static Complex complex(double re, double im) {
  ret Complex(re, im);
}

static Complex complex(double re) {
  ret Complex(re, 0.0);
}

static Complex complex(double[] reIm) {
  if (empty(reIm)) null;
  if (l(reIm) != 2) fail("Need 2 doubles to make complex number");
  ret complex(reIm[0], reIm[1]);
}

Began life as a copy of #1032421