Pure function:
A function is said to be pure if a function produces the same result when evaluating with same argument(s). Function result should not depend on hidden values or state that may change the result of program. We can say that a pure function depends only on its argument(s). Example Sin(x), Sizeof()...etc
Reactive Systems:
Reactive systems are systems whose role is to maintain an ongoing interaction with their environment at specified rate rather than produce some final value upon termination." Usually all embedded systems and industrial "Real time" systems are reactive in nature. The main feature of these systems are:
- They involve concurrency.
- They are usually deterministic.
- They are generally made of both H/W and S/W.
Referential Transparency:
Referential transparency, a term commonly used in functional programming, means that a function/method invocation can be replaces by its return value without changing algorithm or program semantics. Ex F(x)=x +1 in this function for a given value of x say 5, it can be replaced by 6 easily. This can only be true when
- function simply compute a value.
- function is independent of temporal context and has no side effect.
The main advantage of referential transparency is that it makes it much easier to reason about programs, and to apply program transformations... including optimizations and partial evaluations at compile-time (since if a computation has no side-effects, then it doesn't matter whether you calculate it now or later).
Referential Opaqueness:
This concept is just opposite of referential transparent. Functions can't be replaced by their value because they depend on external things. For example if a function getinput() is reading from a file or keyboard then it's output can not be predict because file can be changed or user can enter any char/word/sentence.
Another example is
int a= 10; //global variable
func(int x)
{
return x+a;
}
ny
This function will not always add 10 to given value of x because as a is global it can be changed by other function or assignment.
