As you have probably already noticed, Scheme's syntax is Lisp-like.
All function applications are in fully-parenthesized prefix form.
While some find this sort of syntax unwieldy, it has the advantage
that Scheme forms are actually lists which can be easily manipulated
with standard list primitives. The libscheme library supports
the defmacro special form that can be used by end users to
create new special forms. A special form is a form that is evaluated
by special rules. For example, the if special form only
evaluates its ``then'' condition if its test expression evaluates to
true, otherwise it evalutes its ``else'' expression.
These macros are much more powerful than the simple token-based substitution macros provided by languages like C.