callout defining function

[SamPenrose]

To address Issue #26

[SamPenrose]

p.s., I also wrote this (per the issue), but I don't actually think its an improvement over just getting into the example:

Functions take the form:

function_name <- function( parameters ) function_body

where:

• function_name what the programmer has decided to call her function
• parameters is an optional list of named values the function accepts as input
• function_body is a sequence of expressions

You invoke a function by entering its name followed by the call operator, a pair of parentheses: "()". If the function takes parameters, they go inside the parentheses. R will then execute the function's body, expression by expression. If you assign the result of the function to a variable:

x = some_function('some', 'parameters')

then, when the function finishes executing, whatever it returns will be stored in that variable. By default, R functions return the last evaluated expression. Many functions use the return keyword to send a specific object back to the caller.

[aammd]

I really like this Callout! I made a few line notes.

I have pretty mixed feelings about this "imitation syntax" approach that I've seen sometimes:

function_name <- function( parameters ) function_body

Because it doesn't really resemble actual syntax (ie no {), I'm not sure it doesn't generate more confusion than it solves. But that is just an hypothesis

[sritchie73]

I think its a really good idea to have this callout: I'd even suggest putting it in the very first topic after the first instance where an instructor calls a function.

I'm also not a fan of the "imitation syntax". Novices seem to struggle with pseudocode, its too abstract for them to understand, especially since they've been hammered with lots of new concepts.

[hdashnow]

I think showing the general form of a function is pretty important. But I agree pseudocode can be confusing for beginners. How about something like this? It's still very general, but at least the code would run.

Functions take the form:

function_name <- function( input ) {
    result <- input + 1 # The body of the function. 
    return( result ) # Optional return statement
}

[sritchie73]

I like it!

[aammd]

I really prefer this. Now we have a function that is instructive for beginners, while not being distressing to people who already write functions. I will resolve whatever conflicts (!) we have here and merge this.