Fixes liftM2 implementation #97 (#100)

* Fixes #97 but breaks FreeCalculatorTest.php * old liftM2 to bindM2 and correct implementation * cs fix

Author: ilario-pierbattista

example/EitherMonadTest.php

@@ -19,7 +19,7 @@ class EitherMonadTest extends \PHPUnit\Framework\TestCase
 {
  public function test_it_should_concat_content_of_two_files_only_when_files_exists()
  {
- $concatF = f\liftM2(function ($first, $second) {
+ $concatF = f\bindM2(function ($first, $second) {
  return $first . $second;
  });
 

example/FreeCalculatorTest.php

@@ -11,7 +11,7 @@
 use Widmogrod\Primitive\Stringg;
 use Widmogrod\Useful\PatternMatcher;
 use function Widmogrod\Functional\compose;
-use function Widmogrod\Functional\liftM2;
+use function Widmogrod\Functional\bindM2;
 use function Widmogrod\Monad\Free\foldFree;
 use function Widmogrod\Monad\Free\liftF;
 use function Widmogrod\Useful\match;
@@ -161,7 +161,7 @@ public function patternMatched(callable $fn)
 
 function sum(MonadFree $a, MonadFree $b): MonadFree
 {
- return liftM2(function ($a, $b) {
+ return bindM2(function ($a, $b) {
  return liftF(new Sum($a, $b, Pure::of));
  }, $a, $b);
 }
@@ -177,7 +177,7 @@ function int(int $int): MonadFree
 
 function mul(MonadFree $a, MonadFree $b): MonadFree
 {
- return liftM2(function ($a, $b) {
+ return bindM2(function ($a, $b) {
  return liftF(new Multiply($a, $b, Pure::of));
  }, $a, $b);
 }

src/Functional/functions.php

@@ -4,12 +4,12 @@
 
 namespace Widmogrod\Functional;
 
-use Widmogrod\Common\ValueOfInterface;
 use FunctionalPHP\FantasyLand\Applicative;
 use FunctionalPHP\FantasyLand\Foldable;
 use FunctionalPHP\FantasyLand\Functor;
 use FunctionalPHP\FantasyLand\Monad;
 use FunctionalPHP\FantasyLand\Traversable;
+use Widmogrod\Common\ValueOfInterface;
 use Widmogrod\Primitive\Listt;
 use Widmogrod\Primitive\ListtCons;
 
@@ -379,7 +379,7 @@ function reThrow(\Exception $e)
 const liftM2 = 'Widmogrod\Functional\liftM2';
 
 /**
- * Lift result of transformation function , called with values from two monads.
+ * Lift result of transformation function, called with values from two monads.
  *
  * liftM2 :: Monad m => (a -> b -> c) -> m a -> m b -> m c
  *
@@ -397,6 +397,39 @@ function liftM2(
  callable $transformation = null,
  Monad $ma = null,
  Monad $mb = null
+) {
+ return curryN(
+ 3,
+ function (
+ callable $transformation,
+ Monad $ma,
+ Monad $mb
+ ) {
+ return bindM2(function ($a, $b) use ($transformation, $mb): Monad {
+ return $mb::of($transformation($a, $b));
+ }, $ma, $mb);
+ }
+ )(...func_get_args());
+}
+
+/**
+ * @var callable
+ */
+const bindM2 = 'Widmogrod\Functional\bindM2';
+
+/**
+ * bindM2 :: Monad m => (a -> b -> m c) -> m a -> m b -> m c
+ *
+ * @param callable $transformation
+ * @param Monad $ma
+ * @param Monad $mb
+ *
+ * @return Monad|\Closure
+ */
+function bindM2(
+ callable $transformation = null,
+ Monad $ma = null,
+ Monad $mb = null
 ) {
  return curryN(
  3,

test/Functional/LiftM2Test.php

@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace test\Functional;
+
+use FunctionalPHP\FantasyLand\Monad;
+use Widmogrod\Functional as f;
+use Widmogrod\Monad\Either;
+use Widmogrod\Monad\Maybe;
+
+class LiftM2Test extends \PHPUnit\Framework\TestCase
+{
+ /**
+ * @dataProvider monadsProvider
+ */
+ public function test_it_should_lift2M(
+ Monad $ma,
+ Monad $mb,
+ callable $transformation,
+ string $expectedFQCN,
+ $expectedExtracted = null
+ ) {
+ $mc = f\liftM2($transformation, $ma, $mb);
+
+ $this->assertInstanceOf($expectedFQCN, $mc);
+
+ if ($expectedExtracted !== null) {
+ $this->assertSame($expectedExtracted, f\valueOf($mc));
+ }
+ }
+
+ public function monadsProvider()
+ {
+ $sumIntegers = static function (int $a, int $b) {
+ return $a + $b;
+ };
+
+ return [
+ 'maybe all nothing' => [
+ Maybe\nothing(),
+ Maybe\nothing(),
+ $sumIntegers,
+ Maybe\Nothing::class
+ ],
+ 'maybe first just' => [
+ Maybe\just(1),
+ Maybe\nothing(),
+ $sumIntegers,
+ Maybe\Nothing::class
+ ],
+ 'maybe second just' => [
+ Maybe\nothing(),
+ Maybe\just(2),
+ $sumIntegers,
+ Maybe\Nothing::class
+ ],
+ 'maybe all just' => [
+ Maybe\just(1),
+ Maybe\just(2),
+ $sumIntegers,
+ Maybe\Just::class,
+ 3
+ ],
+ 'either all left' => [
+ Either\left('a'),
+ Either\left('b'),
+ $sumIntegers,
+ Either\Left::class
+ ],
+ 'either first right' => [
+ Either\right(3),
+ Either\left('b'),
+ $sumIntegers,
+ Either\Left::class
+ ],
+ 'either second right' => [
+ Either\left('a'),
+ Either\right(4),
+ $sumIntegers,
+ Either\Left::class
+ ],
+ 'either all right' => [
+ Either\right(3),
+ Either\right(4),
+ $sumIntegers,
+ Either\Right::class,
+ 7
+ ]
+ ];
+ }
+}