fcn lanczosGamma(z) { z = z.toFloat();
    // Coefficients used by the GNU Scientific Library.
    // http://en.wikipedia.org/wiki/Lanczos_approximation
    const g = 7, PI = (0.0).pi;
    exp := (0.0).e.pow;
    var table = T(
             0.99999_99999_99809_93,
           676.52036_81218_851,
         -1259.13921_67224_028,
           771.32342_87776_5313,
          -176.61502_91621_4059,
            12.50734_32786_86905,
            -0.13857_10952_65720_12,
             9.98436_95780_19571_6e-6,
             1.50563_27351_49311_6e-7);

    // Reflection formula.
    if (z < 0.5) {
        return(PI / ((PI * z).sin() * lanczosGamma(1.0 - z)));
    } else {
        z -= 1;
        x := table[0];
        foreach i in ([1 .. g + 1]){
            x += table[i] / (z + i); }
        t := z + g + 0.5;
        return((2.0 * PI).sqrt() * t.pow(z + 0.5) * exp(-t) * x);
    }
}