Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.2.19)
// Compass (v0.12.7)
// ----

$byline: (
   font-size          10px,
   font-size--large   15px,
   font-size--small   8px,
   width              200px,
   width--large       250px
);

@function get($list, $key, $keyword: null) {
  $keys: ();
  @each $pair in $list {
    $keys: append($keys, nth($pair, 1));
  }
  @if $keyword {
    $key: $key + '--' + $keyword;
  }
  $value: nth(nth($list, index($keys, $key)), 2);
  @return $value;
}

body {
  width: get($byline, width, large);
}

SassMeister-output.css

body {
  width: 250px;
}