CSC/ECE 517 Fall 2010/ch1 1e bb
Introduction
This wiki page talks about the the features of functional and object-oriented programming and what are the advantages of mixing functional and object-oriented code.It is intended for people who have basic programming knowledge.
Functional Programming
Functional programming treats computation as the evaluation of mathematical functions and avoids maintaining state and mutable data.
- Functional programming decomposes a problem into a set of functions.Input flows through a set of functions.Ideally, functions only take inputs and produce outputs, and don't have any internal state that affects the output produced for a given input.
- Functional programming breaks apart your problem into small pieces. Small functions are also easier to read and to check for errors, thus debugging is easier.
- Functional Programming discourages the use of variables.
Functional languages include the ML family(Standard ML,OCaml) and Haskell.
An example of functional code in ML to calculate Factorial:
fun factorial (0 : int) : int = 1 | factorial (n : int) : int = n * factorial (n-1)
The above code snippet computes factorial of an integer recursively. In the first line, the fun factorial keyword defines a function. The notation (0: int) can be interpreted as ‘0 is of type int’ and : int =1 means that the default return value is 1 when 0 is passed as an argument.
In the second line, (n: int) sets the argument n to integer. int = n * factorial (n-1) means the return value of recursive computation is an integer.
We can observe here that no additional variables are used here, no state information is maintained and there are no side-effects to any variables.
Object Oriented Programming
Object-oriented programming (OOP) is a programming language model that uses objects which are discrete bundles of functions and procedures, often relating to a particular real-world concept such as a bank account holder or hockey player, together with how they relate to each other.
- Object Oriented Language decomposes a problem into a set of classes which specifies the state and behavior of real world objects
- The class variables maintain state information, while the methods provide functionality
- Inheritance enables the classes to inherit state and behavior of parent class
- Other common features of Object-Oriented Programming include data abstraction, encapsulation, modularity & polymorphism.
Object Oriented languages include Java, Python, C++, Visual Basic .NET Ruby etc.
An example of Object-Oriented code in JAVA to calculate Factorial:
public class Factorial
{
public int fact;
public int factorial(int n)
{
if (n <= 1)
return 1;
else
return n * factorial(n-1);
}
}
The method public int factorial (int n) computes the factorial of variable n. If the value of argument n<=1 then 1 is returned. Otherwise, the statement return n* factorial(n-1) calls the function recursively.
A point to note here is that we can maintain various states of the variable private int fact in the above code. If we create 3 instances of the above class (f1, f2 and f3), then the below code in main can maintain 3 states of the variable private int fact.
public static void main(String argv[])
{
Factorial f1 = new Factorial(); //instance 1
Factorial f2 = new Factorial(); //instance 2
Factorial f3 = new Factorial(); //instance 3
f1.fact = f1.factorial(5); //state 1 of int fact
f2.fact = f2.factorial(9); //state 2 of int fact
f3.fact = f3.factorial(12); //state 3 of int fact
}
Thus object oriented approach can be used to maintain state information of a variable, which is completely opposite to the functional approach.
Mixing functional and object oriented code
Functional programming is a programming paradigm that uses the functions in their real mathematical sense. Functional programming provides powerful features which can be leveraged by a programmer to develop a clean & concise code. Some of the basic features of Functional Programming are:
- Lambda Calculus
- Immutability
- Powerful pattern matching
- Continuations
But at the same time, Object Oriented paradigm is crucial for programming current industrial applications. A large enterprise software is based on object oriented approach because of better modularity in design, easier maintenance and easy extensibility.
Because of individual features of both the programming approaches, many new programming languages enable the programmers to mix both object oriented and functional codes together. While the software design can be based on object oriented approach, its inner functionality can be supported by using functional code.
Using Lambda Calculus inside the Object Oriented code
Lambda calculus is an integral part of functional programming. It is a formal system designed to investigate:
- function definition
- function application
- recursion.
Lambda calculus can be used to define a computable function which maintains no state information. A Lambda function can be passed as an argument to other functions. This demonstrates an important functional fact that the lambda function behaves like a value.
While using Lambda functions, there is another concept called curried functions in which a function reduces the terms and returns another function as a result. In the curried function systems, the result of a function with multiple arguments is expressed as another function. This is a pure functional approach, but Lambdas can be embedded inside the object oriented code so as to make the code more clear, concise and state-less.
