key))
        if event.key in (K_q,):
            sys.exit()
        elif event.key in (K_n, K_SPACE):
            self._player.skip()
        elif event.key in (K_p,):
            if self._player.playing:
                self._player.stop()
            else:
                self._player.play()

    return True


def start_mainloop(self, mainloop):
    self.logger.debug("Starting mainloop")
    if not self._started:
        s = PygameEventSource()
        s.set_callback(self.my_callback, mainloop)
        s.attach()
    return
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One of Those Things You Don't Know If You Should Post in Your Blog Or on TheDailyWTF

From Rails, or more specifically, ActiveSupport's json.rb:

# When +true+, Hash#to_json will omit quoting string or symbol keys
# if the keys are valid JavaScript identifiers.  Note that this is
# technically improper JSON (all object keys must be quoted), so if
# you need strict JSON compliance, set this option to +false+.
mattr_accessor :unquote_hash_key_identifiers
@@unquote_hash_key_identifiers = true
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AudioFormat 0.4 released

After a longish break, released a new AudioFormat when I noticed how aggravating the current version was :-)

The new version, 0.4, allows you to add files to the list of files to convert via a file selector or by dragging. It also should handle and report errors a bit better. And maybe it'll even recognize Vorbis files? Although I suspect it'll get very confused if it encounters something like Ogg Tarkin files. Will have to work on that a bit more.

Enjoy.

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