In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "We can include other contexts through the use of the include directive."

A block of code is set as follows:

(def numbers (atom []))

(defn adder [key ref old-state new-state]
  (print "Current sum is " (reduce + new-state)))

(add-watch numbers :adder adder)

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

(-> (repeat-obs 5)
    (rx/subscribe prn-to-repl))

;; 5
;; 5

Any command-line input or output is written as follows:

lein run -m sin-wave.server

New terms and important words are shown in bold. Words that you see on the screen, in menus, or dialog boxes, for example, appear in the text like this: "If this was a web application our users would be presented with a web server error such as the HTTP code 500 – Internal Server Error."