Write a function that returns a spacing token by name.

Short Interview Answer

Accept key, look up in $spacers map, @error if missing, return value.

Detailed Explanation

Centralizes failures at compile time — better than emitting invalid CSS.

Example

@function space($k) {
  @if not map.has-key($spacers, $k) { @error 'Unknown #{$k}'; }
  @return map.get($spacers, $k);
}