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Higher-order functions for Sass 3.3 -- now that we've got the `call()` function in Sass, we can start to compose functions. We don't have the benefit of anonymous functions, of course, but this is real functional programming, folks!
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// 'map', 'transform', 'select', or 'project' function. Iterate over a list, | |
// performing a function on each item, and collecting the new items. Each | |
// function takes an item as a first argument and returns a transformed item. | |
// You can pass additional arguments to the function too, which is a decent poor | |
// man's function composition. | |
// (I didn't call this f-map because the term 'map' is already used in Sass to | |
// denote a hash or dictionary.) | |
@function f-apply($func, $list, $args...) { | |
$new-list: (); | |
@each $item in $list { | |
$new-list: append($new-list, call($func, $item, $args...)); | |
} | |
@return $new-list; | |
} | |
// Reduce a list to a single value. Each function takes the previous value, an | |
// item, and additional arguments, and returns a transformed value. Sadly, you | |
// can't leave out the initial value (can't have default arguments before rest | |
// arguments), so if you don't want an initial value, set it to null. | |
@function f-fold($func, $list, $initial, $args...) { | |
$start: 1; | |
@if $initial == null { | |
// If there's no initial value, use the first in the list. | |
$start: 2; | |
$initial: nth($list, 1); | |
} | |
$prev: $initial; | |
@for $i from $start through length($list) { | |
$next: nth($list, $i); | |
$prev: call($func, $prev, $next, $args...); | |
} | |
@return $prev; | |
} | |
// Filter items from a list. Each function takes an item (and additional | |
// arguments) and returns a boolean value indicating whether the item passed the | |
// filter. | |
@function f-filter($func, $list, $args...) { | |
$new-list: (); | |
@each $item in $list { | |
@if call($func, $item, $args...) { | |
$new-list: append($new-list, $item); | |
} | |
} | |
@return $new-list; | |
} |
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