adding unambiguous promise? to core

lib/init-7.scm

@@ -1079,8 +1079,11 @@
  (auto-force
   )
  (else
+  (define *promise-tag* (list 'promise))
   (define (promise done? proc)
-    (list (cons done? proc)))
+    (cons (cons done? proc) *promise-tag*))
+  (define (promise? x)
+    (and (pair? x) (eq? *promise-tag* (cdr x))))
   (define (promise-done? x) (car (car x)))
   (define (promise-value x) (cdr (car x)))
   (define (promise-update! new old)

lib/scheme/lazy.sld

@@ -4,16 +4,4 @@
   (export delay force delay-force make-promise promise?)
   (begin
     (define (make-promise x)
-      (delay x)))
-  (cond-expand
-   (auto-force
-    )
-   (else
-    (begin
-      (define (promise? x)
-        (and (pair? x)
-             (null? (cdr x))
-             (pair? (car x))
-             (or (eq? #t (caar x))
-                 (and (eq? #f (caar x))
-                      (procedure? (cdar x))))))))))
+      (delay x))))