expander: bind U+3BB as a macro, not a core form

racket/src/expander/boot/load-handler.rkt

@@ -94,7 +94,7 @@
      [else
       (define (add-top-interaction s)
         (namespace-syntax-introduce
-         (datum->syntax #f (cons '#%top-interaction s))))
+         (datum->syntax s (cons '#%top-interaction s))))
       (call-with-input-file*
        path
        (lambda (i)

racket/src/expander/expand/expr.rkt

@@ -60,7 +60,8 @@
               sc-formals)
           exp-body))
 
-(define (make-expand-lambda get-lambda)
+(add-core-form!
+ 'lambda
   (lambda (s ctx)
     (log-expand ctx 'prim-lambda)
     (define disarmed-s (syntax-disarm s))
@@ -72,20 +73,28 @@
         (parsed-lambda rebuild-s formals body)
         (rebuild
          rebuild-s
-         `(,(get-lambda ctx (m 'lambda)) ,formals ,@body)))))
-
-(add-core-form!
- 'lambda
- (make-expand-lambda (lambda (ctx lam-id) lam-id)))
+         `(,(m 'lambda) ,formals ,@body)))))
 
 (add-core-form!
  'λ
- (make-expand-lambda
-  (lambda (ctx lam-id)
-    (datum->syntax (syntax-shift-phase-level core-stx (expand-context-phase ctx))
-                   'lambda
-                   lam-id
-                   lam-id))))
+ ;; A macro:
+ (lambda (s)
+   (define-match m s '(lam-id formals _ ...+))
+   (define ids (parse-and-flatten-formals (m 'formals) #f s))
+   (define ctx (get-current-expand-context #:fail-ok? #t))
+   (define phase (if ctx
+                     (expand-context-phase ctx)
+                     0))
+   (check-no-duplicate-ids ids phase s #:what "argument name")
+   (datum->syntax
+    s
+    (cons (datum->syntax (syntax-shift-phase-level core-stx phase)
+                         'lambda
+                         (m 'lam-id)
+                         (m 'lam-id))
+          (cdr (syntax-e s)))
+    s
+    s)))
 
 (add-core-form!
  'case-lambda
@@ -125,7 +134,9 @@
      [(pair? formals)
       (unless (identifier? (car formals))
         (raise-syntax-error #f "not an identifier" s (car formals)))
-      (cons (add-scope (car formals) sc)
+      (cons (if sc
+                (add-scope (car formals) sc)
+                (car formals))
             (loop (cdr formals)))]
      [(null? formals)
       null]

racket/src/expander/namespace/core.rkt

@@ -111,7 +111,11 @@
                      (for ([(sym val) (in-hash core-primitives)])
                        (namespace-set-consistent! ns 0 sym val))
                      (for ([(sym proc) (in-hash core-forms)])
-                       (namespace-set-transformer! ns 0 sym (core-form proc sym)))])))
+                       (namespace-set-transformer! ns 0 sym (if (procedure-arity-includes? proc 2)
+                                                                ;; An actual core form:
+                                                                (core-form proc sym)
+                                                                ;; A macro:
+                                                                proc)))])))
    core-module-name))
 
 ;; Helper for recognizing and dispatching on core forms: