PHP Functional Programming library. Monads and common use functions.


Functional PHP

PHP Functional Programming library. Monads and common use functions.

psalm level psalm type coverage phpunit coverage




$ composer require whsv26/functional

Enable psalm plugin (optional)

To improve type inference for particular functions

$ vendor/bin/psalm-plugin enable Fp\\Psalm\\FunctionalPlugin


Build documentation

  1. Install dependencies
[email protected]:~$ sudo apt install pandoc
  1. Generate doc from src
  • Improve type inference for Option and Either assertion

    Improve type inference for Option and Either assertion

    This PR aim to fix wrong type inference for Option and Either assertion methods. Example of correct inference:

     * @return Option<int>
    function getOption(): Option
        return Option::none();
    /** @psalm-param (Some<int>) $_some */
    function assertIsSome($_some): void {}
    /** @psalm-param (None) $_none */
    function assertIsNone($_none): void {}
    function test(): void
        $opt = getOption();
        if ($opt->isSome()) {
            assertIsSome($opt); // $opt is Some<int> at this point
        } else {
            assertIsNone($opt); // $opt is None, before it was Option<int>
    opened by klimick 4
  • Q: why does Option::get() may return null?

    Q: why does Option::get() may return null?

    Just noticed that Option::get() may return null value. Are there any specific reasons for this behavior?

    I mean, there are other implementations of Option and non of them do return null value.


    public T get() {
        if (value == null) {
            throw new NoSuchElementException("No value present");
        return value;


    def get: Nothing = throw new NoSuchElementException("None.get")


    pub fn unwrap(self) -> T {
        match self {
            Some(val) => val,
            None => panic!("called `Option::unwrap()` on a `None` value"),

    Maybe there is a contract for Option to have that kind of behavior?

    opened by nzour 3
  • Add method match on Option and Either?

    Add method match on Option and Either?

    Greetings, sir. Just got a few thoughts about implementing method match on Option and Either.

    Like C# functional lib has

    This would look like


    $hello = Option::of('Hello');
    $result = $hello->match(
        some: fn(string $v) => "{$v} world",
        none: fn() => 'Hello from none'


    /** @var Either<string, FooInterface> $found */
    $found = Some::of(new FooImpl());
        right: \Fp\id,
        left: function(string $errorMessage) {
            // sorry for side effect here
            return new BarImpl();

    So the method signature would look like:


     * @template TR
     * @param callable(A): TR $some
     * @param callable(): TR $none
     * @return TR
    public function match(callable $some, callable $none): mixed


     * @template TR
     * @param callable(R): TR $right
     * @param callable(L): TR $left
     * @return TR
    public function match(callable $right, callable $left): mixed

    I think this may be useful. What do you think?

    opened by nzour 3
  • Do we need function 'but_last' ?

    Do we need function 'but_last' ?

    Been thinking about function but_last, like this

    I am not sure if this function is necessary. Also we just may code something like this:

    $withoutLast = \Fp\Collection\reverse(
    // or simplified version
    $withoutLast = reverse(tail(reverse($collection)));

    Maybe native function but_last would be more understandable and less resource consuming? I would be pleasured to hear your opinion.

    opened by nzour 3
  • Any cases to add @psalm-pure for really pure functions?

    Any cases to add @psalm-pure for really pure functions?

    In some cases it may be useful to use few functions inside pure context.


     * @psalm-immutable
    class Foo
         * @var list<Bar>
        public array $bars;
        public function __construct(Bar $first, Bar ...$rest)
            // Impure method call issue occurred here (because Foo is immutable, so requires pure context)
            $this->bars = asList([$first], $rest);

    Of course, there are more ways to compile list, but if we have asList why wouldn't we use it whenever we want?

