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# Functional Programming Functions

Published

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For library makers and framework builders, having a couple of extra functions to dynamically apply functions to items of a list might come in handy. Here are 4 functions inspired by JavaScript and PHP equivalents, implemented in Sass.

### walk()

The `walk()`

function applies a given function to every item of a list.

```
/// Apply `$function` with `$args` to each item from `$list`.
/// @author Hugo Giraudel
/// @param {List} $list - List of items
/// @param {String} $function - Function to apply to every item from `$list`
/// @param {Arglist} $args - Extra arguments to pass to `$function`
/// @return {List}
/// @throw There is no `#{$function}` function.
@function walk($list, $function, $args...) {
@if not function-exists($function) {
@error "There is no `#{$function}` function.";
}
@for $i from 1 through length($list) {
$list: set-nth($list, $i, call($function, nth($list, $i), $args...));
}
@return $list;
}
```

#### Usage

```
walk {
walk: walk(red green blue, invert);
walk: walk(red green blue, lighten, 20%);
walk: walk(2 4 6 8 10, sqrt);
}
```

```
walk {
walk: cyan #ff7fff yellow;
walk: #ff6666 #00e600 #6666ff;
walk: 1.41421 2 2.44949 2.82843 3.16228;
}
```

### some()

The `some()`

function returns whether some items from a list pass test given (as a function).

```
/// Return whether some items from `$list` passed `$function` test.
/// @author Hugo Giraudel
/// @param {List} $list - List of items
/// @param {String} $function - Function to run on every item from `$list`
/// @param {Arglist} $args - Extra arguments to pass to `$function`
/// @return {Boolean}
/// @throw There is no `#{$function}` function.
@function some($list, $function, $args...) {
@if not function-exists($function) {
@error "There is no `#{$function}` function.";
}
@each $item in $list {
@if call($function, $item, $args...) {
@return true;
}
}
@return false;
}
```

#### Usage

```
some {
some: some(round ceil floor, function-exists);
some: some(round ceil unknown, function-exists);
some: some(completely unknown function, function-exists);
some: some(4px 10px 20px, comparable, 42px);
some: some(4px 10% 20px, comparable, 42%);
some: some(4px 10px 20px, comparable, 42%);
}
```

```
some {
some: true;
some: true;
some: false;
some: true;
some: true;
some: false;
}
```

### every()

The `every()`

function returns whether every items from a list pass test given (as a function).

```
/// Return whether all items from `$list` passed `$function` test.
/// @author Hugo Giraudel
/// @param {List} $list - List of items
/// @param {String} $function - Function to run on every item from `$list`
/// @param {Arglist} $args - Extra arguments to pass to `$function`
/// @return {Boolean}
/// @throw There is no `#{$function}` function.
@function every($list, $function, $args...) {
@if not function-exists($function) {
@error "There is no `#{$function}` function.";
}
@each $item in $list {
@if not call($function, $item, $args...) {
@return false;
}
}
@return true;
}
```

#### Usage

```
every {
every: every(round ceil floor, function-exists);
every: every(round ceil unknown, function-exists);
every: every(completely unknown function, function-exists);
every: every(4px 10px 20px, comparable, 42px);
every: every(4px 10% 20px, comparable, 42%);
every: every(4px 10px 20px, comparable, 42%);
}
```

```
every {
every: true;
every: false;
every: false;
every: true;
every: false;
every: false;
}
```

### functions-walk()

The `functions-walk()`

function returns a list made of the result of each function call.

```
/// Return a list made of the result of each function call from `$functions` with `$args`.
/// @author Hugo Giraudel
/// @param {List} $functions - List of functions to call
/// @param {Arglist} $args - Extra arguments to pass to each function in `$functions`
/// @return {List}
/// @throw There is no `#{$function}` function.
@function functions-walk($functions, $args...) {
$list: ();
@each $function in $functions {
@if not function-exists($function) {
@error "There is no `#{$function}` function.";
}
$list: append($list, call($function, $args...));
}
@return $list;
}
```

#### Usage

```
functions-walk {
functions-walk: functions-walk('red' 'blue' 'green', #BADA55);
functions-walk: functions-walk('round' 'ceil' 'floor', 3.1415279);
}
```

```
functions-walk {
functions-walk: 186 85 218;
functions-walk: 3 4 3;
}
```