Issue: MAP-INTO (version 2)

[Barry Margolin <barmar@Think.COM>]

    Date: Mon, 19 Jun 89 12:16 EDT
    From: David A. Moon <Moon@stony-brook.scrc.symbolics.com>

	The function must take at least as many arguments as there are
	sequences provided, and at least one sequence must be provided.

I suggest relaxing this, to allow zero argument sequences.  The length of
the result-sequence would control the number of times the function is
called.  This would permit something like

	(map-into my-sequence #'(lambda () (random 1.0)))

to fill a sequence with random numbers.

This appears to be what Genera does.

	The arguments result-sequence and each element of sequences can each be
	either a list or a vector (one-dimensional array).  Note that nil is
	considered to be a sequence, of length zero.  If result-sequence and
	each element of sequences are not all the same length, the iteration
	terminates when the shortest sequence is exhausted.

I assume that the result-sequence is included when determining the
shortest sequence.  If result-sequence is a vector with a fill pointer,
or an adjustable vector, how does this affect things?  Intuitively, the
following things seem reasonable:

1) The result-sequence's fill pointer could be set to the number of
elements modified (i.e. the minimum of the sequences' lengths).

2) The result-sequence should be filled as if its fill pointer were
initially 0, and each result is then VECTOR-PUSHed onto the
vector.  This implies (1).

3) When minimizing the sequence lengths, (array-dimension
result-sequence 0) should be used, rather than (length result-sequence),
so that the previous value of the result sequence's fill pointer does
not cause the iteration to terminate prematurely.  This also implies
that the VECTOR-PUSH will never try to go beyond the size of the vector.

In the case where no argument sequences are provided, it might be
reasonable to use (length result-sequence), but I think it would be
better to maintain consistency.  Fill pointers are generally used to
indicate which elements a reader should look at, not to restrict filling
in (for instance, make-array :initial-element initializes ALL the
elements, not just up to the fill pointer).

Genera appears to use (length result-sequence) all the time.

                                                barmar