-;;; KLUDGE: MAP has been rewritten substantially since the fork from
-;;; CMU CL in order to give reasonable performance, but this
-;;; implementation of MAP-INTO still has the same problems as the old
-;;; MAP code. Ideally, MAP-INTO should be rewritten to be efficient in
-;;; the same way that the corresponding cases of MAP have been
-;;; rewritten. Instead of doing it now, though, it's easier to wait
-;;; until we have DYNAMIC-EXTENT, at which time it should become
-;;; extremely easy to define a reasonably efficient MAP-INTO in terms
-;;; of (MAP NIL ..). -- WHN 20000920
+;;;; MAP-INTO
+
+(defmacro map-into-lambda (sequences params &body body)
+ (check-type sequences symbol)
+ `(flet ((f ,params ,@body))
+ (declare (truly-dynamic-extent #'f))
+ ;; Note (MAP-INTO SEQ (LAMBDA () ...)) is a different animal,
+ ;; hence the awkward flip between MAP and LOOP.
+ (if ,sequences
+ (apply #'map nil #'f ,sequences)
+ (loop (f)))))
+
+(define-array-dispatch vector-map-into (data start end fun sequences)
+ (declare (optimize speed (safety 0))
+ (type index start end)
+ (type function fun)
+ (type list sequences))
+ (let ((index start))
+ (declare (type index index))
+ (block mapping
+ (map-into-lambda sequences (&rest args)
+ (declare (truly-dynamic-extent args))
+ (when (eql index end)
+ (return-from mapping))
+ (setf (aref data index) (apply fun args))
+ (incf index)))
+ index))
+
+;;; Uses the machinery of (MAP NIL ...). For non-vectors we avoid
+;;; computing the length of the result sequence since we can detect
+;;; the end during mapping (if MAP even gets that far).
+;;;
+;;; For each result type, define a mapping function which is
+;;; responsible for replacing RESULT-SEQUENCE elements and for
+;;; terminating itself if the end of RESULT-SEQUENCE is reached.
+;;; The mapping function is defined with MAP-INTO-LAMBDA.
+;;;
+;;; MAP-INTO-LAMBDAs are optimized since they are the inner loops.
+;;; Because we are manually doing bounds checking with known types,
+;;; safety is turned off for vectors and lists but kept for generic
+;;; sequences.