Complex Sass breakpoint declaration

breaks.scss

@function column-width($cols) {
	@return 90px * $cols;
}
@function column-under-width($cols) {
	@return (90px * $cols) - 1;
}
@function over-mq($w) {
	@return "screen and (min-width: #{$w})";
}
@function under-mq($w) {
	@return "screen and (max-width: #{$w})";
}

// 15 cols: 1350px
$break-15: column-width(15);
$break-15-mq: over-mq($break-15);
$break-under-15: column-under-width(15);
$break-under-15-mq: under-mq($break-under-15);

// 13 cols: 1170px
$break-13: column-width(13);
$break-13-mq: over-mq($break-13);
$break-under-13: column-under-width(13);
$break-under-13-mq: under-mq($break-under-13);

// 11 cols: 990px
$break-11: column-width(11);
$break-11-mq: over-mq($break-11);
$break-under-11: column-under-width(11);
$break-under-11-mq: under-mq($break-under-11);

// 9 cols: 810px
$break-9: column-width(9);
$break-9-mq: over-mq($break-9);
$break-under-9: column-under-width(9);
$break-under-9-mq: under-mq($break-under-9);