disable nested `#lang'

A `syntax/module-reader' reader disables `#lang' when looping to
read a module body. The HtDP languages require a little additional
treatment.

collects/lang/htdp-reader.rkt

@@ -10,11 +10,12 @@
       read))
   
   (define (get-all-exps source-name port)
-    (let loop ()
+    (parameterize ([read-accept-lang #f])
-      (let ([exp (read-syntax source-name port)])
+      (let loop ()
-        (cond
+        (let ([exp (read-syntax source-name port)])
-          [(eof-object? exp) null]
+          (cond
-          [else (cons exp (loop))]))))
+           [(eof-object? exp) null]
+           [else (cons exp (loop))])))))
   
   (define (lookup key table)
     (let ([ans (assoc key table)])

collects/lang/run-teaching-program.rkt

@@ -90,7 +90,8 @@
 
 ;; take all of the body expressions from the port
 (define (suck-all-exps port reader)
-  (define (port-reader p) (reader (object-name port) p))
+  (define (port-reader p) (parameterize ([read-accept-lang #f])
+                            (reader (object-name port) p)))
   (sequence->list (in-port port-reader port)))
 
 ;; check that the teachpacks exist, return 

collects/syntax/module-reader.rkt

@@ -175,12 +175,13 @@
     (let* ([lang (if stx? (datum->syntax #f lang modpath modpath) lang)]
            [body (lambda ()
                    (if whole?
-                     (read port)
+                       (read port)
-                     (let loop ([a null])
+                       (parameterize ([read-accept-lang #f])
-                       (let ([v (read port)])
+                         (let loop ([a null])
-                         (if (eof-object? v)
+                           (let ([v (read port)])
-                             (reverse a)
+                             (if (eof-object? v)
-                             (loop (cons v a)))))))]
+                                 (reverse a)
+                                 (loop (cons v a))))))))]
            [body (cond [(not wrapper)   (body)]
                        [(ar? wrapper 2) (wrapper body stx?)]
                        [else            (wrapper body)])]

collects/syntax/scribblings/module-reader.scrbl

@@ -94,7 +94,12 @@ identifiers used by the @racket[reader-option]s.
        @racket[read-syntax], respectively. Normally, the replacements
        for @racket[read] and @racket[read-syntax] are applied
        repeatedly to the module source until @racket[eof] is produced,
-       but see also @racket[#:whole-body-readers?].
+       but see also @racket[#:whole-body-readers?]. 
+
+       Unless @racket[#:whole-body-readers?] specifies a true value,
+       the repeated use of @racket[read] or @racket[read-syntax] is
+       @racket[parameterize]d to set @racket[read-accept-lang] to
+       @racket[#f], which disables nested uses of @hash-lang[].
 
         See also @racket[#:wrapper1] and @racket[#:wrapper2], which
         support simple parameterization of readers rather than

doc/release-notes/racket/HISTORY.txt

@@ -1,6 +1,9 @@
 Version 5.3.0.10
 racket/base: add progress-evt?, thread-cell-values?, prefab-key?,
  semaphore-peek-evt?, channel-put-evt?
+Changed #lang for most languages so that it cannot be nested;
+ this change is within syntax/module-reader and applies to
+ racket, racket/base, and more
 
 Version 5.3.0.9
 Changed the format of error messages

src/racket/src/read.c

@@ -2184,14 +2184,19 @@ _internal_read(Scheme_Object *port, Scheme_Object *stxsrc, int crc, int cant_fai
     else
       params.table = NULL;
   }
-  params.can_read_compiled = crc;
+  if (crc >= 0)
+    params.can_read_compiled = crc;
+  else {
+    v = scheme_get_param(scheme_current_config(), MZCONFIG_CAN_READ_COMPILED);
+    params.can_read_compiled = SCHEME_TRUEP(v);
+  }
   v = scheme_get_param(config, MZCONFIG_CAN_READ_PIPE_QUOTE);
   params.can_read_pipe_quote = SCHEME_TRUEP(v);
   v = scheme_get_param(config, MZCONFIG_CAN_READ_BOX);
   params.can_read_box = SCHEME_TRUEP(v);
   v = scheme_get_param(config, MZCONFIG_CAN_READ_GRAPH);
   params.can_read_graph = SCHEME_TRUEP(v);
-  if (crc || get_info) {
+  if ((crc > 0) || get_info) {
     params.can_read_reader = 1;
     params.can_read_lang = 1;
   } else {
@@ -2329,9 +2334,6 @@ scheme_internal_read(Scheme_Object *port, Scheme_Object *stxsrc, int crc, int ca
 {
   Scheme_Thread *p = scheme_current_thread;
 
-  if (crc < 0)
-    crc = SCHEME_TRUEP(scheme_get_param(scheme_current_config(), MZCONFIG_CAN_READ_COMPILED));
-
   if (cantfail) {
     return _internal_read(port, stxsrc, crc, cantfail, recur, expose_comment, -1, NULL, 
                           magic_sym, magic_val, delay_load_info, 0);