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SassMeister-input.scss

// ----
// Sass (v3.3.9)
// Compass (v1.0.0.alpha.20)
// ----

// Checks type of each item in list
// -------------------------------------------------------------------------------
// @param $list [list] : list of items
// @param $assert-types [string | list] : assert type for items
// @param $assert-length [number] : assert length of list
// -------------------------------------------------------------------------------
// @return [bool]

@function types-in-list($list, $assert-types: null, $assert-length: null) {
    @if type-of($list) == 'list' {

        // Assert types in list?
        // ----
        @if $assert-types {

            // Assert length of list?
            // ----
            @if $assert-length {
                // Get length of list
                $length: length($list);

                // Make sure lengths match
                @if $length == $assert-length {
                    // Keep empty list of types
                    $types: ();

                    // List of asserted types?
                    // ----
                    @if type-of($assert-types) == 'list' {
                      @if length($assert-types) == $length {

                        // Loop over each item in list
                        @for $i from 1 through $assert-length {
                            $item: nth($list, $i);
                            $type: nth($assert-types, $i);

                            // Check if type of item matches asserted type
                            @if type-of($item) != $type {
                                @return false;
                            }

                            $types: append($types, $type);
                        }
                      } @else {
                        @return false;
                      }

                    // Assert a single type
                    // ----
                    } @else {
                        // Assert single type
                        $type: nth($assert-types, 1);

                        // Loop over each item in list
                        @for $i from 1 through $assert-length {
                            $item: nth($list, $i);

                            // Check if type of item matches asserted type
                            @if type-of($item) != $type {
                                @return false;
                            }
                        }
                        
                        $types: append($types, $type);
                    }

                    // Return list of types
                    @return true; // $types;

                // Lengths did not match, return false
                } @else {
                    @return false;
                }

            // Just assert types in list
            // ----
            } @else {
                // Get asserted type
                $type: $assert-types;

                // Check each items type
                @each $item in $list {
                    // Check if type of item matches asserted type
                    @if type-of($item) != $type {
                        @return false;
                    }
                }

                // Passed check, return type
                @return true; // $type;
            }

        // Just grab type of first item in list
        // ----
        } @else {
            // Get type of first item in list
            $type: type-of(nth($list, 1));

            // Check each items type
            @each $item in $list {
                // Check if type of item matches asserted type
                @if type-of($item) != $type {
                    @return false;
                }
            }

            // Passed check, return type
            @return $type;
        }
    } @else {
        @return false;
    }
}

$nums: 1, 2, 3, 4, 5;
$strs: "one", "two", "three", "four", "five";
$assortment: 1, 2, "three", 4, 5;

tests {
  nums: types-in-list($nums, "number");
  nums-assert-length: types-in-list($nums, "number", 5);
  strs: types-in-list($strs, "string");
  strs-assert-length: types-in-list($strs, "string", 4);
  assortment: types-in-list($assortment, "number" "number" "string" "number" "number", 5);
  first-type-in-list: types-in-list($strs);
}

SassMeister-output.css

tests {
  nums: true;
  nums-assert-length: true;
  strs: true;
  strs-assert-length: false;
  assortment: true;
  first-type-in-list: string;
}