[New function: get-instances-limit
clinton@unknownlamer.org**20080106183329
 Identical to elephant:get-instances-by-range, but only returns at most
 LIMIT instances. The implementation is a bit lame now: it uses a
 closure that tracks the limit and accumulates the results in a private
 list. This wastes LIMIT cons since map-index is already allocating the
 list. A better solution would be to add a :limit argument to the
 Elephant query functions.
] {
hunk ./src/database.lisp 2
+
+;;; Basic Query Functions
+
+(define-condition results-limit-reached (error)
+  ((count :initarg :count :reader limit-count)
+   (result :initarg :result :reader limit-result)))
+
+(defun make-index-mapper (fn limit)
+  (let ((curr 0)
+	(results '()))
+    (lambda (&rest args)
+      (cond ((= curr limit)
+	     (error 'results-limit-reached
+		    :count curr :result (nreverse results)))
+	    (t (incf curr)
+	       (car (push (apply fn args) results)))))))
+
+(defgeneric get-instances-limit (class slot-name start end &optional limit))
+
+(defmethod get-instances-limit ((class symbol) slot-name start end &optional limit)
+  (get-instances-limit (find-class class) slot-name start end limit))
+
+(defmethod get-instances-limit ((class persistent-metaclass) slot-name start end
+				&optional limit)
+  (if limit
+      (handler-case
+	  (map-inverted-index (make-index-mapper #'elephant::identity2 limit)
+			      class slot-name :start start :end end :collect t)
+	(results-limit-reached (c) (values (limit-result c) (limit-count c))))
+      (get-instances-by-range class slot-name start end)))
hunk ./src/packages.lisp 26
+   :get-instances-limit
}