$ease: (
  'linear'             : cubic-bezier(0.250, 0.250, 0.750, 0.750),
  'ease'               : cubic-bezier(0.250, 0.100, 0.250, 1.000),
  'ease-in'            : cubic-bezier(0.420, 0.000, 1.000, 1.000),
  'ease-in-out'        : cubic-bezier(0.420, 0.000, 0.580, 1.000),
  'ease-in-quad'       : cubic-bezier(0.550,  0.085, 0.680, 0.530),
  'ease-in-cubic'      : cubic-bezier(0.550,  0.055, 0.675, 0.190),
  'ease-in-quart'      : cubic-bezier(0.895,  0.030, 0.685, 0.220),
  'ease-in-quint'      : cubic-bezier(0.755,  0.050, 0.855, 0.060),
  'ease-in-sine'       : cubic-bezier(0.470,  0.000, 0.745, 0.715),
  'ease-in-expo'       : cubic-bezier(0.950,  0.050, 0.795, 0.035),
  'ease-in-circ'       : cubic-bezier(0.600,  0.040, 0.980, 0.335),
  'ease-in-back'       : cubic-bezier(0.600, -0.280, 0.735, 0.045),
  'ease-out'           : cubic-bezier(0.000, 0.000, 0.580, 1.000),
  'ease-out-quad'      : cubic-bezier(0.250,  0.460, 0.450, 0.940),
  'ease-out-cubic'     : cubic-bezier(0.215,  0.610, 0.355, 1.000),
  'ease-out-quart'     : cubic-bezier(0.165,  0.840, 0.440, 1.000),
  'ease-out-quint'     : cubic-bezier(0.230,  1.000, 0.320, 1.000),
  'ease-out-sine'      : cubic-bezier(0.390,  0.575, 0.565, 1.000),
  'ease-out-expo'      : cubic-bezier(0.190,  1.000, 0.220, 1.000),
  'ease-out-circ'      : cubic-bezier(0.075,  0.820, 0.165, 1.000),
  'ease-out-back'      : cubic-bezier(0.175,  0.885, 0.320, 1.275),
  'ease-in-out-quad'   : cubic-bezier(0.455,  0.030, 0.515, 0.955),
  'ease-in-out-cubic'  : cubic-bezier(0.645,  0.045, 0.355, 1.000),
  'ease-in-out-quart'  : cubic-bezier(0.770,  0.000, 0.175, 1.000),
  'ease-in-out-quint'  : cubic-bezier(0.860,  0.000, 0.070, 1.000),
  'ease-in-out-sine'   : cubic-bezier(0.445,  0.050, 0.550, 0.950),
  'ease-in-out-expo'   : cubic-bezier(1.000,  0.000, 0.000, 1.000),
  'ease-in-out-circ'   : cubic-bezier(0.785,  0.135, 0.150, 0.860),
  'ease-in-out-back'   : cubic-bezier(0.680, -0.550, 0.265, 1.550)
);

@function ease($key: ease) {
  @if map-has-key($ease, $key) {
    @return map-get($ease, $key);
  }

  @warn "Unkown '#{$key}' in $ease.";
  @return null;
}