Broadly speaking, there are two things of interest, functions and variables. A single variable stores a value, collections of variables can store many different values. Functions contain code that may read the value of variables, do some processing, and change the value of variables in the process.
The first thing to mention is that some lines in a Nano program dont do anything at all. They are ignored completely by the lanauge and are only there to help the programmer. These are blank lines and lines known as comments.
# im a comment, but above and below are blank lines
Everything in the example given below is ignored by the language. The use of blank lines and comments allow the programer to keep notes about their program to let others or themselves know how it works. We will see comments used below to hilight interesting parts in the examples.
Functions contain code to perform an number of operations, some of which may be to run other functions as well.
Within a function code will be processed a line at a time, one by one. When one line has been fully processed, the next line below it will start to run.
As we will see, the order in which lines run can be changed using if and while statements.
An example of a function is given:
function a_name()
return 1
end
Starting a line with the keyword function tells Nano that we want to define a function. Imediately following that comes the functions name, in this case a_name.
After a functions name comes two parenthesis (), this is where we can specify the inputs to a function, known as arguments. For now we will leave them empty, indicating that this function takes no inputs.
To mark the end of a function, on the last line we can see the end keyword. All constructs in Nano that span multiple lines can be ended with the end keyword as we will see.
The middle line return 1 is known as a statement, in this case a return statement. When a statement is run, it will effect the state of the program. We will learn more about the return statement later.
All Nano programs start by running the function named main. Lets look at how one function can run another function, a process known as calling a function.
function func_1()
# its empty
end
function main()
# here we `call` func_1
func_1()
end
In this case, there are two functions func_1 and main. func_1 is empty, which is to say it can be run but it will do nothing.
The function main contains a statement known as a function call, in this case it will instruct func_1 to run.
After func_1 has run, main will continue to run, however in this case there are no more statements so main will finish.
When the function main finishes, the program will also end.
Lets look at a more complicated example of functions with inputs and outputs.
function func_2(an_arg)
return an_arg
end
function main()
func_2(3)
end
In this example we can see that the function func_2 has one input named an_arg.
When we look at main we can see it calls func_2 and gives it an input value, in this case 3.
The program starts by running main, the first action being to call func_2 with one input.
At this point main waits while func_2 runs. Inside of func_2 there is one statement, the
return statement, which in this case is returning the input an_arg back to whoever called it.
In this case the value 3 was passed as input to func_2 who then returned it back to main.
The value 3 returned back to main is not used, and then the function ends and the program finishes.