From 89b96ef9f30391bfe53738c74b8258fa0c3dc928 Mon Sep 17 00:00:00 2001
From: John Clements <clements@racket-lang.org>
Date: Sun, 18 May 2014 00:18:54 -0700
Subject: [PATCH] simplify stepper and fix unevaluated id bug

---
 pkgs/htdp-pkgs/htdp-lib/stepper/DESIGN-NOTES      | 14 ++++++++++++++
 .../htdp-lib/stepper/private/annotate.rkt         | 15 ++++-----------
 pkgs/htdp-pkgs/htdp-lib/stepper/private/model.rkt |  1 +
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/pkgs/htdp-pkgs/htdp-lib/stepper/DESIGN-NOTES b/pkgs/htdp-pkgs/htdp-lib/stepper/DESIGN-NOTES
index db1547d503..79d351879f 100644
--- a/pkgs/htdp-pkgs/htdp-lib/stepper/DESIGN-NOTES
+++ b/pkgs/htdp-pkgs/htdp-lib/stepper/DESIGN-NOTES
@@ -962,3 +962,17 @@ code, and works better, too.
 Nice to be here again...
 
 2010-12-04
+
+**************
+
+How time flies. Small bug fixes; it's now illegal to refer to undefined
+values. That is, (letrec ([a a]) 3) is illegal.  This caused stepper
+breakage, and I was worried that fixing this was going to require some
+terrible deep surgery.  In fact, though, it looks like this change
+makes things *simpler*; it looks like I was going out of my way to
+preserve the undefined values for situations where it might turn up in
+student programs, and now I can omit that check.
+
+2013-05-18
+
+**************
diff --git a/pkgs/htdp-pkgs/htdp-lib/stepper/private/annotate.rkt b/pkgs/htdp-pkgs/htdp-lib/stepper/private/annotate.rkt
index aabeab2901..0150c8d83b 100644
--- a/pkgs/htdp-pkgs/htdp-lib/stepper/private/annotate.rkt
+++ b/pkgs/htdp-pkgs/htdp-lib/stepper/private/annotate.rkt
@@ -436,7 +436,7 @@
       ;  wish me luck.
       
       
-      (define (let-abstraction stx output-identifier make-init-list)
+      (define (let-abstraction stx output-identifier)
         (with-syntax ([(_ ([(var ...) val] ...) . bodies) stx])
           (match-let*
               ([binding-sets (map syntax->list (syntax->list #'((var ...) ...)))]
@@ -491,7 +491,7 @@
                                                     free-varref-sets-vals)) 
                             binding-list)]
              [counter-id #`lifting-counter]
-             [unevaluated-list (make-init-list binding-list)]
+             [unevaluated-list (map (lambda (b) *unevaluated*)  binding-list)]
              [outer-initialization
               #`([(#,@lifted-vars #,@binding-list #,let-counter)
                   (values #,@(append (map (lambda (dc_binding) counter-id)
@@ -788,16 +788,9 @@
                                          #,rolled-into-fakes))
                            all-free-vars))]
                                             
-                [(let-values . _)
-                 (let-abstraction exp 
-                                  #`let-values
-                                  (lambda (bindings)
-                                    (map (lambda (_) *unevaluated*) bindings)))]
+                [(let-values . _) (let-abstraction exp #`let-values)]
                 
-                [(letrec-values . _)
-                 (let-abstraction exp 
-                                  #`letrec-values
-                                  (lambda (bindings) (map (lambda (b) #`#,b) bindings)))]
+                [(letrec-values . _) (let-abstraction exp #`letrec-values)]
                 
                 
                 ;                          $   
diff --git a/pkgs/htdp-pkgs/htdp-lib/stepper/private/model.rkt b/pkgs/htdp-pkgs/htdp-lib/stepper/private/model.rkt
index 8dea5d1d7e..785d02b26e 100644
--- a/pkgs/htdp-pkgs/htdp-lib/stepper/private/model.rkt
+++ b/pkgs/htdp-pkgs/htdp-lib/stepper/private/model.rkt
@@ -522,6 +522,7 @@
   ;; step through a single expanded expression.
   (define (step-through-expression expanded)  
     (define annotated (a:annotate expanded break show-lambdas-as-lambdas?))
+    #;(printf "annotated: ~s\n" annotated)
     (parameterize ([test-engine:test-silence #t])
       (eval-syntax annotated)))