Editing Reduce (computer algebra system) (section)

=== Statements and expressions ===
Because REDUCE inherits Lisp semantics, all programming constructs have values. Therefore, the only distinction between statements and expressions is that the value of an expression is used but the value of a statement is not. The terms ''statement'' and ''expression'' are interchangeable, although a few constructs always return the Lisp value <code>nil</code> and so are always used as statements.

There are two ways to group several statements or expressions into a single unit that is syntactically equivalent to a single statement or expression, which is necessary to facilitate [[structured programming]]. One is the <code>begin</code>...<code>end</code> construct inherited from ALGOL 60, which is called a ''block'' or ''compound'' statement. Its value is the value of the expression following the (optional) keyword <code>return</code>. The other uses the bracketing syntax <code><<</code>...<code>>></code>, which is called a ''group'' statement. Its value is the value of the last (unterminated) expression in it. Both are illustrated below in the [[#Procedural programming|procedural programming example]] below.