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2017 © Pedro Peláez
A PHP implementation of Haskell's Maybe monad
, (*1)
To deal with computations that may fail.
A port of Haskell's Data.Maybe module for PHP > 5.4., (*2)
You can install via Composer., (*3)
composer require haskellcamargo/php-maybe-monad
use HaskellCamargo\Maybe;
Maybe\Maybe(@$_GET["username"])->bind(function($user)) {
echo "Welcome, $user. You're logged in!";
});
$userAge = Maybe\Maybe(null)->fromMaybe(0); // => 0
$userAge = Maybe\Maybe(19)->fromMaybe(0); // => 19
A Maybe type encapsulates an optional value. A value of type Maybe a
either contains a value of type a (represented as Just a), or it is empty
(represented as Nothing). Using Maybe is a good way to deal with errors
or exceptional cases without resorting to drastic measures such as
Exception.
The Maybe type is also a monad. It is a simple kind of error monad, where
all errors are represented by Nothing. A richer error monad can be built
using the Either type., (*4)
Equivalent to Haskell's >>= operator. Its first argument is a value in
a monadic type, its second argument is a function that maps from the
underlying type of the first argument to another monadic type, and its
results is in that other monadic type., (*5)
$age = Maybe\Maybe(null)->bind(function($x) {
return 10;
}); // => Nothing
$age = Maybe\Maybe(10)
->bind(function($x) {
return $x + 10; // => Just(20);
})
->bind(function($x) {
return $x + 20; // => Just(40);
})->fromJust(); // => 40
Extracts the element out of a Just and returns an error if its argument
is Nothing., (*6)
Maybe\Maybe("Foo")->fromJust(); // => "Foo"
Maybe\Maybe(null)->fromJust(); // => Exception: Cannot cal fromJust() on Nothing
Takes a Maybe value and a default value. If the Maybe is Nothing, it
returns the default values; otherwise, it returns the value contained in
the Maybe., (*7)
Maybe\Maybe(10)->fromMaybe(5); // => 10 Maybe\Maybe(null)->fromMaybe(5); // => 5
Returns true if its argument is of the form Just _., (*8)
Maybe\Maybe(10)->isJust(); // => true Maybe\Maybe(null)->isJust(); // => false
Returns true if its argument is of the form Nothing., (*9)
Maybe\Maybe(10)->isNothing(); // => false Maybe\Maybe(null)->isNothing(); // => true
Takes a default value, a function and, of course, a Maybe value. If the
Maybe value is Nothing, the function returns the default value.
Otherwise, it applies the function to the value inside the Just and
returns the result., (*10)
$just = Maybe\Maybe(10);
$nothing = Maybe\Maybe(null);
$just->maybe(40, function($num) {
return $num + 15;
}); // => 25
$nothing->maybe(40, function($num) {
return $num + 15;
}); // => 40
Returns an empty list when given Nothing or a singleton list when not
given Nothing., (*11)
Maybe\Maybe(10)->toList(); // => [10] Maybe\Maybe(null)->toList(); // => []
Made with :heart: by Marcelo Camargo and Reinaldo Rauch, (*12)
MIT, (*13)
A PHP implementation of Haskell's Maybe monad
MIT
A PHP implementation of Haskell's Maybe monad
MIT