Generated by SassMeister.com, the Sass playground.

SassMeister-input.sass

// advanced list operation experiments; part of a larger codebase

@function contains($list, $var)
  @return index($list, $var) != false

@function nested-contains($list, $key)
  @each $tuple in $list
    @if index($tuple, $key) != false
      @return true
  @return false

@function nested-index($list, $key)
  @each $tuple in $list
    @if index($tuple, $key) != false
      @return index($list, $tuple) index($tuple, $key)
  @return false

@function remainder($list, $item)
  $out: ()
  @each $arg in $list
    @if $arg != $item
      $out: append($out, $arg)
  @return $out

@function tuple-values($list, $key)
  @each $tuple in $list
    @if index($tuple, $key)
      @return reject($tuple, $key)
  @return false

@function tuple-values-2($list, $key, $key2)
  @each $tuple in $list
    @if index($tuple, $key)
      $list2: reject($tuple, $key)
      @each $tuple2 in nth($list2,1)
        @if index($tuple2, $key2)
          @return reject($tuple2, $key2)
  @return false

$complex-list: 32px, trim bottom top, height 0.75, collapse top

.tuple-values-test
  trim-contains: nested-contains($complex-list, trim)
  trim-index: nested-index($complex-list, collapse)
  trim-values: tuple-values($complex-list, trim)
  height-values: tuple-values($complex-list, height)
  collapse-value: tuple-values($complex-list, collapse)

$fonts: body (family unquote('"Helvetica", Helvetica'), topline 0.8, capline 0.75, midline 0, baseline 0.75, beardline 0.9), heading (family "Georgia", topline 0.8, capline 0.75, midline 0, baseline 0.75, beardline 0.9)
$body-data: tuple-values($fonts, body)

.font-data-test
  font-family: tuple-values-2($fonts, body, family)
  capline: tuple-values-2($fonts, body, capline)    

SassMeister-output.css

.tuple-values-test {
  trim-contains: true;
  trim-index: 4 1;
  trim-values: bottom top;
  height-values: 0.75;
  collapse-value: top;
}

.font-data-test {
  font-family: "Helvetica", Helvetica;
  capline: 0.75;
}