PHPrelude

Functional Programming Library for PHP

This library provides a functional-programming core library: Endofunk, that adds many of the data types needed to employ a functional programming style in your codebase; more data types will be added in due course.

Functional Data Types

The following is a list of the functional data types included in Endofunk.

Type	Overview
Identity	The Identity type is a trivial type to access functor, monad, applicative functor, etc. algebras.
Maybe	The 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)
Either	The Either type encapsulates a logical disjunction of two possibilities: either Left or Right.
Result	The Result type is similar to the Either type except that the left disjunction is fixed to capture of a PHP Exception.
Validation	The Validation data type is isomorphic to Either, but has an instance of Applicative that accumulates on the error side.
Reader	The Reader type (also called the Environment monad). Represents a computation, which can read values from a shared environment, pass values from function to function, and execute sub-computations in a modified environment.

All types support Functor, Applicative Functor and Monad; with monadic lifters, applicative lifters, and Kleisli monadic composition.

Functional Prelude

The base prelude combinators, e.g. curry, k-combinator, etc... are for the most part a copy of the Vector PHP FP Library developed by joseph-walker. The code for Vector has however been fully integrated into this framework with a few changes to better fit in with the operation of the monadic data types; meaning there is no dependency on Vector only PHPrelude.

A few Examples:

Currying

...is essentially free with all functions that have the Module extension.

$addOne = Arrays::map(function($a) { return $a + 1; });
$addOne([1, 2, 3]); // [2, 3, 4]

Composition

$addSix = Lambda::compose(Math::add(4), Math::add(2));
$addSix(4); // 10;

$f = Lambda::compose(Strings::toUppercase(), Strings::trim());
$v = Identity::of("hello ")
  ->map($f)
  ->Match(function ($v) {
    echo Strings::log("Identity", $v);
});
 
// -------------------------------------------------------------- Identity ----
// string(5) "HELLO"

Kleisli Composition

$incrementM = function ($v) {
  return Identity::of($v + 1);
};

$squareM = function ($v) {
  return Identity::of($v * $v);
};

$incsquare = Identity::compose($incrementM, $squareM);

Identity::of(2)
  ->bind($incsquare)
  ->Match(function ($v) {
    echo Strings::log("Identity", $v);
  });
 
// -------------------------------------------------------------- Identity ----
// int(9)

Applicative Functor - Lazy Application

$g = function (string $name, string $surname): string {
  return $name . ' ' . $surname;
};
$gc = Module::curry($g);

Identity::of($gc)
  ->fapply(Identity::of("Jack"))
  ->fapply(Identity::of("Sprat"))
  ->Match(function ($v) {
    echo Strings::log("Identity", $v);
});

\\ ------------------------------------------------------- Identity ----
\\ string(10) "Jack Sprat"

Applicative Functor - Lifter

LiftA(x) supports arities from 1 to 9.

$g = function (string $name, string $surname): string {
  return $name . ' ' . $surname;
};

Identity::liftA2($g, Identity::of("Jack"), Identity::of("Sprat")) // liftA(x) auto currys the function
  ->Match(function ($v) {
    echo Strings::log("Identity", $v);
});

\\ ------------------------------------------------------- Identity ----
\\ string(10) "Jack Sprat"

Result Monad wrapping callable in Try/Catch

class SQL extends Module {

  protected static function __connect(string $dsn, string $database, string $host, string $username, string $password): Result {
    return Result::try (function () use ($dsn, $database, $host, $username, $password) {
      return new PDO("$dsn:dbname=$database;host=$host", $username, $password);
    });
  }

  protected static function __query($sql): callable {
    return function ($conn) use ($sql) {
      return Result::try (function () use ($conn, $sql) {
        $result = $conn->query($sql)->fetchAll(PDO::FETCH_ASSOC);
        if (!$result) {
          throw new Exception($mysqli->error0, $severity, $file, $line);
        }
        return [$conn, $result];
      });
    };
  }

  protected static function __close(): callable {
    return function ($conn) {
      return Result::try (function () use ($conn) {
        $conn[0] = null;
        return $conn[1];
      });
    };
  }
}

Usage example of Result based SQL PDO monadic functions

SQL::connect("mysql", "sakila", "127.0.0.1", "username", "password")
  ->bind(SQL::query("call sakila.SP_actors()"))
  ->bind(SQL::close())
  ->match(function ($value) {
    echo json_encode($value) . "\n";
  }, function ($error) {
    echo $error . "\n";
  });
 
// [{"actor_id":"1","first_name":"PENELOPE","last_name":"GUINESS","last_update":"2006-02-15 04:34:33"},
// ...
// ...
// {"actor_id":"200","first_name":"THORA","last_name":"TEMPLE","last_update":"2006-02-15 04:34:33"}]

Usage example of Result based Exception trap

$f = function () {
  throw new Exception("Value must be 1 or below");
  return 1;
};

Result::try ($f)
  ->Match(function ($v) {
     echo Strings::log("Result", $v);
});

// ------------------------------------------------------- Result ----
// string(113) "Error Message: Value must be 1 or below
// Exception code: 0
// Line No: 59
// Filename: /Users/JackSprat/Documents/web/index.php"

endofunk/PHPrelude