Remember the writing y = F(x) ? I think you do! You have certainly encountered while studying math. Programming has a very similar concept.

We can loosely define a function as a group of instructions enclosed in a box to which a name is assigned; also a type and possible arguments which are passed to it. The box will output a value which will depend from the functions (what is inside the box).

In order to build a function using the programming language, it is necessary to give a few fundamental information about the interpreter. These information are the start and end of a group of instructions (BLOCK) which are the function, the name and type of the function, input argument and their types.