4.12.1.1 Function type and 4.12.1.2 First-class object

Question 1

What is a function?

Answer 1

a rule that, for each element in some set A of inputs, assigns an output chosen from set B
A -> B where A is the domain and B is the codomain
A is the argument type, a value passed
B is the result type
some functions are predefined, some are user defined

Question 2

What is the domain / co-domain?

Answer 2

The domain is a set from which the function’s input values are chosen.
The co-domain is a set from which the function’s output values are chosen. Not all of the co-domain’s members need to be outputs.

Question 3

What is a first class object?

Answer 3

First-class objects (or values) are objects which may:
appear in expressions
be assigned to a variable
be assigned as arguments
be returned in function calls
e.g  integers, floating-point values, characters and strings

Question 4

Why are functions first class objects?

Answer 4

It can be an argument to another function as well as the result of a function call.