Macro stepper:

cleaned up representation of big (localaction) contexts
  unitized hiding impl
  added (broken/experimental) navigation tools (jump, zoom)

svn: r5468

original commit: ef1f77c33fc8082c80b6beea80f6f149ac7f8031

collects/macro-debugger/model/reductions-engine.ss

@@ -44,9 +44,7 @@
     (syntax-rules ()
       [(with-new-local-context e . body)
        (parameterize ([big-context
-                       (cons (cons (current-derivation)
-                                   (cons (list e)
-                                         (context)))
+                       (cons (make-bigframe (current-derivation) (context) (list e) e)
                              (big-context))]
                       [context null])
          . body)]))

collects/macro-debugger/model/steps.ss

@@ -9,8 +9,9 @@
   ;; A Context is a list of Frames
   ;; A Frame is (syntax -> syntax)
 
-  ;; A BigContext is (list-of (cons Derivation (cons Syntaxes Syntax)))
-  ;;   local expansion contexts: deriv, foci, term
+  ;; A BigContext is (list-of BigFrame)
+  ;; A BigFrame is (make-bigframe Derivation Context Syntaxes Syntax)
+  (define-struct bigframe (deriv ctx foci e))
 
   ;; A Reduction is one of 
   ;;   - (make-step ... Syntaxes Syntaxes Syntax Syntax)
@@ -36,6 +37,9 @@
   (define (misstep-term1 s)
     (context-fill (protostep-ctx s) (misstep-e1 s)))
 
+  (define (bigframe-term bf)
+    (context-fill (bigframe-ctx bf) (bigframe-e bf)))
+  
   ;; A StepType is a simple in the following alist.
 
   (define step-type-meanings