**''DEFPARAMETER''**

Defines symbol in global scope as parameter. The forms ''DEFPARAMETER'' and ''DEFVAR'' are similar, and both have the purpose to make the LISP program more human-readable. There is no difference between the symbols defined by ''DEFVAR'', ''DEFPARAMETER'' or just with ''SETQ''.

The idea is that the value of symbol introduced with ''DEFPARAMETER'' will not used as changing variable, but as a parameter. If needed, it can be changed, preferably with another ''DEFPARAMETER''.

''DEFPARAMETER'' form needs two arguments, and can have one more optional description string. The first parameter must be a symbol. Symbols from base package (//reserved//), or symbols defined as constants will not be allowed. Second argument is evaluated, and will be bound as the value for the parameter. In case that the symbol is already bound, ''DEFPARAMETER'' will overwrite the value. Third, optional argument is a description string.

<code lisp>
>(defparameter wheels 4 "usual number of wheels")   
WHEELS
</code>

See also: ''DEFVAR'', ''SETQ'', ''DEFCONSTANT''