I am still confused about what first-class functions are. If I understand correctly, first-class functions should use one function as an object. Is this correct?
Is this a first-class function?
def this_is_example(myarg1):
return myarg1
def this_is_another_example(myarg):
return this_is_example(myarg) + myarg
this_is_another_example(1)
A first-class function is not a particular kind of function. All functions in Python are first-class functions. To say that functions are first-class in a certain programming language means that they can be passed around and manipulated similarly to how you would pass around and manipulate other kinds of objects (like integers or strings). You can assign a function to a variable, pass it as an argument to another function, etc. The distinction is not that individual functions can be first class or not, but that entire languages may treat functions as first-class objects, or may not.
"First-Class Functions" (FCF) are functions which are treated as so called "First-Class Citizens" (FCC). FCC's in a programming language are objects (using the term "objects" very freely here) which:
Actually, very roughly and simply put, FCF's are variables of the type 'function' (or variables which point to a function). You can do with them everything you can do with a 'normal' variable.
Knowing this, both this_is_another_example(myarg) and this_is_example(myarg1) are First-Class Functions, since all functions are First-Class in certain programming languages.
No. You are talking about higher-order functions -- refer.
First class functions: If a function can be assigned to a variable or passed as object/variable to other function, that function is called as first class function.
Python, JavaScript and C(pointers) support first class functions.
A simple example (in python):
def square(x): return x * x
def cube(x): return x * x * x
def print_result(x, func):
"""recieve a function and execute it and return result"""
return func(x)
do_square = square # assigning square function to a variable
do_cube = cube # assigning cube function to a variable
res = print_result(5, do_square) # passing function to another function
print res
res = print_result(5, do_cube)
print res
This program is just for illustration.
First Class functions in Python:
The “first-class” concept only has to do with functions in programming languages. First-class functions means that the language treats functions as values – that you can assign a function into a variable, pass it around etc. It’s seldom used when referring to a function, such as “a first-class function”. It’s much more common to say that “a language has/hasn’t first-class function support”.So "has first-class functions" is a property of a language.
Properties of first class functions:
So, languages which support values with function types, and treat them the same as non-function values, can be said to have "first class functions".
def pie(r):
def circleArea(d):
return r * (d ** 2)
return circleArea
c = pie(3.14)
print c(2)
Above is an example for first class function in python.
First Class functions in Python
First class objects in a language are handled uniformly throughout. They may be stored in data structures, passed as arguments, or used in control structures. A programming language is said to support first-class functions if it treats functions as first-class objects. Python supports the concept of First Class functions.
Properties of first class functions:
A function is an instance of the Object type.
- You can store the function in a variable.
- You can pass the function as a parameter to another function.
- You can return the function from a function.
- You can store them in data structures such as hash tables, lists, …
Examples illustrating First Class functions in Python
1. Functions are objects: Python functions are first class objects. In the example below, we are assigning function to a variable. This assignment doesn’t call the function. It takes the function object referenced by shout and creates a second name pointing to it, yell.
# Python program to illustrate functions
# can be treated as objects
def shout(text):
return text.upper()
print shout('Hello')
yell = shout
print yell('Hello')
Output:
HELLO
HELLO
# Python program to illustrate functions
# can be passed as arguments to other functions
def shout(text):
return text.upper()
def whisper(text):
return text.lower()
def greet(func):
#storing the function in a variable
greeting = func("Hi, I am created by a function passed as an argument.")
print greeting
greet(shout)
greet(whisper)
Output:
HI, I AM CREATED BY A FUNCTION PASSED AS AN ARGUMENT.
hi, i am created by a function passed as an argument.
#Python program to illustrate functions
#Functions can return another function
def create_adder(x):
def adder(y):
return x+y
return adder
add_15 = create_adder(15)
print add_15(10)
Output:
25
Every function in python is first class, because they can be passed around like any other object.
This is a good example to illustrate Python first-class functions in their classical form: a variable holding a lambda function:
twice = lambda x: 2 * x
d = twice(5)
print(d) # 10
