Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.2)
// Compass (v1.0.0.alpha.17)
// ----

$a: 1 2 3 4;
$b: 2 3 4;

@function matrix($a, $b) {
  $c: ();
  @each $i in $a {
    $c: append( $c, if(
      type-of($b)=="list",
      matrix($b, $i),
      $i * $b
    ));
  }
  @return $c;
}

// matrix test print
@mixin print_matrix($m) {
  #matrix-test {
    @for $i from 1 through length($m) {
      l#{$i}: nth($m,$i);
    }
  }
}

$c: matrix($a, $b);
@include print_matrix($c);

SassMeister-output.css

#matrix-test {
  l1: 2 3 4;
  l2: 4 6 8;
  l3: 6 9 12;
  l4: 8 12 16;
}