The below code in Ruby demonstrates the use of both Functional and Object Oriented Approaches:
class Array
def iterate!(code)
self.each_with_index do |n, i|
self[i] = code.call(n)
end
end
end
array = [1, 2, 3, 4]
array.iterate!(lambda { |n| n ** 2 })
puts array.inspect
The above code calculate the squares of the given numbers of an array. A class called class Array is defined which contains iterate method. This is a pure object oriented approach. The method iterate iterates through 1 to n. Inside the loop:
self[i] = code.call(n)
calls the lambda construct for each array member for computing its square. The statement:
array.iterate!(lambda { |n| n ** 2 })
is a lambda construct with a single argument n. The value of n is squared using n**2 and is returned back to the calling construct. This demonstrates a functional approach in the same code. In the above program, we observe here that the basic functionality of squaring the number was implemented by a functional code, while the basic design of the program is still object-oriented. Functional code can thus be used to fill up important gaps in the object oriented code and provides a way to implement the functionality in a more clear and concise manner.
Programming Languages which support both Object Oriented and Functional code
The solution to a problem can be obtained in an elegant & concise way if functional code supports Object oriented programming. Combining the features of both the approaches can lead to development of efficient and quick solutions of relatively complex problems. This realization has led to the support of functional paradigm in many Object Oriented Programming languages.
Languages like Scala, Clojure, F#, Ruby etc. support both Functional and Object Oriented approaches. Here is a description of some of the most famous “mixed” paradigm languages.
Scala
Scala is a general purpose programming language designed to express common programming patterns in a concise, elegant, and type-safe way. It smoothly integrates features of object-oriented and functional languages, enabling Java and other programmers to be more productive. Code sizes are typically reduced by a factor of two to three when compared to an equivalent Java application.
Scala is object-oriented
Scala is a pure object-oriented language in the sense that every value is an object. Types and behavior of objects are described by classes and traits. Classes are extended by subclassing.
Scala is functional
Scala is also a functional language in the sense that every function is a value. Scala provides a lightweight syntax for defining anonymous functions, it supports higher-order functions, it allows functions to be nested, and supports currying. Scala's case classes and its built-in support for pattern matching model algebraic types used in many functional programming languages.
object objfactorial extends Application {
def factorial(n: Int): Int =
if (n == 0) 1 else n * factorial(n-1)
val f3 = factorial(3); val f4 = factorial(4)
println("3! = " + f3)
println("4! = " + f4)
}
The Application class can be used to quickly turn objects into executable programs. object statement creates an object called objfactorial. This is Object Oriented code. def statement is used to define a function factorial which takes an integer argument and its return type is integer. It is computing the factorial of the given input. This is functional code.
Clojure
Clojure is a general-purpose language which combines the interactive development of a scripting language with an efficient and robust infrastructure for multithreaded programming. It is a dynamic programming language that targets the Java Virtual Machine. It provides easy access to the Java frameworks, with optional type hints and type inference.
Ruby
Ruby is a dynamically typed Object Oriented Language which supports multiple programming paradigms, including functional, object oriented, imperative and reflective. In Ruby, everything is an object,every bit of information and code can have its own properties and actions. However, Ruby’s blocks can be functional. A Ruby programmer can attach a closure to any method, which generates a functional block inside an object oriented code.
Conclusion
Adding some functional programming capabilities within an object-oriented language leads to benefits for object-oriented programming design. Functional Programming offers two facets with regard to functions:
- Purity means mathematical-like functions, without any possibilities of dealing with side-effects.this leads to nice properties, like simpler testing and ready-to-use parallelism.
- First-class citizenship means functions considered as any other values: this leads to better functional granularity design and specific programming techniques.
By mixing both functional and object-oriented code we can reap the advantages of both. It is widely being used in applications nowadays.
References
- Wikipedia - Functional Programming
- Wikipedia - ML (programming language)
- Introduction to Computing - Dickinson College
- Wikipedia - Object Oriented Programming
- More on Object Oriented Programming
- Understanding Ruby Blocks, Procs and Lambdas - Robert Sosinski
- Power of Functional Programming, its Features and its Future
- Mixing Functional and Object Oriented Approaches to Programming in C#
- Scala
- Clojure
- Ruby
- Standard ML