@function foo($this, $my) {
  @return (this: $this, my: $my);
}

a {
  $map: foo((this: is, my: map)...);
  @each $k, $v in $map {
    #{$k}: $v;
  }
}

b {
  $map: call("foo", (this: is, my: map)...);
  @each $k, $v in $map {
    #{$k}: $v;
  }
}