change 2htdp/image to export image=?

collects/2htdp/image.rkt

@@ -50,7 +50,8 @@ and they all have good sample contracts. (It is amazing what we can do with kids
          "private/image-more.ss"
          "private/img-err.ss"
          (only-in lang/prim provide-primitive provide-primitives define-primitive)
-         htdp/error)
+         htdp/error
+         (only-in lang/imageeq image=?))
 
 (provide-primitives
          overlay
@@ -137,9 +138,11 @@ and they all have good sample contracts. (It is amazing what we can do with kids
          make-pen pen
          pen?
          step-count?
-         save-image)
+         save-image
+         image=?)
 
-(provide bitmap)
+(provide bitmap 
+         image=?)
 
 (define-primitive make-color build-color/make-color)
 (define-primitive color build-color/color)

collects/2htdp/tests/test-image.rkt

@@ -304,6 +304,25 @@
       =>
       #t)
 
+;; test to make sure that image=? is provided from 2htdp/image and
+;; not just built into the teaching languages.
+(test (image=? (rectangle 10 10 'solid 'red) (rectangle 10 10 'solid 'red))
+      =>
+      #t)
+
+(test (image=? (overlay (rectangle 3 1 'solid 'blue)
+                        (rectangle 1 3 'solid 'blue))
+               (overlay (rectangle 1 3 'solid 'blue)
+                        (rectangle 3 1 'solid 'blue)))
+      =>
+      #t)
+
+
+(test (with-handlers ((exn:fail? (λ (x) 'passed)))
+        (begin (image=? 1 2) 'fail))
+      =>
+      'passed)
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;
 ;;  testing overlays

collects/teachpack/2htdp/scribblings/image.scrbl

@@ -2,7 +2,7 @@
 
 @(require (for-label (only-in racket/contract and/c or/c any/c not/c)
                      2htdp/image
-                     (except-in lang/htdp-beginner posn make-posn posn? posn-x posn-y image?)
+                     (except-in lang/htdp-beginner posn make-posn posn? posn-x posn-y image? image=?)
                      lang/posn
                      racket/gui/base
                      (only-in racket/base path-string?))
@@ -1279,10 +1279,16 @@ Using @racket["pinhole"] or @racket['pinhole] is only allowed when all of the im
 
 @section{Equality Testing of Images}
 
-Two images are equal if they draw exactly the same way at their current size
+Two images are @racket[equal?] if they draw exactly the same way at their current size
 (not neccessarily at all sizes) and, if there are pinholes, the pinholes are
 in the same place.
 
+@defproc[(image=? [i1 image?] [i2 image?]) boolean?]{
+  Tests the same thing as @racket[(equal? i1 i2)], but 
+  insists that its arguments are images, signalling an error
+  otherwise.
+}
+
 @section[#:tag "pinholes"]{Pinholes}
 
 A pinhole is an optional property of an image that identifies a point somewhere