// usage:

@letter-spacing:
    base 0,
    foo  5rem,
    xs   0.2px;

.make-something(letter-spacing);

// impl.:

.make-something(@id) {
    .@{id} {
        .for(@@id); .-each(@v) {
            @key: extract(@v, 1);
            &--@{key} {@{id}: extract(@v, 2)}
        }
    }
}

@import "for";