4.8. FuncProg Referential Transparency¶
Value of a variable in a functional program never changes once defined
This eliminates any chances of side effects
Any variable can be replaced with its actual value at any point of execution 2
Any variable can be replaced with its actual value at any point of execution 2. This is known as referential transparency. It ensures that the same language expression gives the same output. 1
Variables, once defined in a functional programming language, aren't allowed to change the value that they hold. However, we can create a new variable. The immutable nature of variables helps preserve the state throughout the program. Assignment statements are discouraged in functional programming. For storing additional values in a program developed using the functional paradigm, new variables must be defined. The state of a variable in such a program is constant at any moment in time. 1
Referential transparency eliminates the slightest chances of any undesired effects, as any variable can be replaced with its actual value at any point during the program execution. 1
Bad:
>>> a = 1
>>> a += 2
Good:
>>> a = 1
>>> b = a + 2
4.8.1. Use Case - 0x01¶
>>> def add(a,b):
... return a + b
>>>
>>>
>>> x = 1
>>> y = 2
>>>
>>> add(x,y)
3
>>> add(1,y)
3
>>> add(x,2)
3
>>> add(1,2)
3