Editing Common Lisp (section)

==Syntax==
Common Lisp is a dialect of Lisp. It uses [[S-expression]]s to denote both code and data structure. Function calls, macro forms and special forms are written as lists, with the name of the operator first, as in these examples:

<syntaxhighlight lang="lisp">
 (+ 2 2)           ; adds 2 and 2, yielding 4. The function's name is '+'. Lisp has no operators as such.
</syntaxhighlight>
<syntaxhighlight lang="lisp">
 (defvar *x*)      ; Ensures that a variable *x* exists,
                   ; without giving it a value. The asterisks are part of
                   ; the name, by convention denoting a special (global) variable. 
                   ; The symbol *x* is also hereby endowed with the property that
                   ; subsequent bindings of it are dynamic, rather than lexical.
 (setf *x* 42.1)   ; Sets the variable *x* to the floating-point value 42.1
</syntaxhighlight>
<syntaxhighlight lang="lisp">
 ;; Define a function that squares a number:
 (defun square (x)
   (* x x))
</syntaxhighlight>
<syntaxhighlight lang="lisp">
 ;; Execute the function:
 (square 3)        ; Returns 9
</syntaxhighlight>
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<syntaxhighlight lang="lisp">
 ;; The 'let' construct creates a scope for local variables. Here
 ;; the variable 'a' is bound to 6 and the variable 'b' is bound
 ;; to 4. Inside the 'let' is a 'body', where the last computed value is returned.
 ;; Here the result of adding a and b is returned from the 'let' expression.
 ;; The variables a and b have lexical scope, unless the symbols have been
 ;; marked as special variables (for instance by a prior DEFVAR).
 (let ((a 6)
       (b 4))
   (+ a b))        ; returns 10
</syntaxhighlight>