The Ruby Programming Language

Syntactic Structure

So far, we’ve discussed the tokens of a Ruby program and the characters that make them up. Now we move on to briefly describe how those lexical tokens combine into the larger syntactic structures of a Ruby program. This section describes the syntax of Ruby programs, from the simplest expressions to the largest modules. This section is, in effect, a roadmap to the chapters that follow.

The basic unit of syntax in Ruby is the expression. The Ruby interpreter evaluates expressions, producing values. The simplest expressions are primary expressions, which represent values directly. Number and string literals, described earlier in this chapter, are primary expressions. Other primary expressions include certain keywords such as true, false, nil, and self. Variable references are also primary expressions; they evaluate to the value of the variable.

More complex values can be written as compound expressions:

[1,2,3]                # An Array literal
{1=>"one", 2=>"two"}   # A Hash literal
1..3                   # A Range literal

Operators are used to perform computations on values, and compound expressions are built by combining simpler subexpressions with operators:

1         # A primary expression
x         # Another primary expression
x = 1     # An assignment expression
x = x + 1 # An expression with two operators

Chapter 4 covers operators and expressions, including variables and assignment expressions.

Expressions can be combined with Ruby’s keywords to create statements, such as the if statement for conditionally executing ...