    I was just thinking about function asList, maybe there are few others function that are actually pure but not annotated yet

    opened by nzour 2
  • Option::do implementation incorrect

    Option::do implementation incorrect

    This snippet type checks by psalm, but at runtime it fails:

     * @return Option<stdClass>
    function toSomething(mixed $_): Option
        return Option::none();
    $items = [];
    Option::do(function() use ($items) {
        $mapped = [];
        /** @psalm-suppress MixedAssignment */
        foreach ($items as $item) {
            $mapped[] = yield toSomething($item);
        return $mapped;
    PHP Fatal error:  Uncaught Error: Call to a member function isEmpty() on null in /home/app/vendor/whsv26/functional/src/Fp/Functional/Option/Option.php:82
    Stack trace:
    #0 /home/app/run.php(26): Fp\Functional\Option\Option::do()
    #1 {main}
      thrown in /home/app/vendor/whsv26/functional/src/Fp/Functional/Option/Option.php on line 82
    Process finished with exit code 255

    This only happens if no yield has been called in Option::do.

    opened by klimick 1
  • Allow `null` values for `Option`

    Allow `null` values for `Option`

     * Returns value from $array by $path if present
     * @param non-empty-list<string> $path
     * @psalm-pure
    function dotAccess(array $path, array $array): Option
        $key = $path[0];
        $rest = array_slice($path, offset: 1);
        if (empty($rest) && array_key_exists($key, $array)) {
            return Option::of($array[$key]);
        if (array_key_exists($key, $array) && is_array($array[$key])) {
            return dotAccess($rest, $array[$key]);
        return new None();
    $arr = [
        'person' => [
            'name' => 'Jhon',
            'address' => null,
    // Prints Some('Jhon') - good
    print_r(dotAccess(['person', 'name'], $arr));
    // Prints None - not good
    print_r(dotAccess(['person', 'address'], $arr));
    opened by klimick 1
  • Add proveNonEmptyString

    Add proveNonEmptyString

    It would be great if someone implement proveNonEmptyString

    opened by klimick 1
  • Add Either::mapLeft

    Add Either::mapLeft

    Currently there is no way to change left side of the Either.

    Syntactic example where it can be useful:

     * @return Either<ApplicationError, OrderOutput>
    function createOrder(OrderInput $input, OrderService $service): Either
        return $service->create($input)
            ->map(fn(Order $o) => OrderOutput::from($o))
            ->mapLeft(fn(OrderError $e) => ApplicationError::from($e));
            // map concrete domain error to more generic error
    opened by klimick 1
  • Fp\Json\jsonDecode is unsafe

    Fp\Json\jsonDecode is unsafe

    If you run the following piece of code, it will lead to a runtime error:

    use Fp\Functional\Either\Right;
    use Fp\Functional\Either\Left;
    use function Fp\Json\jsonDecode;
    require __DIR__ . '/vendor/autoload.php';
    $decoded = jsonDecode('"kek"')
        ->map(fn(array $val) => array_merge($val, ['lol' => '_']));
    PHP Fatal error:  Uncaught TypeError: {closure}(): Argument #1 ($val) must be of type array, string given, called in /home/php/whsv26/functional/src/Fp/Functional/Either/Either.php on line 83 and defined in /home/php/whsv26/functional/run.php:12
    Stack trace:
    #0 /home/php/whsv26/functional/src/Fp/Functional/Either/Either.php(83): {closure}()
    #1 /home/php/whsv26/functional/run.php(15): Fp\Functional\Either\Either->flatMap()
    #2 {main}
      thrown in /home/php/whsv26/functional/run.php on line 12

    Because json_decode can deserialize literals like numbers, strings, booleans.

    opened by klimick 1
  • v2.0.3(Jun 9, 2021)

    • RegExpMatch function
    • ProveListOfScalar function
    • Option filter method and psalm plugin for this method
    • Semigroup, Monoid interfaces and base instances
    • Validated refactoring
    Source code(tar.gz)
    Source code(zip)
  • v2.0.2(May 29, 2021)

    • Full runtime unit test coverage
    • Option and Either "orElse" method has been added
    • REPL documentation for every method and function
    • CI/CD pipeline: psalm -> unit testing -> unit tests coverage level
    • New function "butLast"
    • Improved type inference
    • Method "getOrElse" can be called with callable fallback value now
    Source code(tar.gz)
    Source code(zip)
Alexander Sv.
Alexander Sv.
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