$GLOBAL: global;

@function foo($g1, $g2, $g3) {
  @each $value in $g1, $g2, $g3 {
    $GLOBAL: $GLOBAL each $value;
    $GLOBAL: $GLOBAL type1 type-of(nth($value, 1));
    $GLOBAL: $GLOBAL type2 type-of(nth($value, 2));
  }
  @return 0;
}

div {
  a: foo(50% 50%, cover circle, red blue);
  b: $GLOBAL;
  $colors: red green blue;
  c: a, b, type-of(nth($colors, 2)), d;
}