You are correct. "object-function" is basically like in Javascript: It's an object (having members) and an executable body. The colons are a shorthand for function call. ie myfunc()

In Copper, variables only store functions. This separates routine from data so you never end up with null pointer errors like in languages that have Any Types or pointers. Functions can return data, so you end up having function calls everywhere. a=5 is basically a={ret(5)}

In your above example the correct first line would be: adder = [a b] { ret(+(a: b:)) }

Parameters to a function are those that are not assigned data, whereas members are: add = [Param, Member=10) { ret(+(Param: this.Member:)) }

Now you can probably see what's wrong with your third line.