How can I define cas function of an operator(mathematical term)?

[Aleksandr94]

Thank you for replies!
There is one issue with answers you gave. I most practical cases functions are multivariable. In most cases we don't know the name of variable. So I don't know wether it will be x or other variable. Say l asked this question with intention to define normalisation operator for wavefunctions. I also want to define several other operators like various Hamiltonian operators and so on. So I started with this baby example of indefinite integral. To solve this question I should be able to solve at least any arbitrary integral from CAS. So we stopped there.
So I am asking to help me construct user defined cas function for an mathematical operator (say integration), where we can insert any arbitrary variables.
I tried this:
#CAS
MYINT(f,x):=
BEGIN
RETURN int(f,x);
END;
#end

So I tried this new cas function in CAS mode
MYINT(y^2,y)
And I have obtained this:
Int(f(x)dx)