-?>>

    macro
    boot.janet on line 1427, column 1

    ($-?>>$ x & forms)

    Short circuit threading macro. Inserts x as the last value in the 
    first form in `forms`, and inserts the modified first form into the 
    second form in the same manner, and so on. The pipeline will return 
    nil if an intermediate value is nil. Useful for expressing 
    pipelines of data.