Plotting the sine function in the previous section was a bit
cumbersome. As an alternative we can use the function
` plot-function` to plot a function of one
argument over a specified range. We can plot the sine function using
the expression

(plot-function (function sin) (- pi) pi)

The expression ` (function sin)` is needed to extract the
function associated with the symbol ` sin`. Just using
` sin` will not work. The reason is that a symbol in Lisp can
have both a * value*, perhaps set using ` def`, and a *
function definition* at the same time.
This may seem a bit cumbersome at first, but it has one
great advantage: Typing an innocent expression like

(def list '(2 3 4))will not destroy the

Extracting a function definition from a symbol is done almost as often as quoting an expression, so again a simple shorthand notation is available. The expression

#'sinis equivalent to the expression

(plot-function #'sin (- pi) pi).

Tue Jan 21 15:04:48 CST 1997