Functional Programming Functions

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;
}

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