Use barchecks to auto-split music into grid cells

[uliska]

This issue is just for my own note-keeping.

When thinking about an interface to MEI I came across the idea of using GridLY to create a compatible input structure to map LilyPond's input to MEI's (mostly) measure-based encoding structure. Having a grid with each cell representing one measure of a part comes very close to MEI's concept.

For this to be at least viable we need a non-intrusive interface to enter music measure-based. There is the \parallelMusic approach but I'm not sure that is a good idea in this context.

I thought about a command that takes a list of music expressions and stores them in subsequent cells of the grid. Then I thought about using barchecks for that cause. This could even be realized by modifying the existing \gridPutMusic with an extra flag-style option. Then barchecks in the music option would be parsed and used to split the music expression in consecutive items to be stored in the grid's cells.

[uliska]

I now see that this would be a nice addition even without the concrete "measure" restriction. I suggest a command to enter music in a sequence of cells, one horizontally and one vertically. The horizontal one could (maybe) even take care of necessary opening/closing contents.

The idea is to provide a single ly:music? argument and split that into chunks using barchecks.

\displayMusic { 
  | 
}

=> 

#(make-music
  'SequentialMusic
  'elements
  (list (make-music (quote BarCheck))))

shows that this should be possible. These chunks are then stored to consecutive cells, starting from a given cell. A direction parameter could decide about the direction (hor/vert).

In that situation it doesn't matter whether the cells hold single measures or not, it would nevertheless be a way to conveniently (and LilyPond-ishly) enter consecutive cell contents. And no, this doesn't compromise the library's idea.

[uliska]

When entering consecutive cells in a vertical fashion the command could have an optional property that specifies a list of "row" contexts. Otherwise the user would have to supply empty elements for the contexts that currently don't play. This is a) tedious, b) error-prone and c) pretty impractical when copying from a frenched score. It should probably be easier to write

\gridPutMusicCells \with {
  start = 28 % measure number or column index
  direction = #'VERT
  rows = #'("fluteI" "fluteII" "clarinetII")
  music = { c''1 | a''2 g'' | e''1 }
}

than having to use

music = { c''1 | a''2 g'' | R1 | R1 | R1 | e''1 }

and "count" the empty contexts for the oboes and clarinet 1.