README

Installation

Supported installation method is via composer:

composer require fp4php/functional-psalm-plugin --dev

Usage

To enable the plugin, add the Fp\PsalmPlugin\FunctionalPlugin class to your psalm configuration using psalm-plugin binary as follows:

php vendor/bin/psalm-plugin enable fp4php/functional-psalm-plugin

Features

• filter

Plugin add type narrowing for filtering.

Fp\Functional\Option\Option::filter:

<?php

declare(strict_types=1);

use Fp\Functional\Option\Option;

/**
* @return Option<int|string>
*/
function getOption(): Option
{
  // ...
}

// Narrowed to Option<string>

/** @psalm-trace $result */
$result = getOption()->filter(fn($value) => is_string($value));

Fp\Collections\ArrayList::filter (and other collections with filter method):

<?php

declare(strict_types=1);

use Fp\Collections\ArrayList;

/**
* @return ArrayList<int|string>
*/
function getArrayList(): ArrayList
{
  // ...
}

// Narrowed to ArrayList<string>

/** @psalm-trace $result */
$result = getArrayList()->filter(fn($value) => is_string($value));

Fp\Functional\Either\Either::filterOrElse:

<?php

declare(strict_types=1);

use TypeError;
use ValueError;
use Fp\Functional\Either\Either;

/**
* @return Either<ValueError, int|string>
*/
function getEither(): Either
{
  // ...
}

// Narrowed to Either<TypeError|ValueError, string>
getEither()->filterOrElse(
  fn($value) => is_string($value),
  fn() => new TypeError('Is not string'),
);

Fp\Collection\filter:

<?php

declare(strict_types=1);

use function Fp\Collection\filter;

/**
* @return list<int|string>
*/
function getList(): array
{
  // ...
}

// Narrowed to list<string>
filter(getList(), fn($value) => is_string($value));

Fp\Collection\first and Fp\Collection\last:

<?php

declare(strict_types=1);

use function Fp\Collection\first;
use function Fp\Collection\last;

/**
* @return list<int|string>
*/
function getList(): array
{
  // ...
}

// Narrowed to Option<string>
first(getList(), fn($value) => is_string($value));

// Narrowed to Option<int>
last(getList(), fn($value) => is_int($value));

For all cases above you can use first-class callable syntax:

<?php

declare(strict_types=1);

use function Fp\Collection\filter;

/**
* @return list<int|string>
*/
function getList(): array
{
  // ...
}

// Narrowed to list<string>
filter(getList(), is_string(...));

• fold

Is too difficult to make the fold function using type system of psalm. Without plugin Fp\Collection\fold and collections fold method has some edge cases. For example: https://psalm.dev/r/b0a99c4912

Plugin can fix that problem.

• ctor

PHP 8.1 brings feature called first-class callable. But that feature cannot be used for class constructor. Fp\Callable\ctor can simulate this feature for class constructors, but requires plugin for static analysis.

<?php

use Tests\Mock\Foo;

use function Fp\Callable\ctor;

// Psalm knows that ctor(Foo::class) is Closure(int, bool, bool): Foo 
test(ctor(Foo::class));

/**
* @param Closure(int, bool, bool): Foo $makeFoo
*/
function test(Closure $makeFoo): void
{
  print_r($makeFoo(42, true, false));
  print_r(PHP_EOL);
}

• sequence

Plugin brings structural type inference for sequence functions:

<?php

use Fp\Functional\Option\Option;

use function Fp\Collection\sequenceOption;
use function Fp\Collection\sequenceOptionT;

function getFoo(int $id): Option
{
  // ...
}

function getBar(int $id): Option
{
  // ...
}

/**
* @return Option<array{foo: Foo, bar: Bar}>
*/
function sequenceOptionShapeExample(int $id): Option
{
  // Inferred type is: Option<array{foo: Foo, bar: Bar}> not Option<array<'foo'|'bar', Foo|Bar>>
  return sequenceOption([
      'foo' => getFoo($id),
      'bar' => getBar($id),
  ]);
}

/**
* @return Option<array{Foo, Bar}>
*/
function sequenceOptionTupleExample(int $id): Option
{
  // Inferred type is: Option<array{Foo, Bar}> not Option<list<Foo|Bar>>
  return sequenceOptionT(getFoo($id), getBar($id));
}

• assertion

Unfortunately @psalm-assert-if-true/@psalm-assert-if-false works incorrectly for Option/Either assertion methods: https://psalm.dev/r/408248f46f

Plugin implements workaround for this bug.

• N-combinators

Psalm plugin will prevent calling *N combinator in non-valid cases:

<?php

declare(strict_types=1);

use Fp\Functional\Option\Option;
use Tests\Mock\Foo;

/**
* @param Option<array{int, bool}> $maybeData
* @return Option<Foo>
*/
function test(Option $maybeData): Option
{
  /*
   * ERROR: IfThisIsMismatch
   * Object must be type of Option<array{int, bool, bool}>, actual type Option<array{int, bool}>
   */
  return $maybeData->mapN(fn(int $a, bool $b, bool $c) => new Foo($a, $b, $c));
}

• proveTrue

Implementation assertion effect for Fp\Evidence\proveTrue (like for builtin assert function):

<?php

use Fp\Functional\Option\Option;

function getIntOrString(): int|string
{
  // ...
}

Option::do(function() {
  $value = getIntOrString();
  yield proveTrue(is_int($value));

  // here $value narrowed to int from int|string
});

• toEither

Inference for Fp\Functional\Separated\Separated::toEither:

<?php

use Fp\Collections\HashSet;
use Fp\Collections\ArrayList;
use Fp\Functional\Either\Either;
use Fp\Functional\Separated\Separated;

/**
* @param Separated<ArrayList<int>, ArrayList<string>> $separated
* @return Either<ArrayList<int>, ArrayList<string>>
*/
function separatedArrayListToEither(Separated $separated): Either
{
  return $separated->toEither();
}

/**
* @param Separated<HashSet<int>, HashSet<string>> $separated
* @return Either<HashSet<int>, HashSet<string>>
*/
function separatedHashSetToEither(Separated $separated): Either
{
  return $separated->toEither();
}

• partitionT

Plugin infers each list type from predicates of partitionT:

<?php

declare(strict_types=1);

use Tests\Mock\Foo;
use Tests\Mock\Bar;
use Tests\Mock\Baz;

use function Fp\Collection\partitionT;

/**
* @param list<Foo|Bar|Baz> $list
* @return array{list<Foo>, list<Bar>, list<Baz>}
*/
function testExhaustiveInference(array $list): array
{
  return partitionT($list, fn($i) => $i instanceof Foo, fn($i) => $i instanceof Bar);
}

• filterNotNull

Plugin turns all nullable keys to possibly undefined keys:

<?php

declare(strict_types=1);

use function Fp\Collection\filterNotNull;

/**
* @param array{name: string, age: int|null} $shape
* @return array{name: string, age?: int}
*/
function example(array $shape): array
{
   return filterNotNull($shape);
}