@for $i from 0 to 6 {
    .m-#{$i} {
        margin: $space * $i !important;
    }
}

@each $direction,
$short in $directions {
    @for $i from 0 to 6 {
        .m#{$short}-#{$i} {
            margin-#{$direction}: $space * $i !important;
        }
    }
}