A first attempt at semantic/stateful grid mix-ins for Stylus.
Override the $grid-gutter-size and $grid-column-size variables with desired grid-system metrics, and $grid-max-columns with the desired maximum number of columns.
Use row() to start a new row within the grid-system, then use col(1) to generate a column, etc.
The number of columns within a row is counted, and errors will be thrown if you don't start a row() before calling col(), or if the total number of columns exceeds $grid-max-columns.
Example: