`functor', `args', `funargs'
----------------------------

functor(FUNC)
     :: Functor of function form FUNC.

args(FUNC)
     :: List of arguments of function form FUNC.

funargs(FUNC)
     :: `cons(functor(FUNC),args(FUNC))'.

RETURN
     `functor()' : indeterminate, `args()', `funargs()' : list

FUNC
     function form

   * See *Note vtype:: for function form.

   * Extract the functor and  the arguments of function form FUNC.

   * Assign a program variable, say `F', to the functor obtained by
     `functor()'.  Then, you can type (`*F')(x) (, or (`*F')(x,y,...)
     depending on the arity,) to input a function form with argument x.

     [0] functor(sin(x));
     sin
     [0] args(sin(x));
     [x]
     [0] funargs(sin(3*cos(y)));
     [sin,3*cos(y)]
     [1] for (L=[sin,cos,tan];L!=[];L=cdr(L)) {A=car(L);
     print(eval((*A)(@pi/3)));}
     0.86602540349122136831
     0.5000000002
     1.7320508058

References
     *Note `vtype': vtype.

