Lensing? or hard-coded operators?

[sleexyz]

The issue right now is that operators like add are hard coded to add to the midi note.

add 0 7 12 13

We might want some concise way of adding to values like velocity, or duration.

otherwise we'll have a bunch of operators like

vel_add 60

or

dur_add 1

which honestly might be fine, since this is a domain specific language.

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If we really want lensing, then we should support maybe something like

vel add 0  7 12 13

or

add vel 0 7 12 13

or a higher-order operator, like

(vel add) 0 7 12 13