pub fn get(
  output_map: MidiOutputMap,
  key key: String,
) -> Result(MidiOutput, Nil)

pub fn has(output_map: MidiOutputMap, key key: String) -> Bool

pub fn map(
  output_map: MidiOutputMap,
  with fun: fn(String, MidiOutput) -> a,
) -> a

pub fn size(output_map: MidiOutputMap, key key: String) -> Int