DDP Exercise Solution:

(put 'define 'special-forms
     (lambda (var val)
       (put var 'bindings (simp-eval val)) ) )

(put 'if 'special-forms
     (lambda (pred conseq alt)
       (if (simp-eval pred)
           (simp-eval conseq)
           (simp-eval alt) )) )

(put '+ 'bindings +)
(put '* 'bindings *)
(put '= 'bindings =)