About the Extension: Think about the concept of '+', you can '+' integers, rational numbers, matrix, etc. There possibly thousands of kinds of things that coul

About the Extension: Think about the concept of '+', you can '+' integers, rational numbers, matrix, etc. There possibly thousands of kinds of things that could be '+'-ed. (Actually, this concept is called monoid) Your job is to implement the abstract idea of '+' (the operator itself without specific meaning) and the integer implementation for '+'. Then you can compile publish your package to a jar, dll or any other form of package other people can download. Everyone, possibly thousands of people can download this package and extend and use the exact same '+' from you, for their own datatype without modifying your code or recompiling your package. At last, 99 out of 100 this could be over-engineering for most of the languages like Java. But for language like Haskell have a feature named type classes, make this almost no-brainer, so it would become 5 out 10 this could be over-engineering in Haskell because the cost and mental overhead are reduced.