MidiManager is a VST plugin that allows you to write scripts using [Pure programming language] (http://purelang.bitbucket.org/). The plugin is written using [Juce Framework] (http://www.juce.com/). MidiManager is currenlty only available for Mac OS X. The plugin requires Pure installed on your system, which can be simply installed using brew:

brew intall pure

The project is still in a very early stage and currently has a very basic interface that allows you to load a pure script, and the plugin will then load and compile the script and execute it.

The plugin currently supports only MIDI input and output and will look for a function called processMidiBuffer that accepts a list of tuples, where each tuple on the form (event, position) representing the MIDI event and the position of this event in the buffer. There is a Pure script that contains some helper functions to assist extracting information about the current MIDI event as well as constructing new events, and it will be available to the plugin using the Pure using midi; statement. The full script can be found here

Here's a pure script that will simply echo every event it gets:

processMidiBuffer buf = buf;

The following example turns any note into a major chord:

using midi;

let major = [0,4,7];

processMidiBuffer buf =
  result with
    process m = 
      case to_note_t m of
        (NoteOn c n v) = map (\i -> (note_on_message c (n+i) v (position m))) major;
        (NoteOff c n)  = map (\i -> (note_off_message c (n+i) (position m))) major;
        _              = [m];
      end;
    result = to_tuple_list $ catmap process $ to_message_t buf;
  end;

In this example, the result rule turns the input into a list of type message_t which holds the MIDI event along with its position in the buffer. Then output is sent to the process rule to create messages and finally the output is turned again into a tuple format using the to_tuple_list function. The rules: to_message_t, to_tuple_list, to_note_t are all made available through the imported using midi file.