lazy.diff

diff --git a/metacircular.scm b/metacircular.scm
index 20542d1..97632e5 100644
--- a/metacircular.scm
+++ b/metacircular.scm
@@ -10,26 +10,43 @@
                                        env))
         ((begin? exp) (eval-sequence (begin-actions exp) env))
         ((cond? exp) (eval (cond->if exp) env))
-        ((application? exp) (apply (eval (operator exp) env)
-                                   (list-of-values (operands exp) env)))
+        ((application? exp) (apply (actual-value (operator exp) env)
+                                   (operands exp)
+                                   env))
         (else
           (error "Unknown expression type -- EVAL" exp))))
 
 (define apply-in-underlying-scheme apply) ;; need it later for primitives
 
-(define (apply procedure arguments)
+(define (apply procedure arguments env)
   (cond ((primitive-procedure? procedure)
-         (apply-primitive-procedure procedure arguments))
+         (apply-primitive-procedure procedure
+                                    (list-of-arg-values arguments env)))
         ((compound-procedure? procedure)
-         (eval-sequence
-           (procedure-body procedure)
-           (extend-environment
-             (procedure-parameters procedure)
-             arguments
-             (procedure-environment procedure))))
+         (eval-sequence (procedure-body procedure)
+                        (extend-environment (procedure-parameters procedure)
+                                            (list-of-delayed-args arguments env)
+                                            (procedure-environment procedure))))
         (else
           (error "Unknown procedure type -- APPLY" procedure))))
 
+;;; thunks
+
+(define (actual-value exp env)
+  (force-it (eval exp env)))
+
+(define (list-of-arg-values exps env)
+  (if (no-operands? exps)
+    '()
+    (cons (actual-value (first-operand exps) env)
+          (list-of-arg-values (rest-operands exps) env))))
+
+(define (list-of-delayed-args exps env)
+  (if (no-operands? exps)
+    '()
+    (cons (delay-it (first-operand exps) env)
+          (list-of-delayed-args (rest-operands exps) env))))
+
 ;;; predicates/selectors 
 
 (define (self-evaluating? exp)
@@ -144,7 +161,7 @@
   'ok)
 
 (define (eval-if exp env)
-  (if (eval (if-predicate exp) env)
+  (if (actual-value (if-predicate exp) env)
     (eval (if-consequent exp) env)
     (eval (if-alternative exp) env)))
 
@@ -257,8 +274,8 @@
 
 ;;; REPL
 
-(define input-prompt ";;; M-Eval input")
-(define output-prompt ";;; M-Eval output")
+(define input-prompt ";;; L-Eval input")
+(define output-prompt ";;; L-Eval output")
 
 (define (prompt-for-input string)
   (newline)
@@ -282,7 +299,7 @@
 (define (driver-loop)
   (prompt-for-input input-prompt)
   (let ((input (read)))
-    (let ((output (eval input the-global-environment)))
+    (let ((output (actual-value input the-global-environment)))
       (announce-output output-prompt)
       (user-print output)))
   (driver-loop))