Programming Crystal

Conventions Used in This Book

The following notation conventions are used throughout the book.

A # => precedes the output or results of executing a code snippet.

p 2 + 2    # => 4

In order to keep code short, we’ll sometimes omit the p, puts or print in the book like this:

2 + 2     # => 4

The Crystal Playground environment (see ​Working with Crystal Playground​) shows the values and types of all expressions, so you don’t need to tell the program explicitly to print. Use p, puts, or print, however, to produce output in another editor or IDE.

Some code files contain lines that compile into an error. This is on purpose because errors can be very educational. Examining these error messages carefully gives you a good indication of what went wrong, ...