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The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq
. For example,
(setq x '(a b))
gives the variable x
the value (a b)
. Note that
setq
does not evaluate its first argument, the name of the
variable, but it does evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the symbol by itself as an expression. Thus,
x ⇒ (a b)
assuming the setq
form shown above has already been executed.
If you do another setq
, the new value replaces the old one:
x ⇒ (a b)
(setq x 4) ⇒ 4
x ⇒ 4