/// Checks whether all entries from `$matrix` are numeric
/// @group checkers
/// @param {Matrix} $matrix - matrix
/// @return {Bool}
/// @require {function} rows
/// @require {function} columns
/// @require {function} get-entry
@function is-numeric($matrix) {
  @for $i from 1 through rows($matrix) {
    @for $j from 1 through columns($matrix) {
      @if type-of(get-entry($matrix, ($i $j))) != "number" {
        @return false;
      }
    }
  }
  @return true;
}