text: import {hcl} from "d3-color";
  import deltaHue from "./deltaHue";
  
  export default function(a, b) {
    a = hcl(a);
    b = hcl(b);
    var ah = isNaN(a.h) ? b.h : a.h,
        ac = isNaN(a.c) ? b.c : a.c,
        al = a.l,
        bh = isNaN(b.h) ? 0 : deltaHue(b.h, ah),
        bc = isNaN(b.c) ? 0 : b.c - ac,
        bl = b.l - al;
    return function(t) {
      a.h = ah + bh * t;
      a.c = ac + bc * t;
      a.l = al + bl * t;
      return a + "";
    };
  };
  