Can't compile progressions about mezzo HOT 1 CLOSED

Hi! Thanks for your interest :)
I think the issue in your case is the play function: it is only intended to convert melodies into Music values, which is what prog does with progressions. In very simplistic terms, you have:

• Progression: the abstract type for chord progressions.
• Music: the main data type which performs the rule-checking.
• Score: type of MIDI tracks which can be exported into MIDI files.
• prog :: Progression -> Music: function to convert abstract progressions into concrete Music values.
• defScore :: Music -> Score: function to convert Music values into exportable MIDI tracks.

Hence you only need

p = defScore $ prog $ ph_IVI ton dom_V ton :+ cadence (full subdom_IV auth_V7_I)

As an aside, play was renamed to start in the latest release (which I just added) to avoid confusion with the live playback functions.

Once you have a Score (by applying defScore or the more general score construction functions to a Music value), you can use renderScore to render it into a MIDI file (that part of your program seems correct).

Thanks for the kind words! I do agree that type-level hackery is a bit risky – it's quite easy to break stuff and output an enormous and scary error message. However, it's quite nice when it works! I am considering rewriting Mezzo on the term level (or even TH, as you suggest) in the future to compare the benefits and drawbacks of the two approaches (though this will have to wait as I need to concentrate on a different project this year).

I hope this helped!

from mezzo.