Implement 5.49

ex-5_45-49.scm

@@ -146,7 +146,7 @@
 ; (compile-and-go expression)
 ;; To test this exercise uncomment the previous line, then:
 ;; $ mit-scheme
-;; 1 ]=> (load "ex-5_45-xx")
+;; 1 ]=> (load "ex-5_45-49")
 ;; 2 ]=> (define (g n) (* n n n))
 ;; 3 ]=> (f 3) ; calls interpreted 'g'
 
@@ -155,20 +155,24 @@
 (display "\nex-5.48 - compile-and-run\n")
 
 ;; compile-and-go is implemented in sicp-eceval-compiler.scm
-(start-eceval)
+; (start-eceval)
 ;; To test this exercise uncomment the previous line, then:
 ;; $ mit-scheme
-;; 1 ]=> (load "ex-5_45-xx")
+;; 1 ]=> (load "ex-5_45-49")
 ;; 2 ]=> (compile-and-run (define (f n) (if (= n 1) 1 (* n (f (- n 1))))))
 ;; 3 ]=> (f 5)
 
 (display "[done]\n")
 
-(display "\nex-5.49\n")
+(display "\nex-5.49 - read-compile-execute-print\n")
 
-(display "\nex-5.50\n")
+; Changing the loop to read-compile-execute requies a single additional line
+; within the read-eval-print-loop. If we add a compile-and-run tag to the
+; expression eval-dispatch automatically dispatches to the compiler.
 
+; (assign exp (op list) (const compile-and-run) (reg exp))
+;; read-compile-execute - ex-5.49
+;; Implemented in sicp-eceval-compiler.scm
 
-; (display "\nex-5.51\n")
+(display "[done]\n")
-; (display "\nex-5.52\n")
 

ex-5_50-52.scm

@@ -0,0 +1,24 @@
+(load "shared/util")
+(load "shared/sicp-load-eceval-compiler")
+(load "shared/sicp-compiler")
+
+(display "\nex-5.50 - compile-metacircular-evaluator\n")
+
+; Exercise 5.50.  Use the compiler to compile the metacircular evaluator of
+; section 4.1 and run this program using the register-machine simulator. (To
+; compile more than one definition at a time, you can package the definitions
+; in a begin.) The resulting interpreter will run very slowly because of the
+; multiple levels of interpretation, but getting all the details to work is an
+; instructive exercise.
+
+(compile-and-go
+ '(begin
+    (define (factorial n)
+      (if (= n 1)
+        1
+        (* (factorial (- n 1)) n)))
+    (factorial 10)))
+
+(display "\nex-5.51\n")
+
+(display "\nex-5.52\n")

shared/sicp-eceval-compiler.scm

@@ -61,6 +61,7 @@
 (define (compile-and-run? expression)
   (tagged-list? expression 'compile-and-run))
 (define (compile-and-run expression)
+  (display expression) (newline)
   (let ((instructions
          (assemble (statements
                     (compile (cadr expression) 'val 'return))
@@ -160,9 +161,10 @@ read-eval-print-loop
   (perform (op initialize-stack))
   (perform
    (op prompt-for-input) (const ";;; EC-Eval input:"))
-  (assign exp (op read))
   (assign env (op get-global-environment))
   (assign continue (label print-result))
+  (assign exp (op read))
+  ; (assign exp (op list) (const compile-and-run) (reg exp)) ;; read-compile-execute - ex-5.49
   (goto (label eval-dispatch))
 print-result
 ;;**following instruction optional -- if use it, need monitored stack