Things to consider for CLtL'97

[David C. Plummer <DCP@SCRC-QUABBIN.ARPA>]

    Date: Fri, 28 Feb 86 15:04 EST
    From: Guy Steele <gls@THINK-AQUINAS.ARPA>

	Date: Tue, 25 Feb 86 11:15 EST
	From: David C. Plummer <DCP@SCRC-QUABBIN.ARPA>

	reduce should have a :KEY keyword argument.  For example, suppose you
	have a sequence of sequences, and you want to know the sum of the
	lengths of the inner sequences.  Currently, I think you have to do
		(reduce #'(lambda (so-far subsequence)
			    (+ so-far (length sub-sequence)))
			sequence)
	but I would prefer to do
		(reduce #'+ sequence :key #'length)

    (REDUCE #'+ (MAP (TYPE-OF sequence) #'length sequence))

Yours conses.  Mine doesn't.

	There should be a modify-seq (or some name) that looks roughly like
		modify-seq sequence modifier &key start end from-end test test-not
	that modifies the elements of the sequence between start and end that
	past the TEST function.  The element is replaced by the modifier applied
	to the old element.  For example, if a sequence is a sequence of
	integers and you want to change it into a sequence of arrays whose
	lengths are based on those integers, one could do
		(modify-seq sequence #'(lambda (n) (make-array (round (* n 1.1)))))

	There should be a modify-hash function.

    This isn't consistent with the syntax of other functions that have a test.
    Did you mean:

[I assume this is in response to modify-seq instead of modify-hash.]

	modify-seq item sequence modifier &key start end from-end test test-not
	modify-seq-if predicate sequence modifier &key start end from-end
	modify-seq-if-not predicate item sequence modifier &key start end from-end

    ?  
I see, I think.  Yes, I want the -IF and -IF-NOT forms as well.
    And should they all also take a :KEY argument?
I don't think so.  Consider what :KEY does.  It extracts a part of the
datastructure.  To put it back, the implementation would have to do
something like
	(setf (funcall key sequence-element)
	      (funcall modifier
		       (funcall key sequence-element)))
and SETF of FUNCALL isn't generally invertable.