Exercise 5.48.  The compile-and-go interface implemented in this section 
is awkward, since the compiler can be called only once (when the 
evaluator machine is started). Augment the compiler-interpreter 
interface by providing a compile-and-run primitive that can be called 
from within the explicit-control evaluator as follows:

;;; EC-Eval input:
(compile-and-run
 '(define (factorial n)
    (if (= n 1)
        1
        (* (factorial (- n 1)) n))))
;;; EC-Eval value:
ok
;;; EC-Eval input:
(factorial 5)
;;; EC-Eval value:
120

————————————————————————————————————————————————————————————————————————

$ scheme --load 5.48-load-eceval-compiler.scm

1 ]=> (load "ch5-compiler.scm")
1 ]=> (start-eceval)

;;; EC-Eval input:
(compile-and-run '(define (fac n) (if (= n 1) 1 (* (fac (- n 1)) n))))
;;; EC-Eval value:
ok

;;; EC-Eval input:
(fac 5)
;;; EC-Eval value:
120


--- ch5-eceval-compiler.scm	2001-06-21 12:54:36.000000000 -0600
+++ 5.48-eceval-compiler.scm	2010-06-27 17:56:23.000000000 -0600
@@ -56,6 +56,13 @@
     (set-register-contents! eceval 'val instructions)
     (set-register-contents! eceval 'flag true)
     (start eceval)))
+
+(define (compile-and-keep-going expression)
+  (let ((instructions
+         (assemble (statements
+                    (compile expression 'val 'return))
+                   eceval)))
+    (set-register-contents! eceval 'val instructions)))
 
 ;;**NB. To [not] monitor stack operations, comment in/[out] the line after
 ;; print-result in the machine controller below
@@ -128,6 +135,9 @@
    (list 'compiled-procedure? compiled-procedure?)
    (list 'compiled-procedure-entry compiled-procedure-entry)
    (list 'compiled-procedure-env compiled-procedure-env)
+   (list 'compile-and-run? compile-and-run?)
+   (list 'compile-and-keep-going compile-and-keep-going) ; defined above
+   (list 'compile-and-run-expression compile-and-run-expression)
    ))
 
 (define eceval
@@ -148,8 +158,19 @@
    (op prompt-for-input) (const ";;; EC-Eval input:"))
   (assign exp (op read))
   (assign env (op get-global-environment))
+  (test (op compile-and-run?) (reg exp))
+  (branch (label compile-and-run))
   (assign continue (label print-result))
   (goto (label eval-dispatch))
+compile-and-run
+  (assign exp (op compile-and-run-expression) (reg exp))
+  (assign continue (label compile-and-run-2))
+  (goto (label eval-dispatch))
+compile-and-run-2
+  (perform (op compile-and-keep-going) (reg val))
+  (assign env (op get-global-environment))
+  (assign continue (label print-result))
+  (goto (reg val))
 print-result
 ;;**following instruction optional -- if use it, need monitored stack
   (perform (op print-stack-statistics))


--- ch5-eceval-support.scm	2010-04-22 11:09:43.000000000 -0600
+++ 5.48-eceval-support.scm	2010-06-27 17:42:42.000000000 -0600
@@ -185,3 +185,5 @@
 (define (compiled-procedure-entry c-proc) (cadr c-proc))
 (define (compiled-procedure-env c-proc) (caddr c-proc))
 
+(define (compile-and-run? exp) (tagged-list? exp 'compile-and-run))
+(define (compile-and-run-expression exp) (cadr exp))