// 16 arguments can be passed into this function
// a max of 16 comma seperated grids
@function compound($compound-grids...) {
  @if length($compound-grids) == 1 {
    $compound-grids: nth($compound-grids, 1);
  }

  // merge arguments into a single list.

  // Find the base resolution of grid
  $resolution: 1;
  @each $item in $compound-grids {
    $resolution: $resolution * $item;
  }

  $compound-grid: ();
  $compound-counter: 1;
  // cycle through each step in grid resolution
  @for $i from 1 through $resolution {

    // dont add a column by default
    $add-col: false;

    // cycle through all grids to see if any grids match
    @each $grid in $compound-grids {

      // if the grid divides evenly into the resolution, add a column
      // divide the resolution by number of columns to get the column resolution
      @if $i / ($resolution / $grid) == round($i / ($resolution / $grid)) {
        $add-col: true;
      }
    }

    // add the counter value to the compound grid list, reset counter
    // this marks where one column ends and a new one begins
    @if $add-col {
      $compound-grid: join($compound-grid, $compound-counter);
      $compound-counter: 1;
    }
    // if no column is added, bump up counter
    @else {
      $compound-counter: $compound-counter + 1;
    }
  }

  @return $compound-grid;
}