$sizeUnit: rem;
$marginKey: 'm';
$paddingKey: 'p';
$separator: '-';
$sizes: (('sm', 0.5), ('md', 1), ('lg', 2), ('xl', 4), ('xxl', 8));
$positions: (('t', 'top'), ('r', 'right'), ('b', 'bottom'), ('l', 'left'));

@function sizeValue($key, $value) {
    @return if($key == 'none', 0, $value + $sizeUnit);
}

@each $size in $sizes {
    $sizeKey: nth($size, 1);
    $sizeValue: nth($size, 2);
    .#{$marginKey}#{$separator}#{$sizeKey} {
        margin: sizeValue($sizeKey, $sizeValue);
    }
    .#{$paddingKey}#{$separator}#{$sizeKey} {
        padding: sizeValue($sizeKey, $sizeValue);
    }
    @each $position in $positions {
        $posKey: nth($position, 1);
        $posValue: nth($position, 2);
        .#{$marginKey}#{$separator}#{$posKey}#{$separator}#{$sizeKey} {
            margin-#{$posValue}: sizeValue($sizeKey, $sizeValue);
        }
        .#{$paddingKey}#{$separator}#{$posKey}#{$separator}#{$sizeKey} {
            padding-#{$posValue}: sizeValue($sizeKey, $sizeValue);
        }
    }
}