"SICP Exercise" 147 Exercise 4.3

Exercise 4-3 Original

Exercise 4.3. Rewrite Eval So, the dispatch is the do in data-directed style. Compare this with the datadirected differentiation procedure of exercise 2.73. (You may use the car of a compound expression as the type of the expression, as was appropriate for the syntax implemented In the This section.) .

Analysis

Refer to exercise 2.73.

 (define operation-table make-table)  (define get (operation-table ' Lookup-proc))  (define put (operation-table ' Insert-proc))  (put ' op ' quote text-of-quotation)  (put ' op ' set! eval-assignment)  (put ' op ' define eval-definition)  (put ' op ' if eval-if)  (put ' op ' lambda (Lambda (x y) ( make-procedure (lambda-parameters x) (lambda-body x) y )))  (put ' op ' begin (Lambda (x y) (eval-sequence (  Begin-sequence x  )))  (put ' op ' cond (Lambda (x y) ( evaln (  Cond->if x  )))  (Define (evaln expr env)          (Cond ((self-evaluating expr) expr)                    (variable expr ) (lookup-variable-value expr env))                    (get ' op (car expr)) (Applyn (get ' Op (car expr) expr ( env )))                    (application expr) (Applyn (evaln (operator expr) env ) (list-of-values (operands expr) env )))                    (else(error "unkown expression type--EVAL" expr))                      )) 

"SICP Exercise" 147 Exercise 4.3