6.001 Structure and Interpretation of Computer Programs. Copyright o 2004 by Massachusetts Institute of Technology Slide 17.1.15 Then, do the same thing for the second interior begin N。 rmal Order Example expression, since is a primitive procedure and requires its write-line inside too") arguments be evaluated +xx)) (foo (begin (write-line eval arg")222) +(begin (w-l eval arg")222 egin (w-l eval arg") 222)) ev滴1画E Normal order Example Slide 17.1.16 dene(f。x hen actually apply the primitive procedure to the arguments, (write-line inside foo") and return the value foo (begin (write-line eval arg") 222)) a>(begin (writo-line de too") egin (w-l eval arg") ⊥ns⊥ de toc Slide 1.1.17 Normal Order Example So now we see there is a difference in behavior remember in the applicative order case, we noted that we first evaluated the te-line " inside foo"> argument(once)and then we went inside the procedure Here, it's as if we substituted the unevaluated arguments into f。。( begin( write-1ine"eva1arg")222)) the body of the procedure. Thus we first went inside the a> (begin (write-line "inside foo") procedure, then when required by a primitive procedure, we w-l eval arg") 22 evaluate the argument. And since it has been substituted twice into the body, we evaluate it twice body of the procedure Our goal then is to note that normal order has a different behavior: substitute until required to evaluate. Applicative was get value, then substitute. So why is this a useful change to make? And how do we change our evaluator to achieve normal der evolution 6.001 Notes: Section 17.26.001 Structure and Interpretation of Computer Programs. Copyright © 2004 by Massachusetts Institute of Technology. Slide 17.1.15 Then, do the same thing for the second interior begin expression, since + is a primitive procedure and requires its arguments be evaluated. Slide 17.1.16 Then actually apply the primitive procedure to the arguments, and return the value. Slide 17.1.17 So now we see there is a difference in behavior. Remember in the applicative order case, we noted that we first evaluated the argument (once) and then we went inside the procedure. Here, it’s as if we substituted the unevaluated arguments into the body of the procedure. Thus we first went inside the procedure, then when required by a primitive procedure, we evaluate the argument. And since it has been substituted twice into the body, we evaluate it twice. Our goal then is to note that normal order has a different behavior: substitute until required to evaluate. Applicative was: get value, then substitute. So why is this a useful change to make? And how do we change our evaluator to achieve normal order evolution. 6.001 Notes: Section 17.2