fix HtDP local' to work better with macros that expand to begin'

In particular, the forms within `begin' need to be partially
expanded before checking whether they're allowed.

collects/lang/private/teach.rkt

@@ -1636,13 +1636,13 @@
 		  ;;  forms know that it's ok to expand in this internal
 		  ;;  definition context.
 		  [int-def-ctx (build-expand-context (make-expanding-for-intermediate-local))])
-	      (let* ([partly-expanded-defns 
+	      (let* ([partly-expand (lambda (d)
-		      (map (lambda (d)
                                       (local-expand
                                        d
                                        int-def-ctx
-			      (kernel-form-identifier-list)))
+                                       (kernel-form-identifier-list)))]
-			   defns)]
+                     [partly-expanded-defns
+		      (map partly-expand defns)]
 		     [flattened-defns
 		      (let loop ([l partly-expanded-defns][origs defns])
 			(apply
@@ -1653,7 +1653,7 @@
 				  ;; or `define-syntaxes', because only macros can generate
 				  ;; them
 				  [(begin defn ...)
-				   (let ([l (syntax->list (syntax (defn ...)))])
+				   (let ([l (map partly-expand (syntax->list (syntax (defn ...))))])
 				     (loop l l))]
 				  [(define-values . _)
 				   (list d)]

collects/tests/htdp-lang/intm-adv.rktl

@@ -115,3 +115,15 @@
 (htdp-err/rt-test (-) (exn-type-and-msg exn:application:arity? "-: expects at least 1 argument, given 0"))
 (htdp-err/rt-test (/) (exn-type-and-msg exn:application:arity? "/: expects at least 1 argument, given 0"))
 ;(htdp-test 1 (/ 1) exn:application:arity?)
+
+;; Check that `local' works with macros that expand to `begin':
+(module my-multi-defn racket/base
+  (provide multi)
+  (define-syntax-rule (multi a b)
+    (begin
+      (define a 1)
+      (define b 2))))
+(htdp-teachpack my-multi-defn)
+
+(htdp-test '(2 1) 'local (local [(multi x y)]
+                           (list y x)))