Compass List Helpers

List Helpers is a Compass extension providing useful list helper functions like: map, filter, reduce, every and some.

The List Helpers are based on JavaScript's Array.prototype functions, but of course, adapted to Sass. Instead of passing in a function object in JS, in Sass you'd just pass in a function name, that will be called for each item in the list.

Install List Helpers by:

$ gem install compass-list-helpers

Tell Compass you want to use List Helpers in your project's config.rb:

require "list-helpers"

And import List Helpers into your stylesheet:

@import "list-helpers";

Not using Compass? Just copy and paste the contents of the stylesheets dir into your project.

As always, simple (silly) examples explain the rationale the best. It all starts with a list:

$my-awesome-colors: red, green, blue, yellow, blue, brown;
$my-awesome-numbers: 1, 2, 3, 4, 10, 20, 30;

Then, we would define some functions to test each item against:

// `is-blue` returns true if $item is blue, else it returns false.
@function is-blue($item) {
	@if $item == blue {
		@return true;
	}
	@return false;
}

// `add-numbers` adds two numbers, rocket science!
@function add-numbers($a, $b) {
	@return $a + $b;
}

// `double-up` doubles a number.
@function double-up($a) {
	@return $a * 2;
}

// `is-big-enough` returns true if $item is >= 10, else it returns false.
@function is-big-enough($item) {
	@if $item >= 10 {
		@return true;
	}
	@return false;
}

Now, if your using Sass 3.2 or lower, you need to define a call function. In Sass 3.3 a native call function is built-in, so there's no need for this poor man's solution:

// Note: only do this in Sass 3.2 or lower, in Sass 3.3 and higher there's no need for this.
@function call($function, $arguments...) {
	@if $function == 'is-blue' {
		@return is-blue($arguments...);
	}
	@if $function == 'add-numbers' {
		@return add-numbers($arguments...);
	}
	@if $function == 'double-up' {
		@return double-up($arguments...);
	}
	@if $function == 'is-big-enough' {
		@return is-big-enough($arguments...);
	}
}

Here comes the meat: now we can use the list helpers:

$the-blues: filter($my-awesome-colors, 'is-blue'); // Returns (blue, blue)
$big-is-better: filter($my-awesome-numbers, 'is-big-enough'); // Returns (10, 20, 30)
$all-blue: every($my-awesome-colors, 'is-blue'); // Returns false (not all items are blue)
$some-blue: some($my-awesome-colors, 'is-blue'); // Returns true (at least one item is blue)
$doubled: map($my-awesome-numbers, 'double-up'); // Returns (2, 4, 6, 8, 20, 40, 60)
$grand-total: reduce($my-awesome-numbers, 'add-numbers'); // Returns 70

List Helpers provides some useful functions:

Tests whether all items in the list pass the test implemented by the provided callback function.

Every executes the provided callback function once for each item present in the list until it finds one where callback returns false. If such an item is found, the every method immediately returns false. Otherwise, if callback returned a true value for all items, every will return true.

See the every test cases for more examples.

Creates a new list with all items that pass the test implemented by the provided function.

Filter calls a provided callback function once for each item in a list, and constructs a new list of all the values for which callback returns true.

See the filter test cases for more examples.

Creates a new list with the results of calling a provided function on every item in this list.

Map calls a provided callback function once for each item in a list, in order, and constructs a new list from the results.

See the map test cases for more examples.

Apply a function against an accumulator and each item of the list (from left-to-right) as to reduce it to a single value.

Reduce executes the callback function once for each item present in the list, passing it the result up until then and the current item in the list.

The $initial argument is the value to use as the first argument to the first call of the callback. For example, if you're adding up the $my-awesome-numbers list of numbers from above, you can $initial to 10 in order to start adding at 10 (so it will return 80).
In another example, if you're dealing with a list of lists you want to flatten, passing in an empty list as $initial will make sure the callback is properly called.

See the reduce test cases for more examples.

Tests whether some item in the list passes the test implemented by the provided callback function.

Some executes the callback function once for each item present in the list until it finds one where callback returns a true value. If such an item is found, some immediately returns true. Otherwise, some returns false.

See the some test cases for more examples.

MIT License, see LICENSE.txt.