5. Functions

A function lets us wrap up a sequence of statements as a unit that can be called from elsewhere in a program, perhaps multiple times. Functions make it possible to break a big job into smaller pieces that might well be written by different people separated by both time and space. A function hides its implementation details from its users. For all of these reasons, functions are a critical part of any programming language.

We’ve seen many functions already. Now let’s take time for a more thorough discussion. The running example of this chapter is a web crawler, that is, the component of a web search engine responsible for fetching web pages, discovering the links within them, fetching the pages identified by those links, and so on. A web crawler gives us ample opportunity to explore recursion, anonymous functions, error handling, and aspects of functions that are unique to Go.